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

[Daniel Vetter]

On Wed, Sep 27, 2017 at 12:29:46AM +0200, Karsten Wiese wrote:
> 2017-09-25 15:48 GMT+02:00 Jani Nikula <jani.nikula at linux.intel.com>:
> 
> > On Tue, 19 Sep 2017, Karsten Wiese <fzuuzf at googlemail.com> 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.

Without knowing more details, but a brightness deamon in userspace sounds
rather wrong. The driver is supposed to take care of this and shut down
the backlight when we disable the output for a panel.

> Without the p​atch the daemon would have to actively read the dpms flag
> every once in a while.

On top of that, any uabi changes need open source userspace.
-Daniel

> 
> 
> >
> > 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 at googlemail.com>
> > > ---
> > >  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
> >

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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch