linux-kernel - Re: [PATCH] ASoC: fsl: imx-pcm-dma: Don't request dma channel in probe

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Message-ID: <20210421174629.GD4617@sirena.org.uk>
Date:   Wed, 21 Apr 2021 18:46:29 +0100
From:   Mark Brown <broonie@...nel.org>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     Robin Gong <yibin.gong@....com>,
        Shengjiu Wang <shengjiu.wang@...il.com>,
        Nicolin Chen <nicoleotsuka@...il.com>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        Timur Tabi <timur@...nel.org>, Xiubo Li <Xiubo.Lee@...il.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "S.j. Wang" <shengjiu.wang@....com>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Takashi Iwai <tiwai@...e.com>,
        "linaro-mm-sig@...ts.linaro.org" <linaro-mm-sig@...ts.linaro.org>,
        dl-linux-imx <linux-imx@....com>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        Fabio Estevam <festevam@...il.com>,
        "perex@...ex.cz" <perex@...ex.cz>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "sumit.semwal@...aro.org" <sumit.semwal@...aro.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-media@...r.kernel.org" <linux-media@...r.kernel.org>
Subject: Re: [PATCH] ASoC: fsl: imx-pcm-dma: Don't request dma channel in
 probe

On Wed, Apr 21, 2021 at 07:43:18PM +0200, Lucas Stach wrote:

> If your driver code drops the rpm refcount to 0 and starts the
> autosuspend timer while a cyclic transfer is still in flight this is
> clearly a bug. Autosuspend is not there to paper over driver bugs, but
> to amortize cost of actually suspending and resuming the hardware. Your
> driver code must still work even if the timeout is 0, i.e. the hardware
> is immediately suspended after you drop the rpm refcount to 0.

> If you still have transfers queued/in-flight the driver code must keep
> a rpm reference.

Right, failing to do that is a clear bug.

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