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

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Date:	Thu, 08 Oct 2015 21:15:00 +0200
From:	Robert Jarzmik <robert.jarzmik@...e.fr>
To:	Rob Herring <robh@...nel.org>,
	Philipp Zabel <philipp.zabel@...il.com>
Cc:	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	"devicetree\@vger.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel\@vger.kernel.org" <linux-kernel@...r.kernel.org>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	"linux-fbdev\@vger.kernel.org" <linux-fbdev@...r.kernel.org>
Subject: Re: [PATCH v2] video: fbdev: add Marvell PXA framebuffer binding

Rob Herring <robh@...nel.org> writes:

>> The pxafb driver acts today on the subset of registers which are the same across
>> all pxaXXX variants. This is what made me think only one compatible property was
>> required.
>>
>> If I'm wrong, I could add "marvell,pxa3xx-lcdc", is that what you think I should
>> do ?
>
> I would prefer specific compatibles (e.g. marvell,pxa270-lcdc) in
> addition to a generic one. You never know when a specific chip will
> have some quirk even though "the IP is the same".
Okay.

>> 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.
>
>>       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.

Cheers.

-- 
Robert
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