* [PATCH v4 1/7] dmaengine: dw: Fix XFER bit set, but channel not idle error
2026-10-29 22:29 [PATCH v4 0/7] dmaengine: dw: serialize completion and termination James Hilliard
@ 2026-10-29 22:29 ` James Hilliard
2026-10-29 22:29 ` [PATCH v4 2/7] dmaengine: dw: serialize error recovery with channel termination James Hilliard
` (5 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: James Hilliard @ 2026-10-29 22:29 UTC (permalink / raw)
To: Viresh Kumar, Andy Shevchenko, Vinod Koul, Frank Li, Dan Williams
Cc: Serge Semin, Greg Kroah-Hartman, Jiri Slaby, Ilpo Järvinen,
dmaengine, linux-serial, linux-kernel, Sashiko,
Lars-Peter Clausen, James Hilliard, stable, Frank Li
From: Serge Semin <fancer.lancer@gmail.com>
If a client driver gets to use the DW DMAC engine device tougher
than usual, with occasional DMA-transfers termination and restart, then
the next error can be randomly spotted in the system log:
> dma dma0chan0: BUG: XFER bit set, but channel not idle!
For instance that happens in case of the 8250 UART port driver handling
the looped back high-speed traffic (in my case > 1.5Mbaud) by means of the
DMA-engine interface.
The error happens due to the two-staged nature of the DW DMAC IRQs
handling procedure and due to the critical section break in the meantime.
In particular in case if the DMA-transfer is terminated and restarted:
1. after the IRQ-handler submitted the tasklet but before the tasklet
started handling the DMA-descriptors in dwc_scan_descriptors();
2. after the XFER completion flag was detected in the
dwc_scan_descriptors() method, but before the dwc_complete_all() method
is called
the error denoted above is printed due to the overlap of the last transfer
completion and the new transfer execution stages.
Clear the channel interrupt status when stopping it, and keep the XFER
check, descriptor detachment and queued-transfer restart in one locked
section. An empty active list needs no completion processing.
When the locked XFER recheck finds no event, only update residue. A stale
tasklet snapshot may belong to a terminated transfer, and a zero residue
only means the source has been read, not that destination writes have
finished. Requiring RAW.XFER also prevents the fallback scan from freeing
a descriptor still linked on active_list.
Fixes: 69cea5a00d31 ("dmaengine/dw_dmac: Replace spin_lock* with irqsave variants and enable submission from callback")
Fixes: 3bfb1d20b547 ("dmaengine: Driver for the Synopsys DesignWare DMA controller")
Cc: stable@vger.kernel.org
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
[james: require a locked XFER event and handle an empty active list]
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
---
drivers/dma/dw/core.c | 70 ++++++++++++++++++++-------------------------------
1 file changed, 27 insertions(+), 43 deletions(-)
diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index dd75f97a33b3..07a5f5105787 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -141,6 +141,12 @@ static inline void dwc_chan_disable(struct dw_dma *dw, struct dw_dma_chan *dwc)
channel_clear_bit(dw, CH_EN, dwc->mask);
while (dma_readl(dw, CH_EN) & dwc->mask)
cpu_relax();
+
+ dma_writel(dw, CLEAR.XFER, dwc->mask);
+ dma_writel(dw, CLEAR.BLOCK, dwc->mask);
+ dma_writel(dw, CLEAR.SRC_TRAN, dwc->mask);
+ dma_writel(dw, CLEAR.DST_TRAN, dwc->mask);
+ dma_writel(dw, CLEAR.ERROR, dwc->mask);
}
/*----------------------------------------------------------------------*/
@@ -257,34 +263,6 @@ dwc_descriptor_complete(struct dw_dma_chan *dwc, struct dw_desc *desc,
dmaengine_desc_callback_invoke(&cb, NULL);
}
-static void dwc_complete_all(struct dw_dma *dw, struct dw_dma_chan *dwc)
-{
- struct dw_desc *desc, *_desc;
- LIST_HEAD(list);
- unsigned long flags;
-
- spin_lock_irqsave(&dwc->lock, flags);
- if (dma_readl(dw, CH_EN) & dwc->mask) {
- dev_err(chan2dev(&dwc->chan),
- "BUG: XFER bit set, but channel not idle!\n");
-
- /* Try to continue after resetting the channel... */
- dwc_chan_disable(dw, dwc);
- }
-
- /*
- * Submit queued descriptors ASAP, i.e. before we go through
- * the completed ones.
- */
- list_splice_init(&dwc->active_list, &list);
- dwc_dostart_first_queued(dwc);
-
- spin_unlock_irqrestore(&dwc->lock, flags);
-
- list_for_each_entry_safe(desc, _desc, &list, desc_node)
- dwc_descriptor_complete(dwc, desc, true);
-}
-
/* Returns how many bytes were already received from source */
static inline u32 dwc_get_sent(struct dw_dma_chan *dwc)
{
@@ -302,6 +280,7 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
struct dw_desc *child;
u32 status_xfer;
unsigned long flags;
+ LIST_HEAD(list);
spin_lock_irqsave(&dwc->lock, flags);
llp = channel_readl(dwc, LLP);
@@ -310,6 +289,10 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
if (status_xfer & dwc->mask) {
/* Everything we've submitted is done */
dma_writel(dw, CLEAR.XFER, dwc->mask);
+ if (list_empty(&dwc->active_list)) {
+ spin_unlock_irqrestore(&dwc->lock, flags);
+ return;
+ }
if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
struct list_head *head, *active = dwc->tx_node_active;
@@ -341,9 +324,23 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
clear_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags);
}
+ if (dma_readl(dw, CH_EN) & dwc->mask) {
+ dev_err(chan2dev(&dwc->chan),
+ "BUG: XFER bit set, but channel not idle!\n");
+
+ /* Try to continue after resetting the channel... */
+ dwc_chan_disable(dw, dwc);
+ }
+
+ /* Detach the completed transfer before starting queued work. */
+ list_splice_init(&dwc->active_list, &list);
+ dwc_dostart_first_queued(dwc);
spin_unlock_irqrestore(&dwc->lock, flags);
- dwc_complete_all(dw, dwc);
+ list_for_each_entry_safe(desc, _desc, &list, desc_node) {
+ list_del_init(&desc->desc_node);
+ dwc_descriptor_complete(dwc, desc, true);
+ }
return;
}
@@ -389,22 +386,9 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
desc->residue -= child->len;
}
- /*
- * No descriptors so far seem to be in progress, i.e.
