[PATCH] net: rswitch: Add missing cache invalidate of TX descriptor

[Enric Balletbo i Serra]

Hi,

Thanks Marek for fixing this.

On Thu, Dec 19, 2024 at 12:02 PM Marek Vasut
<marek.vasut+renesas at mailbox.org> wrote:
>
> TFTP transfers of large files, for example 128 MiB, can sporadically
> get stuck and the transfer slows down considerably.
>
> This happens because the TX DMA descriptor in DRAM becomes out of sync
> with the view of the TX DMA descriptor content from the CPU side, which
> is viewed through the CPU caches. In order to guarantee these two views
> are consistent, the cache over TX DMA descriptor that has possibly been
> written by the rswitch hardware must first be invalidated, only then can
> the descriptor be cleared and updated by the CPU, and finally the cache
> over that area must be flushed back into DRAM to make sure the rswitch
> hardware has consistent view of the updated descriptor content.
>
> The very first invalidation operation was missing, which led to sporadic
> corruption of the TX DMA descriptor. Fix it, add the missing invalidation
> operation.
>
> Reported-by: Enric Balletbo i Serra <eballetb at redhat.com>
> Signed-off-by: Marek Vasut <marek.vasut+renesas at mailbox.org>

I did a stress test with one S4 Spider board tftp'ing a big image for
more than 1 hour without getting stuck, before this patch this test
didn't succeed, so

Tested-by: Enric Balletbo i Serra <eballetb at redhat.com>

> ---
> Cc: Joe Hershberger <joe.hershberger at ni.com>
> Cc: Nobuhiro Iwamatsu <iwamatsu at nigauri.org>
> Cc: Ramon Fried <rfried.dev at gmail.com>
> Cc: Tom Rini <trini at konsulko.com>
> Cc: u-boot at lists.denx.de
> ---
>  drivers/net/rswitch.c | 1 +
>  1 file changed, 1 insertion(+)
>
> diff --git a/drivers/net/rswitch.c b/drivers/net/rswitch.c
> index 91e2c7b7845..259d584ac98 100644
> --- a/drivers/net/rswitch.c
> +++ b/drivers/net/rswitch.c
> @@ -836,6 +836,7 @@ static int rswitch_send(struct udevice *dev, void *packet, int len)
>
>         /* Update TX descriptor */
>         rswitch_flush_dcache((uintptr_t)packet, len);
> +       rswitch_invalidate_dcache((uintptr_t)desc, sizeof(*desc));
>         memset(desc, 0x0, sizeof(*desc));
>         desc->die_dt = DT_FSINGLE;
>         desc->info_ds = len;
> --
> 2.45.2
>