Re: [PATCH rtw-next v6 3/4] wifi: rtw88: sdio: Fix unhandled RX request interrupt storm

[Luka Gejak]

Hi Alastair,

October 14, 2026 at 9:44 AM, "Alastair D'Silva" <alastair@xxxxxxxxxxx> wrote:

> On 3081-based SDIO chips (e.g. RTL8821CS), hardware does not automatically
> clear REG_SDIO_HISR_RX_REQUEST when the RX buffer is empty. Masking this
> bit out before writing back to HISR prevents it from being acknowledged,
> causing an infinite interrupt storm loop that locks up the system.

In my opinion, I would reword this first sentance. Your own probe shows the
bit does clear, post_drain_hisr comes back as 0x00800030 once the FIFO is
empty, so what the hardware needs is the software acknowledge plus an
empty FIFO. The old code masked the acknowledge out of the writeback so
it never happened, which is the failure the second sentence describes.
As written the first one reads as if the bit could never be cleared and
the drain did not matter. The fix depends on the opposite reading.

Best regards,
Luka Gejak