linux-kernel - Re: [PATCH 1/2] ASoC: AMD: Fix simultaneous playback and capture on different channel

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Date:   Mon, 10 Sep 2018 12:38:20 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Akshu Agrawal <akshu.agrawal@....com>
Cc:     djkurtz@...omium.org, Alexander.Deucher@....com,
        Liam Girdwood <lgirdwood@...il.com>,
        Jaroslav Kysela <perex@...ex.cz>,
        Takashi Iwai <tiwai@...e.com>,
        "Mukunda, Vijendar" <Vijendar.Mukunda@....com>,
        Kuninori Morimoto <kuninori.morimoto.gx@...esas.com>,
        Wei Yongjun <weiyongjun1@...wei.com>,
        "moderated list:SOUND - SOC LAYER / DYNAMIC AUDIO POWER MANAGEM..." 
        <alsa-devel@...a-project.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 1/2] ASoC: AMD: Fix simultaneous playback and capture on
 different channel

On Mon, Sep 10, 2018 at 01:36:29PM +0530, Akshu Agrawal wrote:
> If capture and playback are started on different channel (I2S/BT)
> there is a possibilty that channel information passed from machine driver
> is overwritten before the configuration is done in dma driver.
> Example:
> 113.597588: cz_max_startup: ---playback sets BT channel
> 113.597694: cz_dmic1_startup: ---capture sets I2S channel
> 113.597979: acp_dma_hw_params: ---configures capture for I2S channel
> 113.598114: acp_dma_hw_params: ---configures playback for I2S channel
> 
> This is fixed by having lock between startup and prepare. This ensures
> no other codec startup gets called between a codec's startup(where channel
> info is set) and hw_params(where channel info is read).

This isn't viable - the driver will deadlock if the application hits an
error and never gets to startup, or if the application tries to
simultaneously configure two channels (ie, do all the prepares and then
all the parameter configuration and then startup).  The DMA driver needs
to remember the configurations for the different channels separately.

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