- * this one must be done.
- */
- spin_unlock_irqrestore(&dwc->lock, flags);
- dwc_descriptor_complete(dwc, desc, true);
- spin_lock_irqsave(&dwc->lock, flags);
}
- dev_err(chan2dev(&dwc->chan),
- "BUG: All descriptors done, but channel not idle!\n");
-
- /* Try to continue after resetting the channel... */
- dwc_chan_disable(dw, dwc);
-
- dwc_dostart_first_queued(dwc);
+ /* Residue describes source reads; only RAW.XFER completes a transfer. */
spin_unlock_irqrestore(&dwc->lock, flags);
}
--
2.53.0
^ permalink raw reply [flat|nested] 8+ messages in thread* [PATCH v4 2/7] dmaengine: dw: serialize error recovery with channel termination
2026-10-29 22:29 [PATCH v4 0/7] dmaengine: dw: serialize completion and termination James Hilliard
2026-10-29 22:29 ` [PATCH v4 1/7] dmaengine: dw: Fix XFER bit set, but channel not idle error James Hilliard
@ 2026-10-29 22:29 ` James Hilliard
2026-10-29 22:29 ` [PATCH v4 3/7] dmaengine: dw: complete cookies before releasing the channel lock James Hilliard
` (4 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: James Hilliard @ 2026-10-29 22:29 UTC (permalink / raw)
To: Viresh Kumar, Andy Shevchenko, Vinod Koul, Frank Li, Dan Williams
Cc: Serge Semin, Greg Kroah-Hartman, Jiri Slaby, Ilpo Järvinen,
dmaengine, linux-serial, linux-kernel, Sashiko,
Lars-Peter Clausen, James Hilliard, stable, Frank Li
The tasklet samples RAW.ERROR before taking the channel lock. A
concurrent termination can empty the active list before dwc_handle_error()
uses that cached error to select a descriptor. The list head is then
interpreted as a descriptor. Even with an active descriptor, moving
queue.next unconditionally can put an empty queue's head on the active
list and pass it to dwc_dostart().
Recheck the error status under the channel lock and stop the channel
before selecting its failed descriptor. Only one transaction is issued
at a time, so take that descriptor directly instead of scanning for
completions first. The scan can otherwise complete it and start queued
work before the error handler has identified the failed transaction.
Detach the failed descriptor under the same lock and use the queued-start
helper, which leaves an empty queue alone. Clear the software-LLP flag
before restarting so a failed multiblock transfer does not prevent the
next transaction from starting. Keep the completion callback outside the
lock, with the detached descriptor owned by the tasklet.
Fixes: 3bfb1d20b547 ("dmaengine: Driver for the Synopsys DesignWare DMA controller")
Fixes: f336e42f73d9 ("dw_dmac: Move single descriptor from dwc->queue to dwc->active_list in dwc_complete_all")
Cc: stable@vger.kernel.org
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
---
drivers/dma/dw/core.c | 22 ++++++++++++++--------
1 file changed, 14 insertions(+), 8 deletions(-)
diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 07a5f5105787..51c5460b4670 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -408,10 +408,17 @@ static void dwc_handle_error(struct dw_dma *dw, struct dw_dma_chan *dwc)
struct dw_desc *child;
unsigned long flags;
- dwc_scan_descriptors(dw, dwc);
-
spin_lock_irqsave(&dwc->lock, flags);
+ /* Termination may have cleared the error since the tasklet sampled it. */
+ if (!(dma_readl(dw, RAW.ERROR) & dwc->mask))
+ goto unlock;
+
+ dwc_chan_disable(dw, dwc);
+ clear_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags);
+ if (list_empty(&dwc->active_list))
+ goto unlock;
+
/*
* The descriptor currently at the head of the active list is
* borked. Since we don't have any way to report errors, we'll
@@ -419,12 +426,7 @@ static void dwc_handle_error(struct dw_dma *dw, struct dw_dma_chan *dwc)
*/
bad_desc = dwc_first_active(dwc);
list_del_init(&bad_desc->desc_node);
- list_move(dwc->queue.next, dwc->active_list.prev);
-
- /* Clear the error flag and try to restart the controller */
- dma_writel(dw, CLEAR.ERROR, dwc->mask);
- if (!list_empty(&dwc->active_list))
- dwc_dostart(dwc, dwc_first_active(dwc));
+ dwc_dostart_first_queued(dwc);
/*
* WARN may seem harsh, but since this only happens
@@ -443,6 +445,10 @@ static void dwc_handle_error(struct dw_dma *dw, struct dw_dma_chan *dwc)
/* Pretend the descriptor completed successfully */
dwc_descriptor_complete(dwc, bad_desc, true);
+ return;
+
+unlock:
+ spin_unlock_irqrestore(&dwc->lock, flags);
}
static void dw_dma_tasklet(struct tasklet_struct *t)
--
2.53.0
^ permalink raw reply [flat|nested] 8+ messages in thread* [PATCH v4 3/7] dmaengine: dw: complete cookies before releasing the channel lock
2026-10-29 22:29 [PATCH v4 0/7] dmaengine: dw: serialize completion and termination James Hilliard
2026-10-29 22:29 ` [PATCH v4 1/7] dmaengine: dw: Fix XFER bit set, but channel not idle error James Hilliard
2026-10-29 22:29 ` [PATCH v4 2/7] dmaengine: dw: serialize error recovery with channel termination James Hilliard
@ 2026-10-29 22:29 ` James Hilliard
2026-10-29 22:29 ` [PATCH v4 4/7] dmaengine: dw: calculate residue separately from completion James Hilliard
` (3 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: James Hilliard @ 2026-10-29 22:29 UTC (permalink / raw)
To: Viresh Kumar, Andy Shevchenko, Vinod Koul, Frank Li, Dan Williams
Cc: Serge Semin, Greg Kroah-Hartman, Jiri Slaby, Ilpo Järvinen,
dmaengine, linux-serial, linux-kernel, Sashiko,
Lars-Peter Clausen, James Hilliard, stable
Completion detaches a descriptor from the active list under the channel
lock, but updates its cookie later when freeing it. Termination can take
the lock in between and complete newer descriptors. Completing the older
cookie afterwards moves completed_cookie backwards and makes an already
terminated transfer appear outstanding again.
