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

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Date:   Tue, 15 Oct 2019 16:45:43 +0300
From:   Adrian Hunter <adrian.hunter@...el.com>
To:     Faiz Abbas <faiz_abbas@...com>, linux-kernel@...r.kernel.org,
        linux-mmc@...r.kernel.org
Cc:     ulf.hansson@...aro.org, asutoshd@...eaurora.org,
        riteshh@...eaurora.org, venkatg@...eaurora.org
Subject: Re: [RFC] mmc: cqhci: commit descriptors before setting the doorbell

On 15/10/19 10:55 AM, Faiz Abbas wrote:
> 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@...com>
>> ---
>>
>> 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?

Perhaps we could do both changes i.e. add wmb() and convert to non-relaxed
readl/writel