[PATCH net-next v4 0/3] net: ethernet: mtk_eth_soc: 9K jumbo frame support

[PATCH net-next v4 0/3] net: ethernet: mtk_eth_soc: 9K jumbo frame support

[Sandeep Haemoon]

This series makes the MediaTek SoC ethernet driver support 9K jumbo
frames on the 10G XGMII MACs (MT7988).  The driver advertises a 2030-byte
max_mtu and programs the MAC max-rx field for at most 2048 bytes, so
MTU > 2K is rejected and 9K frames are not usable.

Patch 1 fixes a pre-existing 36-bit DMA bug in mtk_poll_rx() that the
review of v3 found: a descriptor released without a new mapping is
handed back with the previous buffer's high address bits.  It is
independent of the rest of the series and carries a Fixes: tag for the
commit that introduced the bug, so the maintainers can route it to net
directly if they prefer.

Patch 2 gates the page_pool on the ring's descriptor length: the pool
hands out order-0 pages and maps at most MTK_PP_MAX_BUF_SIZE, so a ring
whose descriptor length is larger has to use the
netdev_alloc_frag()/mtk_max_buf_alloc() path.

Patch 3 adds the MTK_NETSYS_RX_9K capability, advertises 9K max_mtu on
the XGMII MACs (from the DT phy_mode at probe, so DSA can raise the
conduit MTU before the netdev is opened), programs XMAC_RX_CFG2 and the
PDMA RX SDL, derives the shared RX buffer length from the largest MTU,
sizes the RX rings from it and keeps the MAC max-rx limits in sync with
it.  A runtime MTU change that needs larger buffers is rejected with
-EBUSY while DMA is running; shrinking is allowed.  GMAC1, the built-in
switch port, keeps its MCR bucket programming (the largest the field
encodes is 2048), written after the MAC_MCR_FORCE_LINK_DOWN reset so it
survives every mac_config(); whether the internal switch path enforces
that field at all is a hardware property the commit message documents.

This work is a forward-port of the MediaTek downstream jumbo work: Mason
Chang's "change default rx buffer length" and "add 9k jumbo frame
support" (MediaTek OpenWrt feed 999-eth-30/31, carried in
frank-w/BPI-Router-Linux), plus Frank Wunderlich's "try to fix crash the
right way".  The runtime reallocation of Mason's "dynamic rx buffer
adjustment" (feed 999-eth-33) is not included and will be sent
separately.  Attribution is prose plus Link: tags: Co-developed-by
requires the original authors' own Signed-off-by lines, which we do not
have, and the port diverges from the downstream implementation (2K
buffer floor, per-ring pool gate, the -EBUSY rule, the XDP checks and
the truesize fix are not in the downstream patches).

The equivalent change was tested on a BPI-R4 Pro 8X (MT7988, 10G lan6 /
MxL86252) on the 6.18.60 backport: with both ends at MTU 9000, 8K ICMP
passes and iperf3 with MSS 8900 reaches ~9.87 Gbit/s (vs ~2.57 Gbit/s at
MSS 1460); the DSA conduit is raised to 9004 at boot.  This v7.3 series
is compile-tested with CONFIG_NET_MEDIATEK_SOC=y and COMPILE_TEST=y; no
hardware run of this exact tree yet.

Once any MAC's MTU needs more than ~3.5K, every RX buffer becomes a
16 KiB compound page; with the 9K ring size that pins around 64 MiB
while DMA is up and makes the refill a high-order GFP_ATOMIC
allocation.  That cost is inherent to the downstream design and is
called out in the commit message; skb->truesize now reports the
allocation that was actually made.

Changes in v4 (both v3 reviews, in full):

- XDP admission (High): the attach check now uses eth->rx_buf_len, the
  length the live rings were actually built with.  It is recomputed
  from the current MTUs whenever the rings are not live, or when the
  attach itself tears them down, so a program can neither attach while
  the rings have no page_pool nor be rejected on a closed device over a
  stale ring length; the dead dev->mtu clause in the same check is
  removed.
- the MAC max-rx rewrite in mtk_mac_config() and the new value in
  mtk_hw_init() are gated on MTK_NETSYS_RX_9K, so the other SoCs keep
  their per-device MCR buckets exactly as before this series.
- the PDMA RX SDL write is described as the new register write it is
  (the message no longer claims it replaces OR-ing).  The field layout
  (bits 16-30, frame length offset by MTK_PDMA_LRO_SDL) is the MediaTek
  downstream layout, validated on MT7988 hardware; the write is
  read-modify-write so every other RX_CFG bit keeps its value, and it
  now happens only in mtk_dma_init(), which runs at every DMA start.
- GMAC1 (the internal switch port) keeps its MCR bucket programming
  (largest encodable bucket is 2048); XMAC_RX_CFG2 is not used for it,
  matching the downstream reference.  The write in mtk_mac_config() now
  runs after the XGMII setup, whose MAC_MCR_FORCE_LINK_DOWN write is a
  full-register write that previously reset GMAC1's max-rx field back
  to the 1518 bucket on every mac_config().  Whether the internal path
  enforces the MCR field for switch-side 9K frames is a hardware
  property and is documented in the commit message: the downstream
  reference programs no limit for GMAC1 and jumbo frames pass the
  switch on the reference hardware, but if the field is enforced,
  switch-side frames above 2048 bytes are dropped and no driver write
  can lift that.
- XMAC_RX_CFG2 is always programmed from the shared buffer length
  (2K minimum), which includes 802.1Q headroom at every MTU, so the
  limit is the same value no matter which path ran last.
- skb->truesize reports the size of the compound page that was actually
  allocated, not the smaller frag_size.
- the -EBUSY rule's consequence for DSA (a user port MTU can only be
  raised with every MAC down) is now spelled out in the commit message.
- the stale comments above the pool gate and in mtk_dma_init() are
  rewritten to describe the code as it stands.
- patch 1/3 fixes the pre-existing 36-bit DMA descriptor corruption in
  mtk_poll_rx() found by the review of patch 1; it is small, sits in
  the file this series touches, and the introducing commit was
  identified upstream, so the Fixes: tag is included.
- patch 2/3 is retitled to say when the pool is skipped and its message
  no longer implies a frag_size gate existed before it.

