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

[Ping-Ke Shih]

> -----Original Message-----
> From: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx>
> Sent: Monday, July 10, 2023 3:57 AM
> To: linux-wireless@xxxxxxxxxxxxxxx
> Cc: linux-kernel@xxxxxxxxxxxxxxx; jernej.skrabec@xxxxxxxxx; Ping-Ke Shih <pkshih@xxxxxxxxxxx>;
> ulf.hansson@xxxxxxxxxx; kvalo@xxxxxxxxxx; tony0620emma@xxxxxxxxx; Martin Blumenstingl
> <martin.blumenstingl@xxxxxxxxxxxxxx>; Lukas F . Hartmann <lukas@xxxxxxxxx>
> Subject: [PATCH] wifi: rtw88: sdio: Honor the host max_req_size in the RX path
> 
> 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).

I assume your conclusion is correct for all platforms, so I add my reviewed-by.
But, I think it would be better that Lukas can help to test this patch on his
platform, and give a tested-by tag before getting this patch merged. 

> 
> 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@mail.gmail.
> com/
> Suggested-by: Ping-Ke Shih <pkshih@xxxxxxxxxxx>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx>

Reviewed-by: Ping-Ke Shih <pkshih@xxxxxxxxxxx>

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