Complete cookies while detaching descriptors in the completion, error
recovery and termination paths. Keep the active-before-queued ordering
when terminating so completed_cookie advances in submission order.
Descriptor freeing and client notification no longer update cookies.
Fixes: 3bfb1d20b547 ("dmaengine: Driver for the Synopsys DesignWare DMA controller")
Cc: stable@vger.kernel.org
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
drivers/dma/dw/core.c | 24 +++++++++++++++---------
1 file changed, 15 insertions(+), 9 deletions(-)
diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 51c5460b4670..1f7afcd01565 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -236,18 +236,17 @@ static void dwc_dostart_first_queued(struct dw_dma_chan *dwc)
/*----------------------------------------------------------------------*/
static void
-dwc_descriptor_complete(struct dw_dma_chan *dwc, struct dw_desc *desc,
- bool callback_required)
+dwc_descriptor_free(struct dw_dma_chan *dwc, struct dw_desc *desc,
+ bool callback_required)
{
struct dma_async_tx_descriptor *txd = &desc->txd;
struct dw_desc *child;
unsigned long flags;
struct dmaengine_desc_callback cb;
- dev_vdbg(chan2dev(&dwc->chan), "descriptor %u complete\n", txd->cookie);
+ dev_vdbg(chan2dev(&dwc->chan), "freeing descriptor %p\n", desc);
spin_lock_irqsave(&dwc->lock, flags);
- dma_cookie_complete(txd);
if (callback_required)
dmaengine_desc_get_callback(txd, &cb);
else
@@ -334,12 +333,14 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
/* Detach the completed transfer before starting queued work. */
list_splice_init(&dwc->active_list, &list);
+ list_for_each_entry(desc, &list, desc_node)
+ dma_cookie_complete(&desc->txd);
dwc_dostart_first_queued(dwc);
spin_unlock_irqrestore(&dwc->lock, flags);
list_for_each_entry_safe(desc, _desc, &list, desc_node) {
list_del_init(&desc->desc_node);
- dwc_descriptor_complete(dwc, desc, true);
+ dwc_descriptor_free(dwc, desc, true);
}
return;
}
@@ -441,10 +442,11 @@ static void dwc_handle_error(struct dw_dma *dw, struct dw_dma_chan *dwc)
list_for_each_entry(child, &bad_desc->tx_list, desc_node)
dwc_dump_lli(dwc, child);
+ /* Pretend the descriptor completed successfully */
+ dma_cookie_complete(&bad_desc->txd);
spin_unlock_irqrestore(&dwc->lock, flags);
- /* Pretend the descriptor completed successfully */
- dwc_descriptor_complete(dwc, bad_desc, true);
+ dwc_descriptor_free(dwc, bad_desc, true);
return;
unlock:
@@ -945,12 +947,16 @@ static int dwc_terminate_all(struct dma_chan *chan)
/* active_list entries will end up before queued entries */
list_splice_init(&dwc->queue, &list);
list_splice_init(&dwc->active_list, &list);
+ list_for_each_entry(desc, &list, desc_node)
+ dma_cookie_complete(&desc->txd);
spin_unlock_irqrestore(&dwc->lock, flags);
/* Flush all pending and queued descriptors */
- list_for_each_entry_safe(desc, _desc, &list, desc_node)
- dwc_descriptor_complete(dwc, desc, false);
+ list_for_each_entry_safe(desc, _desc, &list, desc_node) {
+ list_del_init(&desc->desc_node);
+ dwc_descriptor_free(dwc, desc, false);
+ }
return 0;
}
--
2.53.0
^ permalink raw reply [flat|nested] 8+ messages in thread* [PATCH v4 4/7] dmaengine: dw: calculate residue separately from completion
2026-10-29 22:29 [PATCH v4 0/7] dmaengine: dw: serialize completion and termination James Hilliard
` (2 preceding siblings ...)
2026-10-29 22:29 ` [PATCH v4 3/7] dmaengine: dw: complete cookies before releasing the channel lock James Hilliard
@ 2026-10-29 22:29 ` James Hilliard
2026-10-29 22:29 ` [PATCH v4 5/7] dmaengine: dw: drain the tasklet before releasing channel resources James Hilliard
` (2 subsequent siblings)
6 siblings, 0 replies; 8+ messages in thread
From: James Hilliard @ 2026-10-29 22:29 UTC (permalink / raw)
To: Viresh Kumar, Andy Shevchenko, Vinod Koul, Frank Li, Dan Williams
Cc: Serge Semin, Greg Kroah-Hartman, Jiri Slaby, Ilpo Järvinen,
dmaengine, linux-serial, linux-kernel, Sashiko,
Lars-Peter Clausen, James Hilliard, stable
From: Serge Semin <fancer.lancer@gmail.com>
The descriptor scanner mixes transfer-complete handling with hardware-LLP
residue calculation. A status query needs the latter for the requested
cookie even when no transfer-complete event is pending.