Simon Horman's Reviewed-by is kept on patch 2 only: patches 1 and 3 are
new or changed materially since his review of v1.

Previous versions:
https://lore.kernel.org/all/patch-aad4cfa8d9522d1f7dbc9893ea12e813@loljews.com/ (v3)
https://lore.kernel.org/all/patch-2793186c653124c4c0b3d463bde2ea3a@loljews.com/ (v2)
https://lore.kernel.org/all/patch-4f863a941889f0bceca1c082f2d79624@loljews.com/ (v1)

Sandeep Haemoon (3):
  net: ethernet: mtk_eth_soc: reset RX DMA address each poll iteration
  net: ethernet: mtk_eth_soc: skip page_pool for RX rings whose buffers
    do not fit
  net: ethernet: mtk_eth_soc: add 9K jumbo frame support

 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 284 ++++++++++++++++----
 drivers/net/ethernet/mediatek/mtk_eth_soc.h |  12 +-
 2 files changed, 238 insertions(+), 58 deletions(-)

base-commit: c03c1a14507dfaf8b856c2608f9ac216021fc222
-- 
2.53.0

[PATCH net-next v4 1/3] net: ethernet: mtk_eth_soc: reset RX DMA

[Sandeep Haemoon]

mtk_poll_rx() keeps a single dma_addr_t across the whole loop and only
refreshes it when a replacement buffer was mapped for the descriptor
being processed.  The paths that jump straight to release_desc (no
netdev for the source port, MTK_RESETTING set, or a refill allocation
failure) then hand the descriptor back with the high address bits of the
buffer mapped for the previous descriptor, while the low bits in rxd1
still belong to the buffer the descriptor actually holds.

With MTK_36BIT_DMA and DRAM above 4 GiB the hardware then DMAs the next
frame to an address that is neither buffer, and the driver passes the
stale contents of the untouched buffer up the stack.

Reset dma_addr to DMA_MAPPING_ERROR at the start of every iteration, so
a descriptor that is released without a new mapping keeps its own high
address bits.

Fixes: 2d75891ebc09 ("net: ethernet: mtk_eth_soc: support 36-bit DMA addressing on MT7988")
Signed-off-by: Sandeep Haemoon <sandeeph@loljews.com>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index ad0fdc413..a46cf5441 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -2210,7 +2210,7 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
 	u8 *data, *new_data;
 	struct mtk_rx_dma_v2 *rxd, trxd;
 	int done = 0, bytes = 0;
-	dma_addr_t dma_addr = DMA_MAPPING_ERROR;
+	dma_addr_t dma_addr;
 	int ppe_idx = 0;
 
 	while (done < budget) {
@@ -2219,6 +2219,12 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
 		u32 hash, reason;
 		int mac = 0;
 
+		/* The release paths below hand the descriptor back with the
+		 * buffer it still holds, so only overwrite its address when
+		 * a new buffer was actually mapped for it.
+		 */
+		dma_addr = DMA_MAPPING_ERROR;
+
 		ring = mtk_get_rx_ring(eth);
 		if (unlikely(!ring))
 			goto rx_done;
-- 
2.53.0

[PATCH net-next v4 2/3] net: ethernet: mtk_eth_soc: skip page_pool

[Sandeep Haemoon]

The page_pool is created with order-0 pages and MTK_PP_MAX_BUF_SIZE as
the maximum DMA length, so it can only back a ring whose descriptor
length fits in that.

Gate the pool on ring->buf_size <= MTK_PP_MAX_BUF_SIZE and let larger
rings use the netdev_alloc_frag()/mtk_max_buf_alloc() path that already
exists.  ring->frag_size cannot serve as the limit: it follows the
netdev_alloc_frag() layout, whose headroom and skb_shared_info footprint
differ from the pool's, so a ring can have frag_size <= PAGE_SIZE while
its descriptor length is already larger than the pool can map.

With the current MTU limits every ring fits and the gate always passes;
it becomes active with the 9K jumbo support that follows, when the
shared rings grow past the limit.

