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

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Message-ID: <fac9ad28-dbc3-3948-d99c-742420f3e651@ti.com>
Date:   Tue, 15 Oct 2019 13:25:15 +0530
From:   Faiz Abbas <faiz_abbas@...com>
To:     <linux-kernel@...r.kernel.org>, <linux-mmc@...r.kernel.org>
CC:     <ulf.hansson@...aro.org>, <asutoshd@...eaurora.org>,
        <riteshh@...eaurora.org>, <adrian.hunter@...el.com>,
        <venkatg@...eaurora.org>
Subject: Re: [RFC] mmc: cqhci: commit descriptors before setting the doorbell

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?

Thanks,
Faiz