[nexus7-flo] backlight brightness

[Thierry Reding]

On Fri, Apr 29, 2016 at 08:04:09AM -0400, Rob Clark wrote:
> On Fri, Apr 29, 2016 at 1:32 AM, Vinay Simha <simhavcs at gmail.com> wrote:
> > hi,
> >
> > In nx7, backlight brightness control is controlled by dcs commands of
> > MIPI_DCS_SET_DISPLAY_BRIGHTNESS.
> > there is no PWM going to panel interface directly as we have in ifc6410/nx5
> 
> afaiu it is not uncommon to need to control backlight via panel (ie, I
> think basically all adaptive-backlight panels).  I think the answer is
> for these panels, the panel driver would register it's own backlight
> driver, rather than get a (pwm, etc) backlight via dt bindings.

Yes, that'd be my recommendation as well.

> Possibly if the backlight commands are standardized enough then we
> could implement a single drm_panel_dsi_backlight helper which could be
> created by any of the dsi adaptive-backlight panels (ie. pass in a
> 'struct mipi_dsi_device *').. something like:
> 
> struct drm_panel_dsi_backlight {
>     struct mipi_panel_dsi_device *link;
>     ...
> }
> 
> struct backlight_device *drm_panel_create_dsi_backlight(struct
> mipi_panel_dsi_device *link)
> {
>     struct drm_panel_dsi_backlight *dsi_bl;
>     ...
>     return devm_backlight_device_register(&link->dev, ..., dsi_bl,
> dsi_bl_ops, props);
> }

I agree it would make sense to have a DCS specific helper for backlight.
I'm somewhat sceptical about the standardization, even though these seem
to be part of DCS 1.3. But perhaps we can start by being optimistic.

Thierry
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