Link: https://github.com/mediatek/mtk-openwrt-feeds
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Sandeep Haemoon <sandeeph@loljews.com>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 8 +++++++-
 1 file changed, 7 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index a46cf5441..6768ab8eb 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -2825,7 +2825,13 @@ static int mtk_rx_alloc(struct mtk_eth *eth, int ring_no, int rx_flag)
 	if (!ring->data)
 		return -ENOMEM;
 
-	if (mtk_page_pool_enabled(eth)) {
+	/* A page_pool hands out order-0 pages and is created with
+	 * MTK_PP_MAX_BUF_SIZE, so it can only back a ring whose descriptor
+	 * length fits.  Larger rings use the netdev_alloc_frag()/
+	 * mtk_max_buf_alloc() path below instead.
+	 */
+	if (mtk_page_pool_enabled(eth) &&
+	    ring->buf_size <= MTK_PP_MAX_BUF_SIZE) {
 		struct page_pool *pp;
 
 		pp = mtk_create_page_pool(eth, &ring->xdp_q, ring_no,
-- 
2.53.0

[PATCH net-next v4 3/3] net: ethernet: mtk_eth_soc: add 9K jumbo

[Sandeep Haemoon]

The driver caps max_mtu at 2030 bytes and programs the MAC max-rx field
for at most 2048-byte frames, so MTU > 2K is rejected and 9K jumbo
frames are not usable on the 10G XGMII MACs.

Add a MTK_NETSYS_RX_9K capability for MT7988 and:
- advertise 9K max_mtu on the XGMII MACs, from the DT phy_mode at probe
  time, so DSA can raise the conduit MTU before the netdev is opened;
- derive the shared RX buffer length from the largest MTU of any MAC,
  with a 2K minimum, and size the RX rings from it;
- program the PDMA RX SDL max-frame field from that length on netsys
  v3+.  The field stores the frame length offset by MTK_PDMA_LRO_SDL,
  the layout of the MediaTek downstream driver, and the DMA engine
  accepts frames only up to it, so without this new write frames above
  the small reset default (~1518 bytes) are dropped on the wire;
- program XMAC_RX_CFG2 from the same length on the XGMII MACs, keeping
  the bits outside the length field, so 802.1Q-tagged frames fit at any
  MTU.  GMAC1 (the built-in switch port, phy-mode internal) keeps its
  MCR bucket programming instead: the XMAC register is not used for it,
  and the MCR field only encodes up to 2048, so that is the largest
  limit the driver can program for it.  The write runs after the XGMII
  setup of mtk_mac_config(), whose MAC_MCR_FORCE_LINK_DOWN write is a
  full-register write that would otherwise reset the field to the 1518
  bucket.  Whether the internal switch path enforces the MCR field at
  all is a hardware property: the downstream reference programs no
  limit for GMAC1 and jumbo frames pass the switch on the reference
  hardware, which suggests the field is not enforced there, but if it
  is, switch-side frames above 2048 bytes are dropped and no driver
  write can lift that;
- rewrite the MAC limits on every successful mtk_mac_config() and on
  every mtk_hw_init() call on the SoCs with the capability, so no MAC
  accepts a frame the rings cannot hold, not even after a reopen with a
  smaller MTU.  The other SoCs keep their per-device limits: they never
  grow their rings, and their MCR buckets are left exactly as before
  this patch;
- reject a runtime MTU change that would need larger buffers while DMA
  is running (-EBUSY).  Shrinking is allowed: the rings keep the buffers
  they already have.  The rings are shared by every MAC, so raising a
  DSA user port MTU on a live system fails while any MAC is up; the
  runtime reallocation that lifts this is a separate series.

XDP runs only on rings that have a page_pool, and the pool cannot back
buffers larger than MTK_PP_MAX_BUF_SIZE, so an MTU that needs a larger
buffer cannot be combined with XDP.  Both the XDP attach and the MTU
change are rejected in that case.  The check uses eth->rx_buf_len, the
length the live rings were actually built with; when the rings are not
live, or the attach itself tears them down, the next open re-derives
the length from the current MTUs and that value is checked instead.  A
program can therefore never attach and silently not run, and an attach
on a closed device is never rejected over a stale ring length.

Once any MAC's MTU needs more than ~3.5K, every RX buffer is a 16 KiB
compound page: with the 9K ring size that pins around 64 MiB while DMA
is up and turns the refill into a high-order GFP_ATOMIC allocation.
skb->truesize then reports the size actually allocated for those
buffers, not the smaller frag_size.

This is a forward-port of the MediaTek downstream jumbo work: Mason
Chang's "change default rx buffer length" and "add 9k jumbo frame
support" (MediaTek OpenWrt feed 999-eth-30/31, carried in
frank-w/BPI-Router-Linux), plus Frank Wunderlich's "try to fix crash the
right way".  The runtime reallocation of Mason's "dynamic rx buffer
adjustment" (feed 999-eth-33) is not included; it will be sent
separately.

