[PATCH] wifi: rtw88: sdio: Honor the host max_req_size in the RX path

[Martin Blumenstingl]

Lukas reports skb_over_panic errors on his Banana Pi BPI-CM4 which comes
with an Amlogic A311D (G12B) SoC and a RTL8822CS SDIO wifi/Bluetooth
combo card. The error he observed is identical to what has been fixed
in commit e967229ead0e ("wifi: rtw88: sdio: Check the HISR RX_REQUEST
bit in rtw_sdio_rx_isr()") but that commit didn't fix Lukas' problem.

Lukas found that disabling or limiting RX aggregation fix the problem
for him. In the following discussion a few key topics have been
discussed which have an impact on this problem:
- The Amlogic A311D (G12B) SoC has a hardware bug in the SDIO controller
  which prevents DMA transfers. Instead all transfers need to go through
  the controller SRAM which limits transfers to 1536 bytes
- rtw88 chips don't split incoming (RX) packets, so if a big packet is
  received this is forwarded to the host in it's original form
- rtw88 chips can do RX aggregation, meaning more multiple incoming
  packets can be pulled by the host from the card with one MMC/SDIO
  transfer. This Depends on settings in the REG_RXDMA_AGG_PG_TH
  register (BIT_RXDMA_AGG_PG_TH limits the number of packets that will
  be aggregated, BIT_DMA_AGG_TO_V1 configures a timeout for aggregation
  and BIT_EN_PRE_CALC makes the chip honor the limits more effectively)

Use multiple consecutive reads in rtw_sdio_read_port() to limit the
number of bytes which are copied by the host from the card in one
MMC/SDIO transfer. This allows receiving a buffer that's larger than
the hosts max_req_size (number of bytes which can be transferred in
one MMC/SDIO transfer). As a result of this the skb_over_panic error
is gone as the rtw88 driver is now able to receive more than 1536 bytes
from the card (either because the incoming packet is larger than that
or because multiple packets have been aggregated).

Fixes: 65371a3f14e7 ("wifi: rtw88: sdio: Add HCI implementation for SDIO based chipsets")
Reported-by: Lukas F. Hartmann <lukas@xxxxxxxxx>
Closes: https://lore.kernel.org/linux-wireless/CAFBinCBaXtebixKbjkWKW_WXc5k=NdGNaGUjVE8NCPNxOhsb2g@xxxxxxxxxxxxxx/
Suggested-by: Ping-Ke Shih <pkshih@xxxxxxxxxxx>
Signed-off-by: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx>
---
 drivers/net/wireless/realtek/rtw88/sdio.c | 24 +++++++++++++++++------
 1 file changed, 18 insertions(+), 6 deletions(-)

diff --git a/drivers/net/wireless/realtek/rtw88/sdio.c b/drivers/net/wireless/realtek/rtw88/sdio.c
index 2c1fb2dabd40..b19262ec5d8c 100644
--- a/drivers/net/wireless/realtek/rtw88/sdio.c
+++ b/drivers/net/wireless/realtek/rtw88/sdio.c
@@ -500,19 +500,31 @@ static u32 rtw_sdio_get_tx_addr(struct rtw_dev *rtwdev, size_t size,
 static int rtw_sdio_read_port(struct rtw_dev *rtwdev, u8 *buf, size_t count)
 {
 	struct rtw_sdio *rtwsdio = (struct rtw_sdio *)rtwdev->priv;
+	struct mmc_host *host = rtwsdio->sdio_func->card->host;
 	bool bus_claim = rtw_sdio_bus_claim_needed(rtwsdio);
 	u32 rxaddr = rtwsdio->rx_addr++;
+	size_t bytes;
 	int ret;
 
 	if (bus_claim)
 		sdio_claim_host(rtwsdio->sdio_func);
 
-	ret = sdio_memcpy_fromio(rtwsdio->sdio_func, buf,
-				 RTW_SDIO_ADDR_RX_RX0FF_GEN(rxaddr), count);
-	if (ret)
-		rtw_warn(rtwdev,
-			 "Failed to read %zu byte(s) from SDIO port 0x%08x",
-			 count, rxaddr);
+	while (count > 0) {
+		bytes = min_t(size_t, host->max_req_size, count);
+
+		ret = sdio_memcpy_fromio(rtwsdio->sdio_func, buf,
+					 RTW_SDIO_ADDR_RX_RX0FF_GEN(rxaddr),
+					 bytes);
+		if (ret) {
+			rtw_warn(rtwdev,
+				 "Failed to read %zu byte(s) from SDIO port 0x%08x",
+				 bytes, rxaddr);
+			break;
+		}
+
+		count -= bytes;
+		buf += bytes;
+	}
 
 	if (bus_claim)
 		sdio_release_host(rtwsdio->sdio_func);
-- 
2.41.0