Move hardware-LLP residue calculation into its own helper and call it from
the status getter under the channel lock. Keep software-LLP progress in
the scanner and subtract the current block's progress when reporting its
residue. The scanner now handles transfer-complete events only, retaining
the distinction between zero source residue and destination completion.
Also search the queued descriptors so a transfer waiting to start reports
its full length instead of zero residue.
Fixes: 3bfb1d20b547 ("dmaengine: Driver for the Synopsys DesignWare DMA controller")
Cc: stable@vger.kernel.org
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
[james: retain polled completion and report queued residue]
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
Changelog RFC:
- Instead of just dropping the dwc_scan_descriptors() method invocation
calculate the residue in the Tx-status getter.
---
drivers/dma/dw/core.c | 166 +++++++++++++++++++++-----------------------------
1 file changed, 68 insertions(+), 98 deletions(-)
diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 1f7afcd01565..1d6419e1cd3c 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -274,123 +274,60 @@ static inline u32 dwc_get_sent(struct dw_dma_chan *dwc)
static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
{
- dma_addr_t llp;
struct dw_desc *desc, *_desc;
struct dw_desc *child;
- u32 status_xfer;
unsigned long flags;
LIST_HEAD(list);
spin_lock_irqsave(&dwc->lock, flags);
- llp = channel_readl(dwc, LLP);
- status_xfer = dma_readl(dw, RAW.XFER);
- if (status_xfer & dwc->mask) {
- /* Everything we've submitted is done */
- dma_writel(dw, CLEAR.XFER, dwc->mask);
- if (list_empty(&dwc->active_list)) {
- spin_unlock_irqrestore(&dwc->lock, flags);
- return;
- }
-
- if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
- struct list_head *head, *active = dwc->tx_node_active;
-
- /*
- * We are inside first active descriptor.
- * Otherwise something is really wrong.
- */
- desc = dwc_first_active(dwc);
-
- head = &desc->tx_list;
- if (active != head) {
- /* Update residue to reflect last sent descriptor */
- if (active == head->next)
- desc->residue -= desc->len;
- else
- desc->residue -= to_dw_desc(active->prev)->len;
-
- child = to_dw_desc(active);
+ if (!(dma_readl(dw, RAW.XFER) & dwc->mask))
+ goto unlock;
- /* Submit next block */
- dwc_do_single_block(dwc, child);
+ dma_writel(dw, CLEAR.XFER, dwc->mask);
+ if (list_empty(&dwc->active_list))
+ goto unlock;
- spin_unlock_irqrestore(&dwc->lock, flags);
- return;
- }
+ desc = dwc_first_active(dwc);
+ if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
+ struct list_head *head = &desc->tx_list;
+ struct list_head *active = dwc->tx_node_active;
- /* We are done here */
- clear_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags);
- }
+ if (active != head) {
+ /* Update residue to reflect last sent descriptor. */
+ if (active == head->next)
+ desc->residue -= desc->len;
+ else
+ desc->residue -= to_dw_desc(active->prev)->len;
- if (dma_readl(dw, CH_EN) & dwc->mask) {
- dev_err(chan2dev(&dwc->chan),
- "BUG: XFER bit set, but channel not idle!\n");
+ child = to_dw_desc(active);
- /* Try to continue after resetting the channel... */
- dwc_chan_disable(dw, dwc);
+ /* Submit next block, including for polled transfers. */
+ dwc_do_single_block(dwc, child);
+ goto unlock;
}
- /* Detach the completed transfer before starting queued work. */
- list_splice_init(&dwc->active_list, &list);
- list_for_each_entry(desc, &list, desc_node)
- dma_cookie_complete(&desc->txd);
- dwc_dostart_first_queued(dwc);
- spin_unlock_irqrestore(&dwc->lock, flags);
-
- list_for_each_entry_safe(desc, _desc, &list, desc_node) {
- list_del_init(&desc->desc_node);
- dwc_descriptor_free(dwc, desc, true);
- }
- return;
+ clear_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags);
}
- if (list_empty(&dwc->active_list)) {
- spin_unlock_irqrestore(&dwc->lock, flags);
- return;
- }
+ if (dma_readl(dw, CH_EN) & dwc->mask) {
+ dev_err(chan2dev(&dwc->chan),
+ "BUG: XFER bit set, but channel not idle!\n");
- if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
- dev_vdbg(chan2dev(&dwc->chan), "%s: soft LLP mode\n", __func__);
- spin_unlock_irqrestore(&dwc->lock, flags);
- return;
+ /* Try to continue after resetting the channel... */
+ dwc_chan_disable(dw, dwc);
}
- dev_vdbg(chan2dev(&dwc->chan), "%s: llp=%pad\n", __func__, &llp);
-
- list_for_each_entry_safe(desc, _desc, &dwc->active_list, desc_node) {
- /* Initial residue value */
- desc->residue = desc->total_len;
-
- /* Check first descriptors addr */
- if (desc->txd.phys == DWC_LLP_LOC(llp)) {
- spin_unlock_irqrestore(&dwc->lock, flags);
- return;
- }
-
- /* Check first descriptors llp */
- if (lli_read(desc, llp) == llp) {
- /* This one is currently in progress */
- desc->residue -= dwc_get_sent(dwc);
- spin_unlock_irqrestore(&dwc->lock, flags);
- return;
- }
-
- desc->residue -= desc->len;
- list_for_each_entry(child, &desc->tx_list, desc_node) {
- if (lli_read(child, llp) == llp) {
- /* Currently in progress */