Link: https://github.com/frank-w/BPI-Router-Linux/commit/b4c6cb1d5532
Link: https://github.com/mediatek/mtk-openwrt-feeds
Signed-off-by: Sandeep Haemoon <sandeeph@loljews.com>
---
 drivers/net/ethernet/mediatek/mtk_eth_soc.c | 268 ++++++++++++++++----
 drivers/net/ethernet/mediatek/mtk_eth_soc.h |  12 +-
 2 files changed, 224 insertions(+), 56 deletions(-)

diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.c b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
index 6768ab8eb..527fdaeec 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.c
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.c
@@ -171,6 +171,7 @@ static const struct mtk_reg_map mt7988_reg_map = {
 		.glo_cfg	= 0x6a04,
 		.rst_idx	= 0x6a08,
 		.delay_irq	= 0x6a0c,
+		.rx_cfg		= 0x6a10,
 		.irq_status	= 0x6a20,
 		.irq_mask	= 0x6a28,
 		.adma_rx_dbg0	= 0x6a38,
@@ -554,6 +555,47 @@ static int mtk_mac_prepare(struct phylink_config *config, unsigned int mode,
 	return 0;
 }
 
+/* The MACs are fed from the shared RX rings, so the maximum frame they may
+ * accept is a property of the ring buffer length.  GMAC1 on netsys v3+ is
+ * the built-in switch port: it has no XMAC_RX_CFG2 limit register and its
+ * MCR field only encodes up to 2048, so it keeps the MCR bucket
+ * programming the other SoCs use.
+ */
+static void mtk_set_mcr_max_rx(struct mtk_mac *mac, u32 val)
+{
+	struct mtk_eth *eth = mac->hw;
+	u32 mcr_cur, mcr_new;
+
+	if (MTK_HAS_CAPS(eth->soc->caps, MTK_SOC_MT7628))
+		return;
+
+	if (!mtk_interface_mode_is_xgmii(eth, mac->interface) ||
+	    mac->id == MTK_GMAC1_ID) {
+		mcr_cur = mtk_r32(mac->hw, MTK_MAC_MCR(mac->id));
+		mcr_new = mcr_cur & ~MAC_MCR_MAX_RX_MASK;
+
+		if (val <= 1518)
+			mcr_new |= MAC_MCR_MAX_RX(MAC_MCR_MAX_RX_1518);
+		else if (val <= 1536)
+			mcr_new |= MAC_MCR_MAX_RX(MAC_MCR_MAX_RX_1536);
+		else if (val <= 1552)
+			mcr_new |= MAC_MCR_MAX_RX(MAC_MCR_MAX_RX_1552);
+		else
+			mcr_new |= MAC_MCR_MAX_RX(MAC_MCR_MAX_RX_2048);
+
+		if (mcr_new != mcr_cur)
+			mtk_w32(mac->hw, mcr_new, MTK_MAC_MCR(mac->id));
+	} else {
+		mcr_cur = mtk_r32(mac->hw, MTK_XMAC_RX_CFG2(mac->id));
+		mcr_new = mcr_cur & ~MTK_XMAC_MAX_RX_MASK;
+		mcr_new |= FIELD_PREP(MTK_XMAC_MAX_RX_MASK,
+				      min_t(u32, val, MTK_MAX_RX_LENGTH_9K));
+
+		if (mcr_new != mcr_cur)
+			mtk_w32(mac->hw, mcr_new, MTK_XMAC_RX_CFG2(mac->id));
+	}
+}
+
 static void mtk_mac_config(struct phylink_config *config, unsigned int mode,
 			   const struct phylink_link_state *state)
 {
@@ -678,6 +720,18 @@ static void mtk_mac_config(struct phylink_config *config, unsigned int mode,
 			mtk_setup_bridge_switch(eth);
 	}
 
+	/* On the SoCs with the 9K capability the rings grow with the MTU, so
+	 * rewrite the MAC limit on every successful mac_config, not only
+	 * when the interface mode changes: a reopen after an MTU change
+	 * must narrow the MACs that still carry the previous, larger
+	 * limit.  This must run after the XGMII setup above: its
+	 * MAC_MCR_FORCE_LINK_DOWN write is a full-register write that
+	 * would otherwise reset GMAC1's max-rx field (its limit lives in
+	 * the MCR register, not in XMAC_RX_CFG2) back to the 1518 bucket.
+	 */
+	if (MTK_HAS_CAPS(eth->soc->caps, MTK_NETSYS_RX_9K))
+		mtk_set_mcr_max_rx(mac, eth->rx_buf_len);
+
 	return;
 
 err_phy:
@@ -1242,22 +1296,22 @@ static void mtk_get_stats64(struct net_device *dev,
 	storage->tx_dropped = dev->stats.tx_dropped;
 }
 
-static inline int mtk_max_frag_size(int mtu)
+static inline int mtk_max_frag_size(struct mtk_eth *eth, int mtu)
 {
-	/* make sure buf_size will be at least MTK_MAX_RX_LENGTH */
-	if (mtu + MTK_RX_ETH_HLEN < MTK_MAX_RX_LENGTH_2K)
-		mtu = MTK_MAX_RX_LENGTH_2K - MTK_RX_ETH_HLEN;
+	/* make sure buf_size will be at least the shared rx buffer length */
+	if (mtu + MTK_RX_ETH_HLEN < eth->rx_buf_len)
+		mtu = eth->rx_buf_len - MTK_RX_ETH_HLEN;
 
 	return SKB_DATA_ALIGN(MTK_RX_HLEN + mtu) +
 		SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 }
 
-static inline int mtk_max_buf_size(int frag_size)
+static inline int mtk_max_buf_size(struct mtk_eth *eth, int frag_size)
 {
 	int buf_size = frag_size - NET_SKB_PAD - NET_IP_ALIGN -
 		       SKB_DATA_ALIGN(sizeof(struct skb_shared_info));
 
