Re: [PATCH] drm: Call sysfs_notify after changing drm_connector::dpms

[Karsten Wiese <fzuuzf@xxxxxxxxxxxxxx>]

2017-09-27 9:18 GMT+02:00 Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>:

On Wed, 27 Sep 2017, Karsten Wiese <fzuuzf@xxxxxxxxxxxxxx> wrote:
> 2017-09-25 15:48 GMT+02:00 Jani Nikula <jani.nikula@xxxxxxxxxxxxxxx>:
>
>> On Tue, 19 Sep 2017, Karsten Wiese <fzuuzf@xxxxxxxxxxxxxx> wrote:
>> > This makes poll work for the
>> > /sys/class/drm/cardX/connectorY/dpms attributes.
>>
>> I guess the question is, what are you trying to achieve? What is the
>> problem that this solves?
>>
> ​
> The patch enables cpu cycle less waiting for dpms flag changes.
>
> Here it lets a screen brightness ​setting daemon know which monitor to
> handle.  One of the attached screens gets confused if it is set just
> after being switched on, hence the daemon leaves it untouched until it
> has been active for some seconds.

Screen brightness settings daemon?

Running on a laptop lacking an ambient light sensor employing it's webcam instead to measure ambient light and adjust monitors' brightnesses accordingly.

What exactly do you mean by "if it is
set"? What interface are you using to change brightness?

The external monitor's brightness is adjusted by DDC/CI via the /dev/i2c-x the monitor is attached to.

 I there a saner interface to use?

What happens
when the display "gets confused"?

The monitor wrongly toggles sharpness if it receives the brightness adjusting​

​ DDC/CI soon after resuming from power saving state.

My first instinct is that you're proposing a new kernel ABI to solve an
issue you shouldn't be solving in userspace to begin with.

Calculating ambient light from pictures acquired via ​

​v4l​2 in kernel seamed wrong to me.

Or that
perhaps the userspace should be doing this in cooperation with the drm
master, not standalone.

Is there a way to call into the drm-master (xscreensaver/xserver​ here​

​) ​with the call only returning if a monitor's power state changed?

There is DPMSInfo, but it returns immediately rendering the daemon less efficient.

BR,

Karsten

BR,
Jani.

>
> Without the p​atch the daemon would have to actively read the dpms flag
> every once in a while.
>
>
>>
>> We have zero sysfs_notify in all of drm AFAICT.
>
>
> Yes I noticed too and looked for some dbus signal to listen to​ but didn't
> find any.
>
> BR,
> Karsten
>
>>
>> BR,
>> Jani.
>>
>>
>> >
>> > Tested with i915 suspended by XScreenServer and
>> > suspend to RAM.
>> >
>> > Signed-off-by: Karsten Wiese <fzuuzf@xxxxxxxxxxxxxx>
>> > ---
>> >  drivers/gpu/drm/drm_atomic.c        | 4 ++++
>> >  drivers/gpu/drm/drm_atomic_helper.c | 6 +++++-
>> >  2 files changed, 9 insertions(+), 1 deletion(-)
>> >
>> > diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
>> > index 2fd383d..b6fa87b 100644
>> > --- a/drivers/gpu/drm/drm_atomic.c
>> > +++ b/drivers/gpu/drm/drm_atomic.c
>> > @@ -1880,6 +1880,10 @@ int drm_atomic_connector_commit_dpms(struct
>> drm_atomic_state *state,
>> >  out:
>> >       if (ret != 0)
>> >               connector->dpms = old_mode;
>> > +     else
>> > +             if (connector->dpms != old_mode)
>> > +                     sysfs_notify(&connector->kdev->kobj, NULL,
>> "dpms");
>> > +
>> >       return ret;
>> >  }
>> >
>> > diff --git a/drivers/gpu/drm/drm_atomic_helper.c
>> b/drivers/gpu/drm/drm_atomic_helper.c
>> > index 4e53aae..6198772 100644
>> > --- a/drivers/gpu/drm/drm_atomic_helper.c
>> > +++ b/drivers/gpu/drm/drm_atomic_helper.c
>> > @@ -921,12 +921,16 @@ drm_atomic_helper_update_legacy_modeset_state(struct
>> drm_device *dev,
>> >               crtc = new_conn_state->crtc;
>> >               if ((!crtc && old_conn_state->crtc) ||
>> >                   (crtc && drm_atomic_crtc_needs_modeset(crtc->state)))
>> {
>> > -                     int mode = DRM_MODE_DPMS_OFF;
>> > +                     int old_mode, mode = DRM_MODE_DPMS_OFF;
>> >
>> >                       if (crtc && crtc->state->active)
>> >                               mode = DRM_MODE_DPMS_ON;
>> >
>> > +                     old_mode = connector->dpms;
>> >                       connector->dpms = mode;
>> > +                     if (old_mode != mode)
>> > +                             sysfs_notify(&connector->kdev->kobj,
>> > +                                             NULL, "dpms");
>> >               }
>> >       }
>>
>> --
>> Jani Nikula, Intel Open Source Technology Center
>>

--
Jani Nikula, Intel Open Source Technology Center

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