[PATCH 1/2] dmaengine: dma-axi-dmac: Defer freeing DMA descriptors

["Nuno Sá via B4 Relay" <devnull+nuno.sa.analog.com@kernel.org>]

From: Eliza Balas <eliza.balas@analog.com>

This IP core can be used in architectures (like Microblaze) where DMA
descriptors are allocated with vmalloc(). Hence, given that freeing the
descriptors happen in softirq context, vunmpap() will BUG().

To solve the above, we setup a work item during allocation of the
descriptors and schedule in softirq context. Hence, the actual freeing
happens in threaded context.

Signed-off-by: Eliza Balas <eliza.balas@analog.com>
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
---
 drivers/dma/dma-axi-dmac.c | 48 +++++++++++++++++++++++++++++++++-------------
 1 file changed, 35 insertions(+), 13 deletions(-)

diff --git a/drivers/dma/dma-axi-dmac.c b/drivers/dma/dma-axi-dmac.c
index 45c2c8e4bc45..df2668064ea2 100644
--- a/drivers/dma/dma-axi-dmac.c
+++ b/drivers/dma/dma-axi-dmac.c
@@ -133,6 +133,8 @@ struct axi_dmac_desc {
 	struct virt_dma_desc vdesc;
 	struct axi_dmac_chan *chan;
 
+	struct work_struct sched_work;
+
 	bool cyclic;
 	bool cyclic_eot;
 	bool have_partial_xfer;
@@ -650,6 +652,26 @@ static void axi_dmac_issue_pending(struct dma_chan *c)
 	spin_unlock_irqrestore(&chan->vchan.lock, flags);
 }
 
+static void axi_dmac_free_desc(struct axi_dmac_desc *desc)
+{
+	struct axi_dmac *dmac = chan_to_axi_dmac(desc->chan);
+	struct device *dev = dmac->dma_dev.dev;
+	struct axi_dmac_hw_desc *hw = desc->sg[0].hw;
+	dma_addr_t hw_phys = desc->sg[0].hw_phys;
+
+	dma_free_coherent(dev, PAGE_ALIGN(desc->num_sgs * sizeof(*hw)),
+			  hw, hw_phys);
+	kfree(desc);
+}
+
+static void axi_dmac_free_desc_schedule_work(struct work_struct *work)
+{
+	struct axi_dmac_desc *desc = container_of(work, struct axi_dmac_desc,
+						  sched_work);
+
+	axi_dmac_free_desc(desc);
+}
+
 static struct axi_dmac_desc *
 axi_dmac_alloc_desc(struct axi_dmac_chan *chan, unsigned int num_sgs)
 {
@@ -687,21 +709,18 @@ axi_dmac_alloc_desc(struct axi_dmac_chan *chan, unsigned int num_sgs)
 	/* The last hardware descriptor will trigger an interrupt */
 	desc->sg[num_sgs - 1].hw->flags = AXI_DMAC_HW_FLAG_LAST | AXI_DMAC_HW_FLAG_IRQ;
 
+	/*
+	 * We need to setup a work item because this IP can be used on archs
+	 * that rely on vmalloced memory for descriptors. And given that freeing
+	 * the descriptors happens in softirq context, vunmpap() will BUG().
+	 * Hence, setup the worker so that we can queue it and free the
+	 * descriptor in threaded context.
+	 */
+	INIT_WORK(&desc->sched_work, axi_dmac_free_desc_schedule_work);
+
 	return desc;
 }
 
-static void axi_dmac_free_desc(struct axi_dmac_desc *desc)
-{
-	struct axi_dmac *dmac = chan_to_axi_dmac(desc->chan);
-	struct device *dev = dmac->dma_dev.dev;
-	struct axi_dmac_hw_desc *hw = desc->sg[0].hw;
-	dma_addr_t hw_phys = desc->sg[0].hw_phys;
-
-	dma_free_coherent(dev, PAGE_ALIGN(desc->num_sgs * sizeof(*hw)),
-			  hw, hw_phys);
-	kfree(desc);
-}
-
 static struct axi_dmac_sg *axi_dmac_fill_linear_sg(struct axi_dmac_chan *chan,
 	enum dma_transfer_direction direction, dma_addr_t addr,
 	unsigned int num_periods, unsigned int period_len,
@@ -942,7 +961,10 @@ static void axi_dmac_free_chan_resources(struct dma_chan *c)
 
 static void axi_dmac_desc_free(struct virt_dma_desc *vdesc)
 {
-	axi_dmac_free_desc(to_axi_dmac_desc(vdesc));
+	struct axi_dmac_desc *desc = to_axi_dmac_desc(vdesc);
+
+	/* See the comment in axi_dmac_alloc_desc() for the why! */
+	schedule_work(&desc->sched_work);
 }
 
 static bool axi_dmac_regmap_rdwr(struct device *dev, unsigned int reg)

-- 
2.53.0