-	WARN_ON(buf_size < MTK_MAX_RX_LENGTH_2K);
+	WARN_ON(buf_size < eth->rx_buf_len);
 
 	return buf_size;
 }
@@ -1280,9 +1334,17 @@ static bool mtk_rx_get_desc(struct mtk_eth *eth, struct mtk_rx_dma_v2 *rxd,
 	return true;
 }
 
-static void *mtk_max_lro_buf_alloc(gfp_t gfp_mask)
+/* mtk_max_buf_alloc() rounds the buffer up to a whole page order, so
+ * report the size it actually allocated, not the smaller frag_size, in
+ * skb->truesize.
+ */
+static unsigned int mtk_buf_alloc_size(unsigned int size)
+{
+	return PAGE_SIZE << get_order(size);
+}
+
+static void *mtk_max_buf_alloc(unsigned int size, gfp_t gfp_mask)
 {
-	unsigned int size = mtk_max_frag_size(MTK_MAX_LRO_RX_LENGTH);
 	unsigned long data;
 
 	data = __get_free_pages(gfp_mask | __GFP_COMP | __GFP_NOWARN,
@@ -2313,10 +2375,15 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
 				skb_metadata_set(skb, metasize);
 			skb_mark_for_recycle(skb);
 		} else {
+			unsigned int alloc_size = ring->frag_size > PAGE_SIZE ?
+				mtk_buf_alloc_size(ring->frag_size) :
+				ring->frag_size;
+
 			if (ring->frag_size <= PAGE_SIZE)
 				new_data = napi_alloc_frag(ring->frag_size);
 			else
-				new_data = mtk_max_lro_buf_alloc(GFP_ATOMIC);
+				new_data = mtk_max_buf_alloc(ring->frag_size,
+							     GFP_ATOMIC);
 
 			if (unlikely(!new_data)) {
 				netdev->stats.rx_dropped++;
@@ -2339,7 +2406,7 @@ static int mtk_poll_rx(struct napi_struct *napi, int budget,
 			dma_unmap_single(eth->dma_dev, ((u64)trxd.rxd1 | addr64),
 					 ring->buf_size, DMA_FROM_DEVICE);
 
-			skb = build_skb(data, ring->frag_size);
+			skb = build_skb(data, alloc_size);
 			if (unlikely(!skb)) {
 				netdev->stats.rx_dropped++;
 				skb_free_frag(data);
@@ -2818,8 +2885,8 @@ static int mtk_rx_alloc(struct mtk_eth *eth, int ring_no, int rx_flag)
 		rx_dma_size = soc->rx.dma_size;
 	}
 
-	ring->frag_size = mtk_max_frag_size(rx_data_len);
-	ring->buf_size = mtk_max_buf_size(ring->frag_size);
+	ring->frag_size = mtk_max_frag_size(eth, rx_data_len);
+	ring->buf_size = mtk_max_buf_size(eth, ring->frag_size);
 	ring->data = kcalloc(rx_dma_size, sizeof(*ring->data),
 			     GFP_KERNEL);
 	if (!ring->data)
@@ -2864,7 +2931,8 @@ static int mtk_rx_alloc(struct mtk_eth *eth, int ring_no, int rx_flag)
 			if (ring->frag_size <= PAGE_SIZE)
 				data = netdev_alloc_frag(ring->frag_size);
 			else
-				data = mtk_max_lro_buf_alloc(GFP_KERNEL);
+				data = mtk_max_buf_alloc(ring->frag_size,
+							 GFP_KERNEL);
 
 			if (!data)
 				return -ENOMEM;
@@ -3260,6 +3328,56 @@ static int mtk_dma_busy_wait(struct mtk_eth *eth)
 	return ret;
 }
 
+static int mtk_max_gmac_mtu(struct mtk_eth *eth)
+{
+	int i, max_mtu = ETH_DATA_LEN;
+
+	for (i = 0; i < ARRAY_SIZE(eth->netdev); i++)
+		if (eth->netdev[i] && eth->netdev[i]->mtu > max_mtu)
+			max_mtu = eth->netdev[i]->mtu;
+
+	return max_mtu;
+}
+
+static u32 mtk_rx_buf_len_from_mtu(int max_mtu)
+{
+	int length = max_mtu + MTK_RX_ETH_HLEN;
+
+	if (length <= MTK_MAX_RX_LENGTH_2K)
+		return MTK_MAX_RX_LENGTH_2K;
+
+	return DIV_ROUND_UP(length, 1024) * 1024;
+}
+
+/* The rx rings are shared by every MAC, so their buffers are sized for
+ * the largest MTU configured on any of them.
+ */
+static u32 mtk_rx_buf_len(struct mtk_eth *eth)
+{
+	return mtk_rx_buf_len_from_mtu(mtk_max_gmac_mtu(eth));
+}
+
+/* Program the PDMA RX max-frame (SDL) field from the shared RX buffer
+ * length.  The field only exists on netsys v3+ and stores the frame
+ * length offset by MTK_PDMA_LRO_SDL, the layout used by the MediaTek
+ * downstream driver; the DMA engine accepts frames only up to it, so
+ * without this write jumbo frames are dropped.
+ */
+static void mtk_pdma_set_sdl(struct mtk_eth *eth)
+{
+	const struct mtk_reg_map *reg_map = eth->soc->reg_map;
+	u32 val;
+
+	if (!mtk_is_netsys_v3_or_greater(eth))
+		return;
+
+	val = mtk_r32(eth, reg_map->pdma.rx_cfg);
+	val &= ~MTK_RX_CFG_SDL_MASK;
+	val |= FIELD_PREP(MTK_RX_CFG_SDL_MASK,
+			  MTK_PDMA_LRO_SDL + eth->rx_buf_len);
+	mtk_w32(eth, val, reg_map->pdma.rx_cfg);
+}
+
 static int mtk_dma_init(struct mtk_eth *eth)
 {
 	int err;
@@ -3268,6 +3386,14 @@ static int mtk_dma_init(struct mtk_eth *eth)
 	if (mtk_dma_busy_wait(eth))
 		return -EBUSY;
 
