linux-kernel - Re: [PATCH 1/3] ALSA: hda/tegra: Skip reset on BPMP devices

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Date:   Tue, 7 Dec 2021 20:19:10 +0530
From:   Sameer Pujar <spujar@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>, tiwai@...e.com,
        broonie@...nel.org, lgirdwood@...il.com, robh+dt@...nel.org,
        thierry.reding@...il.com, perex@...ex.cz
Cc:     jonathanh@...dia.com, alsa-devel@...a-project.org,
        devicetree@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-kernel@...r.kernel.org, stable@...r.kernel.org,
        Mohan Kumar <mkumard@...dia.com>
Subject: Re: [PATCH 1/3] ALSA: hda/tegra: Skip reset on BPMP devices



On 12/7/2021 7:37 PM, Dmitry Osipenko wrote:
> 07.12.2021 15:40, Sameer Pujar пишет:
>>
>> On 12/7/2021 5:35 PM, Dmitry Osipenko wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> 07.12.2021 15:00, Sameer Pujar пишет:
>>>> On 12/7/2021 3:52 PM, Dmitry Osipenko wrote:
>>>>> 07.12.2021 09:32, Sameer Pujar пишет:
>>>>>> HDA regression is recently reported on Tegra194 based platforms.
>>>>>> This happens because "hda2codec_2x" reset does not really exist
>>>>>> in Tegra194 and it causes probe failure. All the HDA based audio
>>>>>> tests fail at the moment. This underlying issue is exposed by
>>>>>> commit c045ceb5a145 ("reset: tegra-bpmp: Handle errors in BPMP
>>>>>> response") which now checks return code of BPMP command response.
>>>>>>
>>>>>> The failure can be fixed by avoiding above reset in the driver,
>>>>>> but the explicit reset is not necessary for Tegra devices which
>>>>>> depend on BPMP. On such devices, BPMP ensures reset application
>>>>>> during unpowergate calls. Hence skip reset on these devices
>>>>>> which is applicable for Tegra186 and later.
>>>>> The power domain is shared with the display, AFAICS. The point of reset
>>>>> is to bring h/w into predictable state. It doesn't make sense to me to
>>>>> skip the reset.
>>>> Yes the power-domain is shared with display. As mentioned above,
>>>> explicit reset in driver is not really necessary since BPMP is already
>>>> doing it during unpowergate stage. So the h/w is already ensured to be
>>>> in a good state.
>>> If you'll reload the driver module, then h/w won't be reset.
>> How the reload case would be different? Can you please specify more
>> details if you are referring to a particular scenario?
> You have a shared power domain. Since power domain can be turned off
> only when nobody keeps domain turned on, you now making reset of HDA
> controller dependent on the state of display driver.

I don't think that the state of display driver would affect. The HDA 
driver itself can issue unpowergate calls which in turn ensures h/w 
reset. If display driver is already runtime active, HDA driver runtime 
resume after this would be still fine since h/w reset is already applied 
during display runtime resume. Note that both HDA and display resets are 
connected to this power-domain and BPMP applies these resets during 
unpowergate.

> Do you want to have
> inconsistent h/w reset behaviour depending on the runtime state of
> display driver?

Of course no.