Re: [PATCH 1/3] dt-bindings: Add doc for the ingenic-drm driver

[Paul Cercueil]

Hi Sam, thanks for the feedback.

Le ven. 1 mars 2019 à 17:16, Sam Ravnborg <sam@xxxxxxxxxxxx> a écrit :
> Hi Paul.
>
> Good to see work migrating fbdev => drm.
>
> Following comments is based on experience while working on migrating
> another driver from fbdev => drm.
>
> On Thu, Feb 28, 2019 at 07:07:54PM -0300, Paul Cercueil wrote:
> >  Add documentation for the devicetree bindings of the DRM driver for 
> > the
> >  JZ47xx family of SoCs from Ingenic.
> >
> >  Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> >  Tested-by: Artur Rojek <contact@xxxxxxxxxxxxxx>
> >  ---
> >   .../devicetree/bindings/display/ingenic,drm.txt    | 30 
> > ++++++++++++++++++++++
> >   1 file changed, 30 insertions(+)
> >   create mode 100644 
> > Documentation/devicetree/bindings/display/ingenic,drm.txt
> >
> >  diff --git 
> > a/Documentation/devicetree/bindings/display/ingenic,drm.txt 
> > b/Documentation/devicetree/bindings/display/ingenic,drm.txt
> >  new file mode 100644
> >  index 000000000000..52a368ec35cd
> >  --- /dev/null
> >  +++ b/Documentation/devicetree/bindings/display/ingenic,drm.txt
> >  @@ -0,0 +1,30 @@
> >  +Ingenic JZ47xx DRM driver
> >  +
> >  +Required properties:
> >  +- compatible: one of:
> >  +  * ingenic,jz4740-drm
> >  +  * ingenic,jz4725b-drm
> >  +- reg: LCD registers location and length
> The fbdev way of doing this was to hardcode register setttings.
> In the drm world we read the configuration of the panel and let
> this decide the actual configuration.
>
> Note that no drm drivers supports stn displays and that there
> is really no use for this these days. So you can skip the STN parts.

STN panels aren't really my problem; but I have a board with a Sharp
LS020B1DD01D panel, which requires the LCD IP to be configured for a
"special 2" panel. I also have a board with a "smart" panel (ili9331)
that needs a special configuration in the IP. There is nothing in
the drm_panel interface that tells me what mode I should use for what
panel...

> Also the modern way to specify a panel in the DT is using OF graph 
> bindings.
> You can find many examples how to do this.

Ok, I was looking at the Tegra driver, which uses a "nvidia,panel" DT
property. I will change it to use the graph thing.

> I was there with the atmel LCDC driver (not in the kernel yet),
> and had some challenges with this.
>
> 	Sam

Thanks,
-Paul