+	/* Derived here, at ring allocation, so eth->rx_buf_len always
+	 * describes the buffers the rings actually hold; mtk_change_mtu()
+	 * updates it while DMA is down so it describes the rings-to-be,
+	 * and mtk_mac_config() then never lets a MAC accept a frame the
+	 * rings cannot take.
+	 */
+	eth->rx_buf_len = mtk_rx_buf_len(eth);
+
 	if (MTK_HAS_CAPS(eth->soc->caps, MTK_QDMA)) {
 		/* QDMA needs scratch memory for internal reordering of the
 		 * descriptors
@@ -3311,6 +3437,8 @@ static int mtk_dma_init(struct mtk_eth *eth)
 		mtk_w32(eth, 0x0, eth->soc->reg_map->qdma.hred);
 	}
 
+	mtk_pdma_set_sdl(eth);
+
 	return 0;
 }
 
@@ -3601,17 +3729,6 @@ static int mtk_device_event(struct notifier_block *n, unsigned long event, void
 	return NOTIFY_DONE;
 }
 
-static int mtk_max_gmac_mtu(struct mtk_eth *eth)
-{
-	int i, max_mtu = ETH_DATA_LEN;
-
-	for (i = 0; i < ARRAY_SIZE(eth->netdev); i++)
-		if (eth->netdev[i] && eth->netdev[i]->mtu > max_mtu)
-			max_mtu = eth->netdev[i]->mtu;
-
-	return max_mtu;
-}
-
 static int mtk_open(struct net_device *dev)
 {
 	struct mtk_mac *mac = netdev_priv(dev);
@@ -3781,6 +3898,7 @@ static int mtk_xdp_setup(struct net_device *dev, struct bpf_prog *prog,
 	struct mtk_mac *mac = netdev_priv(dev);
 	struct mtk_eth *eth = mac->hw;
 	struct bpf_prog *old_prog;
+	u32 rx_buf_len;
 	bool need_update;
 
 	if (eth->hwlro) {
@@ -3788,12 +3906,26 @@ static int mtk_xdp_setup(struct net_device *dev, struct bpf_prog *prog,
 		return -EOPNOTSUPP;
 	}
 
-	if (dev->mtu > MTK_PP_MAX_BUF_SIZE) {
+	need_update = !!eth->prog != !!prog;
+
+	/* XDP only runs on rings that have a page_pool, and the pool is
+	 * only created when the shared RX buffer length fits
+	 * MTK_PP_MAX_BUF_SIZE.  eth->rx_buf_len describes the live rings;
+	 * when the rings are not live, or this operation tears them down,
+	 * the next open re-derives it from the current MTUs, so check
+	 * that value instead.
+	 */
+	rx_buf_len = eth->rx_buf_len;
+	if (!refcount_read(&eth->dma_refcnt) ||
+	    (netif_running(dev) && need_update &&
+	     refcount_read(&eth->dma_refcnt) == 1))
+		rx_buf_len = mtk_rx_buf_len(eth);
+
+	if (rx_buf_len > MTK_PP_MAX_BUF_SIZE) {
 		NL_SET_ERR_MSG_MOD(extack, "MTU too large for XDP");
 		return -EOPNOTSUPP;
 	}
 
-	need_update = !!eth->prog != !!prog;
 	if (netif_running(dev) && need_update)
 		mtk_stop(dev);
 
@@ -3928,30 +4060,6 @@ static void mtk_dim_tx(struct work_struct *work)
 	dim->state = DIM_START_MEASURE;
 }
 
-static void mtk_set_mcr_max_rx(struct mtk_mac *mac, u32 val)
-{
-	struct mtk_eth *eth = mac->hw;
-	u32 mcr_cur, mcr_new;
-
-	if (MTK_HAS_CAPS(eth->soc->caps, MTK_SOC_MT7628))
-		return;
-
-	mcr_cur = mtk_r32(mac->hw, MTK_MAC_MCR(mac->id));
-	mcr_new = mcr_cur & ~MAC_MCR_MAX_RX_MASK;
-
-	if (val <= 1518)
-		mcr_new |= MAC_MCR_MAX_RX(MAC_MCR_MAX_RX_1518);
-	else if (val <= 1536)
-		mcr_new |= MAC_MCR_MAX_RX(MAC_MCR_MAX_RX_1536);
-	else if (val <= 1552)
-		mcr_new |= MAC_MCR_MAX_RX(MAC_MCR_MAX_RX_1552);
-	else
-		mcr_new |= MAC_MCR_MAX_RX(MAC_MCR_MAX_RX_2048);
-
-	if (mcr_new != mcr_cur)
-		mtk_w32(mac->hw, mcr_new, MTK_MAC_MCR(mac->id));
-}
-
 static void mtk_hw_reset(struct mtk_eth *eth)
 {
 	u32 val;
@@ -4219,8 +4327,11 @@ static int mtk_hw_init(struct mtk_eth *eth, bool reset)
 			continue;
 
