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

[Faiz Abbas]

Hi,

On 15/10/19 12:08 AM, Faiz Abbas 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>
> ---
> 
> 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")

So I see that cqhci_readl/writel() use readl/writel_relaxed() which
seems to be causing this issue. Should I just fix this by converting
those to readl/writel with memory barriers instead?

Thanks,
Faiz