Re: [PATCH v2] video: fbdev: add Marvell PXA framebuffer binding

On Thu, Oct 8, 2015 at 2:15 PM, Robert Jarzmik [off-list ref] wrote:

Rob Herring [off-list ref] writes:

quoted

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And then, when a board maintainer will create a devicetree description, he will
write something like :
      compatible = "toshiba,ltm0305a776";
      compatible = "marvell,pxa2xx-panel";

Drop this compatible.

quoted

      lcd-type = "color-tft";
      ...

If that's the case, I wonder how to "enforce" that a panel used with
marvell,pxa2xx-lcdc (through the of_graph 'port' node) be compatible with
marvell,pxa2xx-panel ?

I'm not sure what you mean. Putting the panel into the dts ensures
that. The FB driver may check for toshiba,ltm0305a776 or a list of
panels. However, a DRM driver would probably not check that.

Rob

What I mean is that the LDLC controller _must_ be programmmed with the correct
panel type, ie. one register of the LDLC should be set according to this type.

The type is a hardware property of the panel, and yet it is absolutely mandatory
to have it set in the panel.

What I mean is : what is the good way to enforce that this property is set
somewhere in the devicetree description ? Philipp adviced for it to be transfered
to the ldlc description (ie. marvell,pxa2xx-ldlc), while I was thinking of
having it in a panel description.

Either of those options are fine. Neither should need
marvell,pxa2xx-panel though. I'd lean towards putting it in the panel,
but in that case it should be generic for panels which I think it is.
It should probably be optional with not present meaning color-tft
(since every other type is practically dead), but you could say
required on pxa2xx.

The only way to enforce it ATM, is panicking or something if the LCDC
finds it is not set. That's not any worse that checking for
marvell,pxa2xx-panel.

Rob