[PATCH 3/3] ARM: dts: Add display timing node to exynos5250-arndale.dts

[Tomasz Figa]

On Friday 10 of May 2013 11:57:34 Vikas Sajjan wrote:
> Hi Olof,
> 
> On 10 May 2013 11:51, Vikas Sajjan <vikas.sajjan at linaro.org> wrote:
> > Hi Olof,
> > 
> > On 10 May 2013 11:08, Olof Johansson <olof at lixom.net> wrote:
> >> On Thu, May 9, 2013 at 7:55 PM, Vikas Sajjan
> >> <vikas.sajjan at linaro.org>
> >> 
> >> wrote:
> >> > Hi Tomasz,
> >> > 
> >> > On 10 May 2013 05:35, Tomasz Figa <tomasz.figa at gmail.com> wrote:
> >> >> Hi Vikas,
> >> >> 
> >> >> On Wednesday 08 of May 2013 11:31:34 Vikas Sajjan wrote:
> >> >> > Adds display timing node for a DP panel to Arndale Board DTS
> >> >> > file
> >> >> > 
> >> >> > Signed-off-by: Vikas Sajjan <vikas.sajjan at linaro.org>
> >> >> > ---
> >> >> > 
> >> >> >  arch/arm/boot/dts/exynos5250-arndale.dts |   16
> >> >> >  ++++++++++++++++
> >> >> >  1 file changed, 16 insertions(+)
> >> >> > 
> >> >> > diff --git a/arch/arm/boot/dts/exynos5250-arndale.dts
> >> >> > b/arch/arm/boot/dts/exynos5250-arndale.dts index
> >> >> > f68b820..c831a5c
> >> >> > 100644
> >> >> > --- a/arch/arm/boot/dts/exynos5250-arndale.dts
> >> >> > +++ b/arch/arm/boot/dts/exynos5250-arndale.dts
> >> >> > @@ -459,4 +459,20 @@
> >> >> > 
> >> >> >               samsung,lane-count = <4>;
> >> >> >       
> >> >> >       };
> >> >> > 
> >> >> > +     display-timings {
> >> >> > +             native-mode = <&timing0>;
> >> >> > +             timing0: timing at 0 {
> >> >> > +                     /* 2560x1600 DP panel */
> >> >> > +                     clock-frequency = <50000>;
> >> >> > +                     hactive = <2560>;
> >> >> > +                     vactive = <1600>;
> >> >> > +                     hfront-porch = <48>;
> >> >> > +                     hback-porch = <80>;
> >> >> > +                     hsync-len = <32>;
> >> >> > +                     vback-porch = <16>;
> >> >> > +                     vfront-porch = <8>;
> >> >> > +                     vsync-len = <6>;
> >> >> > +             };
> >> >> > +     };
> >> >> 
> >> >> What display are those timings used for? Shouldn't they be placed
> >> 
> >> inside
> >> 
> >> >> node of that display?
> >> > 
> >> > This timing information will be used parsed by the FIMD probe with
> >> > the
> >> 
> >> help
> >> 
> >> > of "Video Helper function"  as done in this link
> >> 
> >> https://git.kernel.org/cgit/linux/kernel/git/daeinki/drm-exynos.git/c
> >> ommit/?h=exynos-drm-next&id=7f4596f4aebcc9fcf2d50d3fe398508d710c4dd0
> >> 
> >> That function passes in a device node pointer to the FIMD device
> >> node,
> >> and only looks for a display-timings node under there. Tomasz is
> >> right, as far as I can tell.
> >> 
> >> Placing display timings at the root of the device tree seems
> >> completely
> >> wrong.
> >> 
> >>         I referred this "
> 
> Documentation/devicetree/bindings/video/display-timing.txt" for example
> 
>             here it dosen't mention about whether display timings node
> can be placed at the root of the device tree or NOT.
>  Not sure how we should be placing the node then.

I think this is pretty obvious.

Imagine a bit more complex case: a board has two video outputs (let's say 
FIMD0 and FIMD1), each connected to a completely different display. This 
means that each display needs different timings.

How would you know which timings to use if all of them were be placed 
under the root node?

Best regards,
Tomasz