linux-kernel - Re: [PATCH v6 12/16] dmaengine: tegra-apb: Clean up suspend-resume

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Date:   Thu, 30 Jan 2020 19:08:57 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Jon Hunter <jonathanh@...dia.com>,
        Laxman Dewangan <ldewangan@...dia.com>,
        Vinod Koul <vkoul@...nel.org>,
        Dan Williams <dan.j.williams@...el.com>,
        Thierry Reding <thierry.reding@...il.com>,
        Michał Mirosław <mirq-linux@...e.qmqm.pl>
Cc:     dmaengine@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6 12/16] dmaengine: tegra-apb: Clean up suspend-resume

30.01.2020 17:09, Jon Hunter пишет:
> 
> On 30/01/2020 04:38, Dmitry Osipenko wrote:
>> It is enough to check whether hardware is busy on suspend and to reset
>> it across of suspend-resume because channel's configuration is fully
>> re-programmed on each DMA transaction anyways and because save-restore
>> of an active channel won't end up well without pausing transfer prior to
>> saving of the state (note that all channels shall be idling at the time of
>> suspend, so save-restore is not needed at all).
> 
> I guess if we ever wanted to support SNDRV_PCM_INFO_PAUSE for audio and
> support the pause callback, then saving and restoring the channels could
> be needed. Right now I believe that it will just terminate_all transfers
> for audio on entering suspend. Any value in keeping this?

Indeed, looks like [1] pauses DMA during suspend if SNDRV_PCM_INFO_PAUSE
is supported.

[1]
https://elixir.bootlin.com/linux/v5.5/source/sound/core/pcm_dmaengine.c#L199

So we'll need to save-restore context only if DMA is in a paused state
during suspend, I'll adjust this patch to do that and will see if
enabling SNDRV_PCM_INFO_PAUSE works.