 		mtk_w32(eth, MAC_MCR_FORCE_LINK_DOWN, MTK_MAC_MCR(i));
-		mtk_set_mcr_max_rx(netdev_priv(dev),
-				   dev->mtu + MTK_RX_ETH_HLEN);
+		if (MTK_HAS_CAPS(eth->soc->caps, MTK_NETSYS_RX_9K))
+			mtk_set_mcr_max_rx(netdev_priv(dev), eth->rx_buf_len);
+		else
+			mtk_set_mcr_max_rx(netdev_priv(dev),
+					   dev->mtu + MTK_RX_ETH_HLEN);
 	}
 
 	/* Indicates CDM to parse the MTK special tag from CPU
@@ -4361,21 +4472,59 @@ static int mtk_change_mtu(struct net_device *dev, int new_mtu)
 	int length = new_mtu + MTK_RX_ETH_HLEN;
 	struct mtk_mac *mac = netdev_priv(dev);
 	struct mtk_eth *eth = mac->hw;
+	u32 rx_buf_len;
+	bool running;
 	int max_mtu, i;
 
+	/* The RX rings are shared by every MAC, so the buffer length
+	 * follows the largest MTU of all of them, the new one included.
+	 */
+	max_mtu = new_mtu;
+	for (i = 0; i < MTK_MAX_DEVS; i++) {
+		if (eth->netdev[i] && eth->netdev[i] != dev &&
+		    eth->netdev[i]->mtu > max_mtu)
+			max_mtu = eth->netdev[i]->mtu;
+	}
+	rx_buf_len = mtk_rx_buf_len_from_mtu(max_mtu);
+
 	if (rcu_access_pointer(eth->prog) &&
-	    length > MTK_PP_MAX_BUF_SIZE) {
+	    rx_buf_len > MTK_PP_MAX_BUF_SIZE) {
 		netdev_err(dev, "Invalid MTU for XDP mode\n");
 		return -EINVAL;
 	}
 
-	mtk_set_mcr_max_rx(mac, length);
+	/* The rings cannot be resized in place while DMA is running: a
+	 * larger buffer can only come from the reallocation at the next
+	 * open, so reject it.  A smaller one is fine, the buffers the
+	 * rings already hold are big enough for it.
+	 */
+	running = refcount_read(&eth->dma_refcnt);
+	if (running && rx_buf_len > eth->rx_buf_len)
+		return -EBUSY;
+
+	/* On the SoCs whose rings grow with the MTU, keep the MAC limit in
+	 * step with the shared buffers; the other SoCs keep the per-device
+	 * limit they always had.
+	 */
+	if (MTK_HAS_CAPS(eth->soc->caps, MTK_NETSYS_RX_9K))
+		mtk_set_mcr_max_rx(mac, rx_buf_len);
+	else
+		mtk_set_mcr_max_rx(mac, length);
+
 	WRITE_ONCE(dev->mtu, new_mtu);
 
 	max_mtu = mtk_max_gmac_mtu(eth);
 	for (i = 0; i < ARRAY_SIZE(eth->ppe); i++)
 		mtk_ppe_update_mtu(eth->ppe[i], max_mtu);
 
+	/* While DMA is up the rings keep the buffers they were built
+	 * with; update eth->rx_buf_len only when DMA is down so it keeps
+	 * describing the buffers the rings hold, or will hold at the next
+	 * open.
+	 */
+	if (!running)
+		eth->rx_buf_len = rx_buf_len;
+
 	return 0;
 }
 
@@ -5021,8 +5170,17 @@ static int mtk_add_mac(struct mtk_eth *eth, struct device_node *np)
 	eth->netdev[id]->irq = eth->irq[MTK_FE_IRQ_SHARED];
 	eth->netdev[id]->dev.of_node = np;
 
+	/* DSA sets the conduit MTU (user MTU + tag) before the netdev is
+	 * opened, so max_mtu must already be final here.  Deriving it only
+	 * in mtk_open() leaves the conduit at its 1504 default and blocks
+	 * 9K frames on the DSA user ports.
+	 */
 	if (MTK_HAS_CAPS(eth->soc->caps, MTK_SOC_MT7628))
 		eth->netdev[id]->max_mtu = MTK_MAX_RX_LENGTH - MTK_RX_ETH_HLEN;
+	else if (MTK_HAS_CAPS(eth->soc->caps, MTK_NETSYS_RX_9K) &&
+		 mtk_interface_mode_is_xgmii(eth, phy_mode))
+		eth->netdev[id]->max_mtu =
+			MTK_MAX_RX_LENGTH_9K - MTK_RX_ETH_HLEN;
 	else
 		eth->netdev[id]->max_mtu = MTK_MAX_RX_LENGTH_2K - MTK_RX_ETH_HLEN;
 
@@ -5163,6 +5321,8 @@ static int mtk_probe(struct platform_device *pdev)
 	spin_lock_init(&eth->rx_irq_lock);
 	spin_lock_init(&eth->dim_lock);
 
