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

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Message-ID: <08b6a1f7-3c4d-ce6a-0d00-450f7bd4eeb3@nvidia.com>
Date:   Thu, 30 Jan 2020 18:58:37 +0000
From:   Jon Hunter <jonathanh@...dia.com>
To:     Dmitry Osipenko <digetx@...il.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


On 30/01/2020 18:26, Dmitry Osipenko wrote:
> 30.01.2020 21:06, Dmitry Osipenko пишет:
>> 30.01.2020 19:08, Dmitry Osipenko пишет:
>>> 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.
>>
>> I started to look at it and found that the .device_pause() hook isn't
>> implemented by the driver. So, it's fine to remove the context's
>> save-restore for now.
>>
>> Jon, what about to keep this patch as-is? Later on I'll take a look at
>> implementing the proper pausing functionality and try to cleanup code a
>> bit further (remove the free list usage, etc).
> 
> Ah, only T114+ supports the per-channel pausing. So, I won't care about
> implementing the device_pause(), let's leave it to somebody else :)

That's fine. We have lived with out it for this long.

Jon

-- 
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