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Subject: Re: [PATCH v6 12/16] dmaengine: tegra-apb: Clean up suspend-resume
To:     Dmitry Osipenko <digetx@gmail.com>,
        Laxman Dewangan <ldewangan@nvidia.com>,
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From:   Jon Hunter <jonathanh@nvidia.com>
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Date:   Thu, 30 Jan 2020 18:58:37 +0000
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On 30/01/2020 18:26, Dmitry Osipenko wrote:
> 30.01.2020 21:06, Dmitry Osipenko =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>> 30.01.2020 19:08, Dmitry Osipenko =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>> 30.01.2020 17:09, Jon Hunter =D0=BF=D0=B8=D1=88=D0=B5=D1=82:
>>>>
>>>> On 30/01/2020 04:38, Dmitry Osipenko wrote:
>>>>> It is enough to check whether hardware is busy on suspend and to rese=
t
>>>>> it across of suspend-resume because channel's configuration is fully
>>>>> re-programmed on each DMA transaction anyways and because save-restor=
e
>>>>> 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 ti=
me of
>>>>> suspend, so save-restore is not needed at all).
>>>>
>>>> I guess if we ever wanted to support SNDRV_PCM_INFO_PAUSE for audio an=
d
>>>> support the pause callback, then saving and restoring the channels cou=
ld
>>>> be needed. Right now I believe that it will just terminate_all transfe=
rs
>>>> for audio on entering suspend. Any value in keeping this?
>>>
>>> Indeed, looks like [1] pauses DMA during suspend if SNDRV_PCM_INFO_PAUS=
E
>>> 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).
>=20
> 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

--=20
nvpublic