Re: [PATCH 1/3] drm/panel: simple: Add ability to override typical timing

[Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>]

On Tue, Feb 6, 2018 at 10:56 AM, Sean Paul <seanpaul-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org> wrote:
> This patch adds the ability to override the typical display timing for a
> given panel. This is useful for devices which have timing constraints
> that do not apply across the entire display driver (eg: to avoid
> crosstalk between panel and digitizer on certain laptops). The rules are
> as follows:
>
> - panel must not specify fixed mode (since the override mode will
>   either be the same as the fixed mode, or we'll be unable to
>   check the bounds of the overried)
> - panel must specify at least one display_timing range which will be
>   used to ensure the override mode fits within its bounds
>
> Cc: Doug Anderson <dianders-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
> Cc: Heiko Stuebner <heiko-4mtYJXux2i+zQB+pC5nmwQ@public.gmane.org>
> Cc: Jeffy Chen <jeffy.chen-TNX95d0MmH7DzftRWevZcw@public.gmane.org>
> Cc: Rob Herring <robh+dt-DgEjT+Ai2ygdnm+yROfE0A@public.gmane.org>
> Cc: Stéphane Marchesin <marcheu-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
> Cc: Thierry Reding <thierry.reding-Re5JQEeQqe8AvxtiuMwx3w@public.gmane.org>
> Cc: devicetree-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
> Cc: dri-devel-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org
> Cc: linux-rockchip-IAPFreCvJWM7uuMidbF8XUB+6BGkLq7r@public.gmane.org
> Signed-off-by: Sean Paul <seanpaul-F7+t8E8rja9g9hUCZPvPmw@public.gmane.org>
> ---
>  .../bindings/display/panel/simple-panel.txt        | 20 +++++++

The binding should be a separate patch.

>  drivers/gpu/drm/panel/panel-simple.c               | 69 +++++++++++++++++++++-
>  2 files changed, 88 insertions(+), 1 deletion(-)
>
> diff --git a/Documentation/devicetree/bindings/display/panel/simple-panel.txt b/Documentation/devicetree/bindings/display/panel/simple-panel.txt
> index 16d8ff088b7d..590bbff6fc90 100644
> --- a/Documentation/devicetree/bindings/display/panel/simple-panel.txt
> +++ b/Documentation/devicetree/bindings/display/panel/simple-panel.txt
> @@ -7,6 +7,14 @@ Optional properties:
>  - ddc-i2c-bus: phandle of an I2C controller used for DDC EDID probing
>  - enable-gpios: GPIO pin to enable or disable the panel
>  - backlight: phandle of the backlight device attached to the panel
> +- override-mode: For devices which require a mode which differs from the

This is not a property, but a node so it needs its own section.

Also, it's not real clear from display-timing.txt, but the modes
should be grouped under a display-timings node. Looks like we haven't
been good at enforcing that as "panel-timing" is also common when
there's a single mode. I'd rather not have another way. With a
standard node name, we can validate the node more easily.

We'd lose the fact that this is explicitly an override, but I'd doubt
Thierry is going to start letting in panels with no timings.

Finally, since this is an override, is it valid to only override the
parameters that need overriding? I don't really have an opinion either
way. It just needs to be explicitly documented.

> +                display_timing's "typical" mode, and whose restrictions cannot
> +                be applied across the entire platform. The mode must fall
> +                within the bounds of the panel's specified display_timing, and
> +                cannot be used if the panel already specifies a single fixed
> +                mode. The format is specified under "timing subnode" in
> +                display-timing.txt
> +
>
>  Example:
>
> @@ -18,4 +26,16 @@ Example:
>                 enable-gpios = <&gpio 90 0>;
>
>                 backlight = <&backlight>;
> +
> +               override-mode {
> +                       clock-frequency = <266604720>;
> +                       hactive = <2400>;
> +                       hfront-porch = <48>;
> +                       hback-porch = <84>;
> +                       hsync-len = <32>;
> +                       vactive = <1600>;
> +                       vfront-porch = <3>;
> +                       vback-porch = <120>;
> +                       vsync-len = <10>;
> +               }
>         };
--
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