On 14/04/2020 20:16, Clément Péron wrote:
Hi Mark,
On Tue, 14 Apr 2020 at 20:55, Mark Brown <broonie@xxxxxxxxxx> wrote:
On Tue, Apr 14, 2020 at 08:20:23PM +0200, Clément Péron wrote:
Hi Liam and Mark,
You might want to flag stuff like this in the subject line, I very
nearly deleted this without opening it since most of the email I get
about panfrost appears to be coming from me having sent patches rather
than being relevant.
Ok will do next time,
We are having an issue with Panfrost driver registering two times the
same regulator and giving an error when trying to create the debugfs
folder.
Could you clarify if it is allowed for a device to register two times
the same regulator?
I check Documentation/power/regulator/regulator.rst but this point is
not specified.
We don't actively prevent it and I can't think what other than debugfs
might run into problems (and that's just a warning) but it does seem
like a weird thing to want to do and like it's pointing to some
confusion in your code with two different parts of the device
controlling the same supply independently. What's the use case here?
Panfrost first probe clock, reset and regulator in device_init:
https://elixir.bootlin.com/linux/v5.7-rc1/source/drivers/gpu/drm/panfrost/panfrost_drv.c#L602
Then it probe for optional devfreq, devfreq will get opp tables and
also get regulator again.
https://elixir.bootlin.com/linux/v5.7-rc1/source/drivers/gpu/drm/panfrost/panfrost_drv.c#L609
That's can be reworked and Panfrost can only probe regulator if there
is no opp-table.
This is what I was thinking about looking at. But it may make sense
instead to extend the regulator API to allow multiple regualtor_get()
calls for a single device. I haven't had time to dig into how difficult
this would be.
But if multiple regulator is not an issue and as each request is logic.
The first in device_init assure to enable the regulator and the second
in OPP assure the voltage level.
Maybe we can just fix this warning?
From what I can see in the code, just silencing the warning would lead
to 'odd' behaviour with debugfs. The first struct regulator Panfrost
acquires is the one that is used purely for turning the GPU on (no
voltage scaling). The second struct regulator is the one which is
obtained by the OPP framework. However the debugfs entries point into
the actual struct regulator, so it would be far more logical/useful if
those were pointing into the second struct regulator.
Ideally calling regulator_get a second time for the same device would
simply return the same struct regulator object (with a reference count
increment).
Perhaps a better approach would be for Panfrost to hand over the struct
regulator objects it has already got to the OPP framework. I.e. open
code dev_pm_opp_set_regulators(), but instead of calling
regulator_get_optional() simply populate the regulators we already have?
The other benefit of that is it would provide a clear hand-over of
responsibility between Panfrost handling it's own regulators and the OPP
framework picking up the work. The disadvantage is that Panfrost would
have to track whether the regulators have been handed over or not.
Steve
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