Re: [PATCH v3 06/14] Documentation: drm/bridge: add document for analogix_dp

[Yakir Yang]

Hi Thierry,

å 2015/8/25 17:12, Thierry Reding åé:
> On Mon, Aug 24, 2015 at 09:48:27AM -0500, Rob Herring wrote:
> > On Mon, Aug 24, 2015 at 7:57 AM, Russell King - ARM Linux
> > <linux@xxxxxxxxxxxxxxxx> wrote:
> > > On Sun, Aug 23, 2015 at 06:23:14PM -0500, Rob Herring wrote:
> > > > On Wed, Aug 19, 2015 at 9:50 AM, Yakir Yang <ykk@xxxxxxxxxxxxxx> wrote:
> > > > > +       -analogix,color-depth:
> > > > > +               number of bits per colour component.
> > > > > +                       COLOR_6 = 0, COLOR_8 = 1, COLOR_10 = 2, COLOR_12 = 3
> > > > This seems pretty generic. Just use 6, 8, 10, or 12 for values. And
> > > > drop the vendor prefix.
> > > Please think about this some more.  What does "color-depth" mean?  Does it
> > > mean the number of bits per colour _component_, or does it mean the total
> > > number of bits to represent a particular colour.  It's confusing as it
> > > stands.
> > Then "component-color-bpp" perhaps?
> There should be no need to have this in DT at all. The BPC is a property
> of the attached panel and it should come from the panel (either the
> panel driver or parsed from EDID if available).

Actually I have send an email about this one to you in version 2, just 
past from that email:

"samsung,color_space" and "samsung,color-depth"

The drm_display_info's color_formats and bpc indicate the monitor 
display ability, but
the edp driver could not take it as input video format directly.

For example, with my DP TV I would found "RGB444 & YCRCB422 & & YCRCB444"
support in drm_display_info.color_formats and 16bit bpc support, but 
RK3288 crtc
driver could only output RGB & ITU formats, so finally 
analogix_dp-rockchip driver
config crtc to RGBaaa 10bpc mode.

In this sutiation, the analogix_dp core driver would pazzled by the 
drm_display_info,
can't chose the right color_space and bpc.

And this is the place that confused me, wish you could give some ideas 
about this one :-)

- Yakir
> > > When we adopted the graph bindings for iMX DRM, I thought exactly at that
> > > time "it would be nice if this could become the standard for binding DRM
> > > components together" but I don't have the authority from either the DT
> > > perspective or the DRM perspective to mandate that.  Neither does anyone
> > > else.  That's the _real_ problem here.
> > >
> > > I've seen several DRM bindings go by which don't use the of-graph stuff,
> > > which means that they'll never be compatible with generic components
> > > which do use the of-graph stuff.
> > It goes beyond bindings IMO. The use of the component framework or not
> > has been at the whim of driver writers as well. It is either used or
> > private APIs are created. I'm using components and my need for it
> > boils down to passing the struct drm_device pointer to the encoder.
> > Other components like panels and bridges have different ways to attach
> > to the DRM driver.
> I certainly support unification, but it needs to be reasonable. There
> are cases where a different structure for the binding work better than
> another and I think this always needs to be evaluated on a case by case
> basis.
>
> Because of that I think it makes sense to make all these framework bits
> opt-in, otherwise we could easily end up in a situation where drivers
> have to be rearchitected (or even DT bindings altered!) in order to be
> able to reuse code.
>
> Thierry


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