wifi: rtw88: sdio: Honor the host max_req_size in the RX path

In the Linux kernel, the following vulnerability has been resolved:

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 works around the

problem for some time (but does not fully fix it). 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() and 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).

In case of an receive errors (-EILSEQ has been observed by Lukas) we

need to drain the remaining data from the card's buffer, otherwise the

card will return corrupt data for the next rtw_sdio_read_port() call.