linux-kernel - Re: [PATCH] ASoC: fsl_esai: fix the channel swap issue after xrun

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Message-ID: <20190523101055.GA28470@Asurada-Nvidia.nvidia.com>
Date:   Thu, 23 May 2019 03:10:56 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     "broonie@...nel.org" <broonie@...nel.org>,
        "S.j. Wang" <shengjiu.wang@....com>
Cc:     "timur@...nel.org" <timur@...nel.org>,
        "Xiubo.Lee@...il.com" <Xiubo.Lee@...il.com>,
        "festevam@...il.com" <festevam@...il.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ASoC: fsl_esai: fix the channel swap issue after xrun

Hello Shengjiu,

On Thu, May 23, 2019 at 09:53:42AM +0000, S.j. Wang wrote:
> > > +     /*
> > > +      * Add fifo reset here, because the regcache_sync will
> > > +      * write one more data to ETDR.
> > > +      * Which will cause channel shift.
> > 
> > Sounds like a bug to me...should fix it first by marking the data registers as
> > volatile.
> > 
> The ETDR is a writable register, it is not volatile. Even we change it to
> Volatile, I don't think we can't avoid this issue. for the regcache_sync
> Just to write this register, it is correct behavior.

Is that so? Quoting the comments of regcache_sync():
"* regcache_sync - Sync the register cache with the hardware.
 *
 * @map: map to configure.
 *
 * Any registers that should not be synced should be marked as
 * volatile."

If regcache_sync() does sync volatile registers too as you said,
I don't mind having this FIFO reset WAR for now, though I think
this mismatch between the comments and the actual behavior then
should get people's attention.

Thank you