Re: [PATCH] drm/panel: Add display timing for Okaya RS800480T-7X0GP

[Thierry Reding <thierry.reding@gmail.com>]

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On Sat, Jun 06, 2015 at 11:00:21PM +0200, Gary Bisson wrote:
> Thierry, All,
> 
> On Fri, Jun 5, 2015 at 2:28 PM, Thierry Reding <thierry.reding@gmail.com> wrote:
> > On Thu, May 28, 2015 at 05:37:46PM +0200, Gary Bisson wrote:
> >> Add support for the Okaya RS800480T-7X0GP to the DRM simple panel
> >> driver.
> >>
> >> The RS800480T-7X0GP is a WVGA (800x480) panel with an 18-bit parallel
> >> LCD interface. It supports pixel clocks in the range of 30-40 MHz.
> >>
> >> This panel details can be found at:
> >> http://boundarydevices.com/product/7-800x480-display/
> >>
> >> Signed-off-by: Gary Bisson <gary.bisson@boundarydevices.com>
> >> ---
> >> Hi all,
> >>
> >> This patch is the follow-up of a request from Philipp to add the Okaya display
> >> to the simple panel driver.
> >> http://lists.infradead.org/pipermail/linux-arm-kernel/2015-May/346657.html
> >>
> >> Regards,
> >> Gary
> >> ---
> >>  .../bindings/panel/okaya,rs800480t_7x0gp.txt       |  7 ++++++
> >>  .../devicetree/bindings/vendor-prefixes.txt        |  1 +
> >>  drivers/gpu/drm/panel/panel-simple.c               | 27 ++++++++++++++++++++++
> >>  3 files changed, 35 insertions(+)
> >>  create mode 100644 Documentation/devicetree/bindings/panel/okaya,rs800480t_7x0gp.txt
> >>
> >> diff --git a/Documentation/devicetree/bindings/panel/okaya,rs800480t_7x0gp.txt b/Documentation/devicetree/bindings/panel/okaya,rs800480t_7x0gp.txt
> >> new file mode 100644
> >> index 0000000..f7c729d
> >> --- /dev/null
> >> +++ b/Documentation/devicetree/bindings/panel/okaya,rs800480t_7x0gp.txt
> >> @@ -0,0 +1,7 @@
> >> +OKAYA Electric America, Inc. RS800480T-7X0GP 7" WVGA LCD panel
> >> +
> >> +Required properties:
> >> +- compatible: should be "okaya,rs800480t_7x0gp"
> >> +
> >> +This binding is compatible with the simple-panel binding, which is specified
> >> +in simple-panel.txt in this directory.
> >> diff --git a/Documentation/devicetree/bindings/vendor-prefixes.txt b/Documentation/devicetree/bindings/vendor-prefixes.txt
> >> index 4f35a00..06ce91c 100644
> >> --- a/Documentation/devicetree/bindings/vendor-prefixes.txt
> >> +++ b/Documentation/devicetree/bindings/vendor-prefixes.txt
> >> @@ -145,6 +145,7 @@ nintendo  Nintendo
> >>  nokia        Nokia
> >>  nvidia       NVIDIA
> >>  nxp  NXP Semiconductors
> >> +okaya        OKAYA Electric America, Inc.
> >>  onnn ON Semiconductor Corp.
> >>  opencores    OpenCores.org
> >>  ortustech    Ortus Technology Co., Ltd.
> >
> > Can you split this change into a separate patch? It needs an Acked-by
> > from one of the device tree binding maintainers, so make sure to Cc them
> > when you repost. scripts/get_maintainer.pl will list them for you.
> 
> Sure, will do.
> 
> >> +static const struct display_timing okaya_rs800480t_7x0gp_timing = {
> >> +     .pixelclock = { 30000000, 30000000, 40000000 },
> >> +     .hactive = { 800, 800, 800 },
> >> +     .hfront_porch = { 40, 40, 40 },
> >> +     .hback_porch = { 40, 40, 40 },
> >> +     .hsync_len = { 1, 48, 48 },
> >> +     .vactive = { 480, 480, 480 },
> >> +     .vfront_porch = { 13, 13, 13 },
> >> +     .vback_porch = { 29, 29, 29 },
> >> +     .vsync_len = { 3, 3, 3 },
> >
> > It strikes me as odd that the porches and VSYNC width should be fixed
> > for the panel. Is this really the case?
> 
> Well this is the values provided by Okaya. Here is a link to the
> datasheet, details are located in page 8:
> http://boundarydevices.com/datasheets/RS800480T-7X0GP-A.pdf

The way I read this the cells marked with - don't specify that a value
is the same as typical but rather that nobody determined that value.
It's unfortunate because it doesn't give us a good specification of the
timings, but I would suspect that the panel operates perfectly fine if
you use porches and sync pulse widths outside of the above range.

That said, I think it's fine to go with the above until we encounter
display hardware that can't match these constraints.

Thierry

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