Re: [PATCH 0/2] mmc: sdhci: add quirk to disable bounce buffer

[Linus Walleij]

On Fri, Oct 24, 2025 at 7:37 AM Adrian Hunter <adrian.hunter@xxxxxxxxx> wrote:

> > These patches were mildly revealing, I see this near the start of the logs:
> > [   32.222988] b43-sdio mmc1:0001:1: Chip ID 14e4:4318

B43 WLAN eh? That driver is heavily bitrotted.

Anyways b43 does:

#define B43_SDIO_BLOCK_SIZE    64    /* rx fifo max size in bytes */

sdio_set_block_size(func, B43_SDIO_BLOCK_SIZE);

So that is an indication it does not want anything bigger than
that in it's FIFO.

It does this by setting blksize down to 64 and then sending
(probably) a train of sg_list:ed requests that the bound buffer
will merge into a contiguous request much bigger than 64
bytes to speed things up.

But I don't think the bounce buffer has proper SDIO minimum
block size awareness. It should simply step out of the way when
we do SDIO.

I will send a patch you can test.

Yours,
Linus Walleij