- desc->residue -= dwc_get_sent(dwc);
- spin_unlock_irqrestore(&dwc->lock, flags);
- return;
- }
- desc->residue -= child->len;
- }
+ dma_cookie_complete(&desc->txd);
+ list_move_tail(&desc->desc_node, &list);
+ dwc_dostart_first_queued(dwc);
+unlock:
+ spin_unlock_irqrestore(&dwc->lock, flags);
+ list_for_each_entry_safe(desc, _desc, &list, desc_node) {
+ list_del_init(&desc->desc_node);
+ dwc_descriptor_free(dwc, desc, true);
}
-
- /* Residue describes source reads; only RAW.XFER completes a transfer. */
- spin_unlock_irqrestore(&dwc->lock, flags);
}
static inline void dwc_dump_lli(struct dw_dma_chan *dwc, struct dw_desc *desc)
@@ -969,9 +906,39 @@ static struct dw_desc *dwc_find_desc(struct dw_dma_chan *dwc, dma_cookie_t c)
if (desc->txd.cookie == c)
return desc;
+ list_for_each_entry(desc, &dwc->queue, desc_node)
+ if (desc->txd.cookie == c)
+ return desc;
+
return NULL;
}
+static u32 dwc_get_hard_llp_desc_residue(struct dw_dma_chan *dwc, struct dw_desc *desc)
+{
+ u32 residue = desc->total_len;
+ struct dw_desc *child;
+ dma_addr_t llp;
+
+ llp = channel_readl(dwc, LLP);
+
+ /* The first descriptor may still be waiting to be fetched. */
+ if (desc->txd.phys == DWC_LLP_LOC(llp))
+ return residue;
+
+ if (lli_read(desc, llp) == llp)
+ return residue - dwc_get_sent(dwc);
+
+ residue -= desc->len;
+ list_for_each_entry(child, &desc->tx_list, desc_node) {
+ if (lli_read(child, llp) == llp)
+ return residue - dwc_get_sent(dwc);
+
+ residue -= child->len;
+ }
+
+ return residue;
+}
+
static u32 dwc_get_residue_and_status(struct dw_dma_chan *dwc, dma_cookie_t cookie,
enum dma_status *status)
{
@@ -984,9 +951,12 @@ static u32 dwc_get_residue_and_status(struct dw_dma_chan *dwc, dma_cookie_t cook
desc = dwc_find_desc(dwc, cookie);
if (desc) {
if (desc == dwc_first_active(dwc)) {
- residue = desc->residue;
- if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags) && residue)
+ if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
+ residue = desc->residue;
residue -= dwc_get_sent(dwc);
+ } else {
+ residue = dwc_get_hard_llp_desc_residue(dwc, desc);
+ }
if (test_bit(DW_DMA_IS_PAUSED, &dwc->flags))
*status = DMA_PAUSED;
} else {
--
2.53.0
^ permalink raw reply [flat|nested] 8+ messages in thread* [PATCH v4 5/7] dmaengine: dw: drain the tasklet before releasing channel resources
2026-10-29 22:29 [PATCH v4 0/7] dmaengine: dw: serialize completion and termination James Hilliard
` (3 preceding siblings ...)
2026-10-29 22:29 ` [PATCH v4 4/7] dmaengine: dw: calculate residue separately from completion James Hilliard
@ 2026-10-29 22:29 ` James Hilliard
2026-10-29 22:29 ` [PATCH v4 6/7] dmaengine: dw: synchronize completion callbacks James Hilliard
2026-10-29 22:29 ` [PATCH v4 7/7] dmaengine: dw: Prevent tx-status calling DMA-desc callback James Hilliard
6 siblings, 0 replies; 8+ messages in thread
From: James Hilliard @ 2026-10-29 22:29 UTC (permalink / raw)
To: Viresh Kumar, Andy Shevchenko, Vinod Koul, Frank Li, Dan Williams
Cc: Serge Semin, Greg Kroah-Hartman, Jiri Slaby, Ilpo Järvinen,
dmaengine, linux-serial, linux-kernel, Sashiko,
Lars-Peter Clausen, James Hilliard, stable
The controller tasklet invokes callbacks after dropping the channel lock.
Releasing a channel can therefore clear its configuration and disable the
controller while that tasklet run is still using them.
Disable the tasklet before clearing channel resources and re-enable it
after updating the controller's in-use mask. This waits for an executing
run while preserving pending schedules for the other channels. Have a
pending run return before accessing registers when the last channel has
already been released.
Fixes: 3bfb1d20b547 ("dmaengine: Driver for the Synopsys DesignWare DMA controller")
Cc: stable@vger.kernel.org
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
drivers/dma/dw/core.c | 8 ++++++++
1 file changed, 8 insertions(+)
diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 1d6419e1cd3c..3bda85adbeee 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -398,6 +398,10 @@ static void dw_dma_tasklet(struct tasklet_struct *t)
u32 status_err;
unsigned int i;
+ /* Channel release may have drained a polled completion before this run. */
+ if (!dw->in_use)
+ return;
+
status_xfer = dma_readl(dw, RAW.XFER);
status_err = dma_readl(dw, RAW.ERROR);
@@ -1067,6 +1071,8 @@ static void dwc_free_chan_resources(struct dma_chan *chan)
struct dw_dma *dw = to_dw_dma(chan->device);
unsigned long flags;
+ tasklet_disable(&dw->tasklet);
+
dev_dbg(chan2dev(chan), "%s: descs allocated=%u\n", __func__,
dwc->descs_allocated);
@@ -1092,6 +1098,8 @@ static void dwc_free_chan_resources(struct dma_chan *chan)
if (!dw->in_use)
do_dw_dma_off(dw);
+ tasklet_enable(&dw->tasklet);
+
dev_vdbg(chan2dev(chan), "%s: done\n", __func__);
}
--
2.53.0
^ permalink raw reply [flat|nested] 8+ messages in thread* [PATCH v4 6/7] dmaengine: dw: synchronize completion callbacks
2026-10-29 22:29 [PATCH v4 0/7] dmaengine: dw: serialize completion and termination James Hilliard
` (4 preceding siblings ...)
