linux-kernel - Re: [PATCH v7 1/2] video: ARM CLCD: Add DT support

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Date:	Mon, 23 Jun 2014 12:56:34 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Pawel Moll <pawel.moll@....com>
Cc:	Mark Rutland <Mark.Rutland@....com>,
	Rob Herring <robh+dt@...nel.org>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	Tomi Valkeinen <tomi.valkeinen@...com>,
	Russell King <rmk+kernel@....linux.org.uk>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-fbdev@...r.kernel.org" <linux-fbdev@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v7 1/2] video: ARM CLCD: Add DT support

On Mon, Jun 23, 2014 at 10:59 AM, Pawel Moll <pawel.moll@....com> wrote:
> On Mon, 2014-06-23 at 16:43 +0100, Rob Herring wrote:
>> On Mon, Jun 23, 2014 at 9:13 AM, Pawel Moll <pawel.moll@....com> wrote:
>> > On Fri, 2014-06-20 at 18:09 +0100, Mark Rutland wrote:

>> >> > +- max-memory-bandwidth: maximum bandwidth in bytes per second that the
>> >> > +   cell's memory interface can handle
>> >>
>> >> When should I set this, given it is optional?
>> >
>> > When there is a (significant) limitation of the bandwidth available for
>> > the cell's memory interface. One will either be told by the soc guys or
>> > will figure it out in the hard way, as we did :-(
>>
>> What are you going to do with this information? b/w is a function of
>> screen size and pixel depth. Are you going to refuse certain configs
>> based on that? Seems like someone doing their own modes should know
>> what they are doing and the limitations.
>>
>> Again, drop it until there is a defined need for this.
>
> Yes, there is. Use case: PL111 is wired up to a HDMI formatter, which
> will take everything up to 1080p. This is what a DRM driver (what/if
> it's ready) will get from the encoder driver (and rightly so). But the
> chip interconnect limitations is make the chip being able to get 480p at
> 60Hz tops.
>
> Or do you want me to add a subnode with timings for all achievable modes
> instead?

I want this solved in a generic way and not something pl111 specific.
If this is already defined then use it. If not, I would drop this for
now and get a pl111 binding in place finally.

Rob
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