[Freedreno] [[DPU]PATCH] drm/msm/dsi: move the API setting PLL src to modeset_init()

[Doug Anderson]

Hi,

On Tue, Jun 26, 2018 at 10:27 AM, Rob Clark <robdclark at gmail.com> wrote:
> On Tue, Jun 26, 2018 at 11:55 AM, Doug Anderson <dianders at chromium.org> wrote:
>> Hi,
>>
>> On Mon, Jun 25, 2018 at 9:45 PM, Sandeep Panda <spanda at codeaurora.org> wrote:
>>> From: Abhinav Kumar <abhinavk at codeaurora.org>
>>>
>>> Setting the DSI PLL src in probe doesn't provide the clock
>>> driver sufficient time to reclaim unused clock resources
>>> from coreboot resulting in warnings from clock driver.
>>>
>>> Move the DSI PLL src setting to modeset_init() so that the
>>> clock driver can claim unused display clock resources before
>>> the display driver requests for them again.
>>
>> IMHO this is a bad design.  Sean and Stephen can feel free to override
>> me, but I think the clock driver should be improved to handle this
>> case and not require the clock to get disabled before Linux enables
>> it.
>>
>
> I experimented with it a while back[1] (in this case w/ lk lighting up
> the display).  In that case I needed both the clk and gdsc code to
> realize that clks/gdsc's were on at boot, and fixup the refcnt of the
> clks (and parent clocks and so on).  And then when probed the display
> driver would check if clocks were enabled to decide to readback the
> state from the hw.  (Maybe you can short-circuit some of that if you
> only care about DSI panels with a single fixed resolution, but as soon
> as external displays come into the picture you can't assume so much
> about the hw  state.)
>
> BR,
> -R
>
> [1] https://github.com/freedreno/kernel-msm/commits/display-handover

It seems like something like that is the right real solution here, but
I guess someone needs to step up and work on it.

...in general I'm wary of any patch that will not work when
"clk_ignore_unused" is passed as a command line parameter.  It's
useful to be able to use this command line parameter for debugging
sometimes and it would be unfortunate if doing so spewed a bunch of
extra warnings.


On a side node, it appears that even without ${SUBJECT} patch the
warnings seem to have gone away with the latest stack of patches I've
been testing.  The warnings don't even come back with
"clk_ignore_unused".  I haven't personally dug into why, but I figured
I'd mention it.


-Doug