[Intel-gfx] [PATCH] drm/i915: add psr toggle to debugfs

[Eric Caruso]

On Fri, Mar 13, 2015 at 1:14 PM, Paulo Zanoni <przanoni at gmail.com> wrote:
> 2015-03-13 16:01 GMT-03:00 Daniel Vetter <daniel at ffwll.ch>:
>> On Fri, Mar 13, 2015 at 7:10 PM, Eric Caruso <ejcaruso at chromium.org> wrote:
>>> This patch allows userspace to toggle PSR through a debugfs interface.
>>> It adds functionality to write 0 or 1 to the existing
>>> i915_edp_psr_status file in order to change the relevant module
>>> parameter and enable/disable PSR.
>>>
>>> Previous upstream feedback did not like making it a connector property
>>> or putting it in sysfs because that would require API stability going
>>> forward. debugfs interfaces do not have this restriction.
>>>
>>> Signed-off-by: Eric Caruso <ejcaruso at chromium.org>
>>
>> What do we need this for? debugfs is generally for debugging (where
>> the module option should be enough) and for testcases (which doesn't
>> seem to be the case here).
>
> What is wrong with "echo 1 > /sys/module/i915/parameters/enable_psr"?
>
>> -Daniel
>> --
>> Daniel Vetter
>> Software Engineer, Intel Corporation
>> +41 (0) 79 365 57 48 - http://blog.ffwll.ch
>> _______________________________________________
>> Intel-gfx mailing list
>> Intel-gfx at lists.freedesktop.org
>> http://lists.freedesktop.org/mailman/listinfo/intel-gfx
>
>
>
> --
> Paulo Zanoni

Forgive me if this is wrong, but updating the module parameter doesn't
change whether or not PSR is enabled immediately. You need to go through
intel_enable_ddi for this to take effect.

We were using something like this for testing on Chromium OS, because
PSR would sometimes cause issues. This allows us to change the module
parameter and enable/disable PSR in one step.

The upstream feedback I mentioned was done about a year ago:
http://lists.freedesktop.org/archives/intel-gfx/2014-March/041896.html
It seemed to favor a debugfs knob for this.