linux-kernel - Re: [alsa-devel] [PATCH] fsl_ssi: set fifo watermark to more reliable value

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Message-ID: <CAOMZO5AS7TPu1PmdNUZuSEJQO2C7L+7Kn2wpetoxHCzwHiyokg@mail.gmail.com>
Date:   Tue, 3 Jan 2017 19:08:53 -0200
From:   Fabio Estevam <festevam@...il.com>
To:     Caleb Crome <ccrome@...il.com>
Cc:     Timur Tabi <timur@...i.org>, Nicolin Chen <nicoleotsuka@...il.com>,
        Xiubo Li <Xiubo.Lee@...il.com>,
        Fabio Estevam <fabio.estevam@....com>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "alsa-devel@...a-project.org" <alsa-devel@...a-project.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Arnaud Mouiche <arnaud.mouiche@...oxia.com>,
        Caleb Crome <caleb@...me.org>
Subject: Re: [alsa-devel] [PATCH] fsl_ssi: set fifo watermark to more reliable value

On Tue, Jan 3, 2017 at 4:22 PM, Caleb Crome <ccrome@...il.com> wrote:
> From: Caleb Crome <caleb@...me.org>
>
> The fsl_ssi fifo watermark is by default set to 2 free spaces (i.e.
> activate DMA on FIFO when only 2 spaces are left.)  This means the
> DMA must service the fifo within 2 audio samples, which is just not
> enough time  for many use cases with high data rate.  In many
> configurations the audio channel slips (causing l/r swap in stereo
> configurations, or channel slipping in multi-channel configurations).
>
> This patch gives more breathing room and allows the SSI to operate
> reliably by changing the fifio refill watermark to 8.
>
> There is no change in behavior for older chips (with an 8-deep fifo).
> Only the newer chips with a 15-deep fifo get the new behavior. I
> suspect a new fifo depth setting could be optimized on the older
> chips too, but I have not tested.
>
> Signed-off-by: Caleb Crome <caleb@...me.org>

Reviewed-by: Fabio Estevam <fabio.estevam@....com>