Re: [RFC] mmc: cqhci: commit descriptors before setting the doorbell

[Ulf Hansson]

On Mon, 14 Oct 2019 at 20:37, Faiz Abbas <faiz_abbas@xxxxxx> wrote:
>
> Add a write memory barrier to make sure that descriptors are actually
> written to memory before ringing the doorbell.
>
> Signed-off-by: Faiz Abbas <faiz_abbas@xxxxxx>

Applied for fixes and by adding a stable tag, thanks!

BTW, do you have a valid commit that it fixes?

Kind regards
Uffe


> ---
>
> This patch fixes a very infrequent ADMA error (1 out of 100 times) that
> I have been seeing after enabling command queuing for J721e.
> Also looking at memory-barriers.txt and this commit[1],
> it looks like we should be doing this before any descriptor write
> followed by a doorbell ring operation. It'll be nice if someone with more
> expertise in memory barriers can comment.
>
> [1] ad1a1b9cd67a ("scsi: ufs: commit descriptors before setting the
>     doorbell")
>
>  drivers/mmc/host/cqhci.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/mmc/host/cqhci.c b/drivers/mmc/host/cqhci.c
> index f7bdae5354c3..5047f7343ffc 100644
> --- a/drivers/mmc/host/cqhci.c
> +++ b/drivers/mmc/host/cqhci.c
> @@ -611,7 +611,8 @@ static int cqhci_request(struct mmc_host *mmc, struct mmc_request *mrq)
>         cq_host->slot[tag].flags = 0;
>
>         cq_host->qcnt += 1;
> -
> +       /* Make sure descriptors are ready before ringing the doorbell */
> +       wmb();
>         cqhci_writel(cq_host, 1 << tag, CQHCI_TDBR);
>         if (!(cqhci_readl(cq_host, CQHCI_TDBR) & (1 << tag)))
>                 pr_debug("%s: cqhci: doorbell not set for tag %d\n",
> --
> 2.19.2
>