2026-10-29 22:29 ` [PATCH v4 5/7] dmaengine: dw: drain the tasklet before releasing channel resources James Hilliard
@ 2026-10-29 22:29 ` James Hilliard
2026-10-29 22:29 ` [PATCH v4 7/7] dmaengine: dw: Prevent tx-status calling DMA-desc callback James Hilliard
6 siblings, 0 replies; 8+ messages in thread
From: James Hilliard @ 2026-10-29 22:29 UTC (permalink / raw)
To: Viresh Kumar, Andy Shevchenko, Vinod Koul, Frank Li, Dan Williams
Cc: Serge Semin, Greg Kroah-Hartman, Jiri Slaby, Ilpo Järvinen,
dmaengine, linux-serial, linux-kernel, Sashiko,
Lars-Peter Clausen, James Hilliard, stable, Frank Li
The controller tasklet can detach completed descriptors and invoke their
callbacks outside the channel lock. Terminating the channel does not wait
for those callbacks, and there is no device_synchronize hook. A client can
therefore reuse callback state or release its buffers after
dmaengine_synchronize() while an old callback still uses them.
Disable and re-enable the controller tasklet from device_synchronize,
outside the channel lock. Disabling waits for an executing tasklet,
including descriptors it already removed from the channel lists. After
termination, a later tasklet run cannot acquire another descriptor from
the terminated channel. Clients must continue to exclude new submissions
on that channel until synchronization finishes.
The tasklet is shared, so other channels may schedule it while this wait
is in progress. Preserve those pending runs: tasklet_kill() temporarily
owns the scheduling bit and can consume a concurrent scheduling request,
leaving controller interrupts masked. The disable/enable pair leaves the
scheduling bit and pending tasklet queue intact. Other channels' hardware
transfers continue, though their callbacks may be briefly deferred.
Fixes: b36f09c3c441 ("dmaengine: Add transfer termination synchronization support")
Reported-by: Sashiko <sashiko-bot@kernel.org>
Closes: https://lore.kernel.org/r/sashiko-outbox-180707@kernel.org
Cc: stable@vger.kernel.org
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
Reviewed-by: Frank Li <Frank.Li@nxp.com>
---
drivers/dma/dw/core.c | 14 ++++++++++++++
1 file changed, 14 insertions(+)
diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 3bda85adbeee..66065d7b26ae 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -902,6 +902,19 @@ static int dwc_terminate_all(struct dma_chan *chan)
return 0;
}
+static void dwc_synchronize(struct dma_chan *chan)
+{
+ struct dw_dma *dw = to_dw_dma(chan->device);
+
+ /*
+ * Termination removes the channel's descriptors from the lists, but a
+ * running tasklet may still own a completed descriptor and its callback.
+ * Wait for that run without losing schedules from the other channels.
+ */
+ tasklet_disable(&dw->tasklet);
+ tasklet_enable(&dw->tasklet);
+}
+
static struct dw_desc *dwc_find_desc(struct dw_dma_chan *dwc, dma_cookie_t c)
{
struct dw_desc *desc;
@@ -1295,6 +1308,7 @@ int do_dma_probe(struct dw_dma_chip *chip)
dw->dma.device_pause = dwc_pause;
dw->dma.device_resume = dwc_resume;
dw->dma.device_terminate_all = dwc_terminate_all;
+ dw->dma.device_synchronize = dwc_synchronize;
dw->dma.device_tx_status = dwc_tx_status;
dw->dma.device_issue_pending = dwc_issue_pending;
--
2.53.0
^ permalink raw reply [flat|nested] 8+ messages in thread* [PATCH v4 7/7] dmaengine: dw: Prevent tx-status calling DMA-desc callback
2026-10-29 22:29 [PATCH v4 0/7] dmaengine: dw: serialize completion and termination James Hilliard
` (5 preceding siblings ...)
2026-10-29 22:29 ` [PATCH v4 6/7] dmaengine: dw: synchronize completion callbacks James Hilliard
@ 2026-10-29 22:29 ` James Hilliard
6 siblings, 0 replies; 8+ messages in thread
From: James Hilliard @ 2026-10-29 22:29 UTC (permalink / raw)
To: Viresh Kumar, Andy Shevchenko, Vinod Koul, Frank Li, Dan Williams
Cc: Serge Semin, Greg Kroah-Hartman, Jiri Slaby, Ilpo Järvinen,
dmaengine, linux-serial, linux-kernel, Sashiko,
Lars-Peter Clausen, James Hilliard, stable
From: Serge Semin <fancer.lancer@gmail.com>
The DMA transfer status getter can invoke a completion callback from
dwc_scan_descriptors(). An 8250 RX timeout queries that status while
holding the UART port lock, and its DMA callback takes the same lock:
serial8250_handle_irq()
uart_port_lock_irqsave(port)
serial8250_rx_dma_flush()
dmaengine_tx_status()
dwc_scan_descriptors()
dwc_descriptor_free()
dma_rx_complete()
uart_port_lock_irqsave(port)
Queue completed descriptors on a channel completion list under the channel
lock. Let the controller tasklet detach that list and invoke callbacks
outside the lock. Termination discards notifications still on the shared
list; the tasklet owns descriptors it has already detached, and the
synchronization hook waits for that run.
Keep handling raw completion events from tx_status(). Clients such as
catpt poll transfers without DMA_PREP_INTERRUPT and can mask the controller
interrupt externally. Polling must still advance software-emulated LLP
blocks and complete cookies without waiting for tasklet execution. Hold
the channel lock across event handling and status calculation, then
schedule the tasklet for deferred notifications.
