Re: [PATCH] drm/i915: Backlight Control over AUX feature

Daniel Vetter
2015-09-14T13:13:08Z

On Mon, Sep 14, 2015 at 01:00:26PM +0300, Jani Nikula wrote:
> On Thu, 10 Sep 2015, Yetunde Adebisi <yetundex.adebisi@intel.com> wrote:
> > This patch adds support for Backlight Control over the AUX channel for
> > DP and eDP connectors. It allows the backlight of DP and eDP connected
> > displays to be controlled from software using sysfs interface.
>
> Which spec says there's DPCD backlight control support on non-embedded
> Display Port? AFAICT it's just eDP.
>
> > The code first checks if the DP/eDP display has the capability for
> > backlight control by reading Display Control DPCD registers as defined
> > by the eDP v1.3 VESA specs.
> > It then registers a /sys/backlight device if backlight control is
> > supported.
> >
> > It provides functions to
> > - Register a sysfs backlight interface if the eDP/DP connnector is
> > capable of aux backlight control
> > - Read the current backlight level from DPCD register 0x722
> > - Change the backlight level
> > - Disable/Enable the backlight by writing to DPCD register 0x720
>
> IMO the design should be to move dev_priv->display backlight hooks to be
> connector specific, in intel_panel, and it would be transparent whether
> backlight control is AUX based, GPU PWM based, PMIC PWM based, or DSI
> command mode based. I've given the exact same feedback about the recent
> DSI command mode backlight code.

Registering piles of backlight controllers and letting userspace pick it
is how it works currently. Ugly, but well that's how it is. Fixing that up
would be a bit of work ...
-Daniel
--
Daniel Vetter
Software Engineer, Intel Corporation