+	eth->rx_buf_len = MTK_MAX_RX_LENGTH_2K;
+
 	eth->rx_dim.mode = DIM_CQ_PERIOD_MODE_START_FROM_EQE;
 	INIT_WORK(&eth->rx_dim.work, mtk_dim_rx);
 	INIT_DELAYED_WORK(&eth->reset.monitor_work, mtk_hw_reset_monitor_work);
diff --git a/drivers/net/ethernet/mediatek/mtk_eth_soc.h b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
index 88a9b3b23..6525fcc5c 100644
--- a/drivers/net/ethernet/mediatek/mtk_eth_soc.h
+++ b/drivers/net/ethernet/mediatek/mtk_eth_soc.h
@@ -29,6 +29,7 @@
 #define MTK_QDMA_PAGE_SIZE	2048
 #define MTK_MAX_RX_LENGTH	1536
 #define MTK_MAX_RX_LENGTH_2K	2048
+#define MTK_MAX_RX_LENGTH_9K	9216
 #define MTK_TX_DMA_BUF_LEN	0x3fff
 #define MTK_TX_DMA_BUF_LEN_V2	0xffff
 #define MTK_QDMA_RING_SIZE	2048
@@ -198,9 +199,10 @@
 #define MTK_MULTI_EN		BIT(10)
 #define MTK_PDMA_SIZE_8DWORDS	(1 << 4)
 
-/* PDMA Global Configuration Register */
+/* PDMA RX Configuration Register */
 #define MTK_PDMA_LRO_SDL	0x3000
 #define MTK_RX_CFG_SDL_OFFSET	16
+#define MTK_RX_CFG_SDL_MASK	GENMASK(30, MTK_RX_CFG_SDL_OFFSET)
 
 /* PDMA Reset Index Register */
 #define MTK_PST_DRX_IDX0	BIT(16)
@@ -530,6 +532,8 @@
 /* XFI Mac control registers */
 #define MTK_XMAC_BASE(x)	(0x12000 + (((x) - 1) * 0x1000))
 #define MTK_XMAC_MCR(x)		(MTK_XMAC_BASE(x))
+#define MTK_XMAC_RX_CFG2(x)	(MTK_XMAC_MCR(x) + 0xd0)
+#define MTK_XMAC_MAX_RX_MASK	GENMASK(13, 0)
 #define XMAC_MCR_TRX_DISABLE	0xf
 #define XMAC_MCR_FORCE_TX_FC	BIT(5)
 #define XMAC_MCR_FORCE_RX_FC	BIT(4)
@@ -985,6 +989,7 @@ enum mkt_eth_capabilities {
 	MTK_INFRA_BIT,
 	MTK_SHARED_SGMII_BIT,
 	MTK_HWLRO_BIT,
+	MTK_NETSYS_RX_9K_BIT,
 	MTK_SHARED_INT_BIT,
 	MTK_TRGMII_MT7621_CLK_BIT,
 	MTK_QDMA_BIT,
@@ -1026,6 +1031,7 @@ enum mkt_eth_capabilities {
 #define MTK_INFRA		BIT_ULL(MTK_INFRA_BIT)
 #define MTK_SHARED_SGMII	BIT_ULL(MTK_SHARED_SGMII_BIT)
 #define MTK_HWLRO		BIT_ULL(MTK_HWLRO_BIT)
+#define MTK_NETSYS_RX_9K	BIT_ULL(MTK_NETSYS_RX_9K_BIT)
 #define MTK_SHARED_INT		BIT_ULL(MTK_SHARED_INT_BIT)
 #define MTK_TRGMII_MT7621_CLK	BIT_ULL(MTK_TRGMII_MT7621_CLK_BIT)
 #define MTK_QDMA		BIT_ULL(MTK_QDMA_BIT)
@@ -1127,7 +1133,7 @@ enum mkt_eth_capabilities {
 
 #define MT7988_CAPS  (MTK_36BIT_DMA | MTK_GDM1_ESW | MTK_GMAC2_2P5GPHY | \
 		      MTK_MUX_GMAC2_TO_2P5GPHY | MTK_QDMA | MTK_RSTCTRL_PPE1 | \
-		      MTK_RSTCTRL_PPE2 | MTK_SRAM)
+		      MTK_RSTCTRL_PPE2 | MTK_SRAM | MTK_NETSYS_RX_9K)
 
 struct mtk_tx_dma_desc_info {
 	dma_addr_t	addr;
@@ -1151,6 +1157,7 @@ struct mtk_reg_map {
 		u32	glo_cfg;	/* global configuration */
 		u32	rst_idx;	/* reset index */
 		u32	delay_irq;	/* delay interrupt */
+		u32	rx_cfg;		/* rx dma configuration */
 		u32	irq_status;	/* interrupt status */
 		u32	irq_mask;	/* interrupt mask */
 		u32	adma_rx_dbg0;
@@ -1314,6 +1321,7 @@ struct mtk_eth {
 	struct mtk_tx_ring		tx_ring;
 	struct mtk_rx_ring		rx_ring[MTK_MAX_RX_RING_NUM];
 	struct mtk_rx_ring		rx_ring_qdma;
+	u32				rx_buf_len;
 	struct napi_struct		tx_napi;
 	struct napi_struct		rx_napi;
 	void				*scratch_ring;
-- 
2.53.0