On channel release, discard queued notifications after draining the
tasklet, before clearing the controller's in-use state.
Fixes: 3bfb1d20b547 ("dmaengine: Driver for the Synopsys DesignWare DMA controller")
Cc: stable@vger.kernel.org
Signed-off-by: Serge Semin <fancer.lancer@gmail.com>
[james: defer notifications while preserving polled completion and cleanup]
Signed-off-by: James Hilliard <james.hilliard1@gmail.com>
---
Changelog RFC:
- Instead of just dropping the dwc_scan_descriptors() method invocation
calculate the residue in the Tx-status getter.
---
drivers/dma/dw/core.c | 111 ++++++++++++++++++++++++++++++--------------------
drivers/dma/dw/regs.h | 1 +
2 files changed, 68 insertions(+), 44 deletions(-)
diff --git a/drivers/dma/dw/core.c b/drivers/dma/dw/core.c
index 66065d7b26ae..d80be93f0c49 100644
--- a/drivers/dma/dw/core.c
+++ b/drivers/dma/dw/core.c
@@ -262,6 +262,22 @@ dwc_descriptor_free(struct dw_dma_chan *dwc, struct dw_desc *desc,
dmaengine_desc_callback_invoke(&cb, NULL);
}
+static void dwc_complete(struct dw_dma_chan *dwc)
+{
+ struct dw_desc *desc, *_desc;
+ unsigned long flags;
+ LIST_HEAD(list);
+
+ spin_lock_irqsave(&dwc->lock, flags);
+ list_splice_tail_init(&dwc->completed, &list);
+ spin_unlock_irqrestore(&dwc->lock, flags);
+
+ list_for_each_entry_safe(desc, _desc, &list, desc_node) {
+ list_del_init(&desc->desc_node);
+ dwc_descriptor_free(dwc, desc, true);
+ }
+}
+
/* Returns how many bytes were already received from source */
static inline u32 dwc_get_sent(struct dw_dma_chan *dwc)
{
@@ -274,19 +290,17 @@ static inline u32 dwc_get_sent(struct dw_dma_chan *dwc)
static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
{
- struct dw_desc *desc, *_desc;
+ struct dw_desc *desc;
struct dw_desc *child;
- unsigned long flags;
- LIST_HEAD(list);
- spin_lock_irqsave(&dwc->lock, flags);
+ lockdep_assert_held(&dwc->lock);
if (!(dma_readl(dw, RAW.XFER) & dwc->mask))
- goto unlock;
+ return;
dma_writel(dw, CLEAR.XFER, dwc->mask);
if (list_empty(&dwc->active_list))
- goto unlock;
+ return;
desc = dwc_first_active(dwc);
if (test_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags)) {
@@ -304,7 +318,7 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
/* Submit next block, including for polled transfers. */
dwc_do_single_block(dwc, child);
- goto unlock;
+ return;
}
clear_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags);
@@ -319,15 +333,8 @@ static void dwc_scan_descriptors(struct dw_dma *dw, struct dw_dma_chan *dwc)
}
dma_cookie_complete(&desc->txd);
- list_move_tail(&desc->desc_node, &list);
+ list_move_tail(&desc->desc_node, &dwc->completed);
dwc_dostart_first_queued(dwc);
-unlock:
- spin_unlock_irqrestore(&dwc->lock, flags);
-
- list_for_each_entry_safe(desc, _desc, &list, desc_node) {
- list_del_init(&desc->desc_node);
- dwc_descriptor_free(dwc, desc, true);
- }
}
static inline void dwc_dump_lli(struct dw_dma_chan *dwc, struct dw_desc *desc)
@@ -344,18 +351,17 @@ static void dwc_handle_error(struct dw_dma *dw, struct dw_dma_chan *dwc)
{
struct dw_desc *bad_desc;
struct dw_desc *child;
- unsigned long flags;
- spin_lock_irqsave(&dwc->lock, flags);
+ lockdep_assert_held(&dwc->lock);
/* Termination may have cleared the error since the tasklet sampled it. */
if (!(dma_readl(dw, RAW.ERROR) & dwc->mask))
- goto unlock;
+ return;
dwc_chan_disable(dw, dwc);
clear_bit(DW_DMA_IS_SOFT_LLP, &dwc->flags);
if (list_empty(&dwc->active_list))
- goto unlock;
+ return;
/*
* The descriptor currently at the head of the active list is
@@ -381,40 +387,41 @@ static void dwc_handle_error(struct dw_dma *dw, struct dw_dma_chan *dwc)
/* Pretend the descriptor completed successfully */
dma_cookie_complete(&bad_desc->txd);
- spin_unlock_irqrestore(&dwc->lock, flags);
+ list_add_tail(&bad_desc->desc_node, &dwc->completed);
+}
- dwc_descriptor_free(dwc, bad_desc, true);
- return;
+static void dwc_handle_channel(struct dw_dma *dw, struct dw_dma_chan *dwc)
+{
+ lockdep_assert_held(&dwc->lock);
-unlock:
- spin_unlock_irqrestore(&dwc->lock, flags);
+ if (dma_readl(dw, RAW.ERROR) & dwc->mask)
+ dwc_handle_error(dw, dwc);
+ else
+ dwc_scan_descriptors(dw, dwc);
}
static void dw_dma_tasklet(struct tasklet_struct *t)
{
struct dw_dma *dw = from_tasklet(dw, t, tasklet);
struct dw_dma_chan *dwc;
- u32 status_xfer;
- u32 status_err;
+ unsigned long flags;
