[PATCH v2 3/5] media: mediatek: vcodec: Read HW active status from clock

[AngeloGioacchino Del Regno]

Il 15/06/23 02:40, Stephen Boyd ha scritto:
> Quoting AngeloGioacchino Del Regno (2023-06-14 01:13:43)
>> Il 12/06/23 21:19, Stephen Boyd ha scritto:
>>> Quoting AngeloGioacchino Del Regno (2023-06-09 00:42:13)
>>>> Il 09/06/23 01:56, Stephen Boyd ha scritto:
>>>>> Quoting AngeloGioacchino Del Regno (2023-06-08 02:01:58)
>>>>>> Il 08/06/23 10:12, Chen-Yu Tsai ha scritto:
>>>>>>> On Thu, Jun 8, 2023 at 4:57 AM Nícolas F. R. A. Prado
>>>>>>> <nfraprado at collabora.com> wrote:
>>>>
>>>> The firmware gives an indication of "boot done", but that's for the "core" part
>>>> of the vcodec... then it manages this clock internally to enable/disable the
>>>> "compute" IP of the decoder.
>>>>
>>>> As far as I know (and I've been researching about this) the firmware will not
>>>> give any "decoder powered, clocked - ready to get data" indication, and the
>>>> only way that we have to judge whether it is in this specific state or not is
>>>> to check if the "VDEC_ACTIVE" clock got enabled by the firmware.
>>>
>>> Is Linux ever going to use clk consumer APIs like clk_enable/clk_disable
>>> on this VDEC_ACTIVE clk? If the answer is no, then there isn't any
>>> reason to put it in the clk framework, and probably syscon is the way to
>>> go for now.
>>>
>>
>> Not for the current platform, but that may change in future SoCs... we're not sure.
> 
> If you're not using the clk consumer APIs then it shouldn't be a clk.
> 
>>
>>> Another approach could be to wait for some amount of time after telling
>>> firmware to power up and assume the hardware is active.
>>>
>>
>> That would be highly error prone though. Expecting that the HW is alive means that
>> we're 100% sure that both firmware and driver are doing the right thing at every
>> moment, which is something that we'd like to assume but, realistically, for safety
>> reasons we just don't.
>>
>> Should we anyway go for a syscon *now* and then change it to a clock later, if any
>> new platform needs this as a clock?
> 
> Yeah. Or implement this as a power domain and have it read the register
> directly waiting to return from the power_on()?

A power domain would force us to incorrectly describe the hardware in the bindings
though, I think... so, Nícolas, please, let's go for a syscon at this point, as it
really looks like being the only viable option.

Stephen, many thanks for the valuable suggestions and the nice conversation.

Cheers!
Angelo