linux-kernel - Re: [EXT] Re: [PATCH v2 09/15] dt-bindings: display: Add max-res property for mxsfb

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Message-ID: <1565781243.3209.55.camel@nxp.com>
Date:   Wed, 14 Aug 2019 11:14:03 +0000
From:   Robert Chiras <robert.chiras@....com>
To:     "stefan@...er.ch" <stefan@...er.ch>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>
CC:     dl-linux-imx <linux-imx@....com>, "marex@...x.de" <marex@...x.de>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "agx@...xcpu.org" <agx@...xcpu.org>,
        "festevam@...il.com" <festevam@...il.com>,
        "daniel@...ll.ch" <daniel@...ll.ch>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "airlied@...ux.ie" <airlied@...ux.ie>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>
Subject: Re: [EXT] Re: [PATCH v2 09/15] dt-bindings: display: Add max-res
 property for mxsfb

Hi Stefan,
On Mi, 2019-08-14 at 13:03 +0200, Stefan Agner wrote:
> On 2019-08-14 12:48, Robert Chiras wrote:
> > 
> > Add new optional property 'max-res', to limit the maximum supported
> > resolution by the MXSFB_DRM driver.
> I would also mention the reason why we need this.
> 
> I guess this needs a vendor prefix as well (fsl,max-res). I also
> would
> like to have the ack of the device tree folks here.
Rob Herring also aked be about this, and I'll copy here the reply, with
explanations:

Indeed, this limitation is actually due to bandwidth limitation, but
the problem is that this limitation comes on i.MX8M (known as mScale
850D), where the memory bandwidth cannot support: GPU/VPU workload in
the same time with both DCSS driving 4k@60 and eLCDIF driving 1080p@60.
Since eLCDIF is a secondary display we though to add the posibility to
limit it's bandwidth by limiting the resolution.
If you say that more details are needed, I can add them in the
description.
> 
> --
> Stefan
> 
> > 
> > 
> > Signed-off-by: Robert Chiras <robert.chiras@....com>
> > ---
> >  Documentation/devicetree/bindings/display/mxsfb.txt | 6 ++++++
> >  1 file changed, 6 insertions(+)
> > 
> > diff --git a/Documentation/devicetree/bindings/display/mxsfb.txt
> > b/Documentation/devicetree/bindings/display/mxsfb.txt
> > index 472e1ea..55e22ed 100644
> > --- a/Documentation/devicetree/bindings/display/mxsfb.txt
> > +++ b/Documentation/devicetree/bindings/display/mxsfb.txt
> > @@ -17,6 +17,12 @@ Required properties:
> >  Required sub-nodes:
> >    - port: The connection to an encoder chip.
> > 
> > +Optional properties:
> > +- max-res:   an array with a maximum of two integers, representing
> > the
> > +             maximum supported resolution, in the form of
> > +             <maxX>, <maxY>; if one of the item is <0>, the
> > default
> > +             driver-defined maximum resolution for that axis is
> > used
> > +
> >  Example:
> > 
> >       lcdif1: display-controller@...0000 {

Thanks,
Robert