unsigned int i;
+ u32 status;
/* Channel release may have drained a polled completion before this run. */
if (!dw->in_use)
return;
- status_xfer = dma_readl(dw, RAW.XFER);
- status_err = dma_readl(dw, RAW.ERROR);
-
- dev_vdbg(dw->dma.dev, "%s: status_err=%x\n", __func__, status_err);
+ status = dma_readl(dw, RAW.XFER) | dma_readl(dw, RAW.ERROR);
for (i = 0; i < dw->dma.chancnt; i++) {
dwc = &dw->chan[i];
- if (test_bit(DW_DMA_IS_CYCLIC, &dwc->flags))
- dev_vdbg(dw->dma.dev, "Cyclic xfer is not implemented\n");
- else if (status_err & (1 << i))
- dwc_handle_error(dw, dwc);
- else if (status_xfer & (1 << i))
- dwc_scan_descriptors(dw, dwc);
+ spin_lock_irqsave(&dwc->lock, flags);
+ /* The snapshot selects work; recheck events under the channel lock. */
+ if (status & dwc->mask)
+ dwc_handle_channel(dw, dwc);
+ spin_unlock_irqrestore(&dwc->lock, flags);
+ dwc_complete(dwc);
}
/* Re-enable interrupts */
@@ -890,6 +897,7 @@ static int dwc_terminate_all(struct dma_chan *chan)
list_splice_init(&dwc->active_list, &list);
list_for_each_entry(desc, &list, desc_node)
dma_cookie_complete(&desc->txd);
+ list_splice_init(&dwc->completed, &list);
spin_unlock_irqrestore(&dwc->lock, flags);
@@ -960,10 +968,9 @@ static u32 dwc_get_residue_and_status(struct dw_dma_chan *dwc, dma_cookie_t cook
enum dma_status *status)
{
struct dw_desc *desc;
- unsigned long flags;
u32 residue;
- spin_lock_irqsave(&dwc->lock, flags);
+ lockdep_assert_held(&dwc->lock);
desc = dwc_find_desc(dwc, cookie);
if (desc) {
@@ -983,7 +990,6 @@ static u32 dwc_get_residue_and_status(struct dw_dma_chan *dwc, dma_cookie_t cook
residue = 0;
}
- spin_unlock_irqrestore(&dwc->lock, flags);
return residue;
}
@@ -993,19 +999,26 @@ dwc_tx_status(struct dma_chan *chan,
struct dma_tx_state *txstate)
{
struct dw_dma_chan *dwc = to_dw_dma_chan(chan);
+ struct dw_dma *dw = to_dw_dma(chan->device);
enum dma_status ret;
+ unsigned long flags;
+ spin_lock_irqsave(&dwc->lock, flags);
ret = dma_cookie_status(chan, cookie, txstate);
if (ret == DMA_COMPLETE)
- return ret;
+ goto unlock;
- dwc_scan_descriptors(to_dw_dma(chan->device), dwc);
+ /* Poll completion even when the client has masked the controller IRQ. */
+ dwc_handle_channel(dw, dwc);
+ if (!list_empty(&dwc->completed))
+ tasklet_schedule(&dw->tasklet);
ret = dma_cookie_status(chan, cookie, txstate);
- if (ret == DMA_COMPLETE)
- return ret;
+ if (ret != DMA_COMPLETE)
+ dma_set_residue(txstate, dwc_get_residue_and_status(dwc, cookie, &ret));
- dma_set_residue(txstate, dwc_get_residue_and_status(dwc, cookie, &ret));
+unlock:
+ spin_unlock_irqrestore(&dwc->lock, flags);
return ret;
}
@@ -1082,8 +1095,11 @@ static void dwc_free_chan_resources(struct dma_chan *chan)
{
struct dw_dma_chan *dwc = to_dw_dma_chan(chan);
struct dw_dma *dw = to_dw_dma(chan->device);
+ struct dw_desc *desc, *_desc;
unsigned long flags;
+ LIST_HEAD(list);
+ /* Polled completion can leave descriptors waiting for the tasklet. */
tasklet_disable(&dw->tasklet);
dev_dbg(chan2dev(chan), "%s: descs allocated=%u\n", __func__,
@@ -1095,6 +1111,7 @@ static void dwc_free_chan_resources(struct dma_chan *chan)
BUG_ON(dma_readl(to_dw_dma(chan->device), CH_EN) & dwc->mask);
spin_lock_irqsave(&dwc->lock, flags);
+ list_splice_init(&dwc->completed, &list);
/* Clear custom channel configuration */
memset(&dwc->dws, 0, sizeof(struct dw_dma_slave));
@@ -1106,6 +1123,11 @@ static void dwc_free_chan_resources(struct dma_chan *chan)
spin_unlock_irqrestore(&dwc->lock, flags);
+ list_for_each_entry_safe(desc, _desc, &list, desc_node) {
+ list_del_init(&desc->desc_node);
+ dwc_descriptor_free(dwc, desc, false);
+ }
+
/* Disable controller in case it was a last user */
dw->in_use &= ~dwc->mask;
if (!dw->in_use)
@@ -1243,6 +1265,7 @@ int do_dma_probe(struct dw_dma_chip *chip)
INIT_LIST_HEAD(&dwc->active_list);
INIT_LIST_HEAD(&dwc->queue);
+ INIT_LIST_HEAD(&dwc->completed);
channel_clear_bit(dw, CH_EN, dwc->mask);
diff --git a/drivers/dma/dw/regs.h b/drivers/dma/dw/regs.h
index 5969d9cc8d7a..c41f18281efe 100644
--- a/drivers/dma/dw/regs.h
+++ b/drivers/dma/dw/regs.h
@@ -279,6 +279,7 @@ struct dw_dma_chan {
unsigned long flags;
struct list_head active_list;
struct list_head queue;
+ struct list_head completed;
unsigned int descs_allocated;
--
2.53.0
^ permalink raw reply [flat|nested] 8+ messages in thread