linux-kernel - Re: [PATCH 00/26] drm/omap: Convert to use videomode from omap_video

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Date:   Thu, 15 Dec 2016 09:56:28 +0200
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        <dri-devel@...ts.freedesktop.org>
CC:     Peter Ujfalusi <peter.ujfalusi@...com>, <thierry.reding@...il.com>,
        <airlied@...ux.ie>, Mark Rutland <mark.rutland@....com>,
        <devicetree@...r.kernel.org>, <daniel.vetter@...ll.ch>,
        <linux-kernel@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>
Subject: Re: [PATCH 00/26] drm/omap: Convert to use videomode from
 omap_video_timings

On 14/12/16 23:32, Laurent Pinchart wrote:
> Hi Peter,
> 
> On Thursday 01 Sep 2016 14:22:54 Peter Ujfalusi wrote:
>> Hi,
>>
>> The following series will convert the omapdrm stack to use the generic
>> videmode instead of the private omap_video_timings struct for the panel
>> information.
>>
>> Since we have several panels under omapdrm/displays/ where the data drive
>> edge is set to be different then the sync drive edge, the first three patch
>> will add support to select the sync drive edge via DT.
>> I was not able to locate the datasheet for all the panels and because the
>> different edge was used in omapdrm and omapfb for a long time without
>> complains from users - and they were written this way - I think it is a
>> valid that we can have panels requiring different edge for data and sync to
>> be driven.
> 
> That's very peculiar. Have you been able to locate at least one panel 
> datasheet that documents this requirement ?

I think I remember seeing some panel or encoder asking for different
edges. But it's rather vague memory =).

Interestingly, the default behavior of OMAP DSS is to have data and sync
at different edges. I don't know what was the rationale for that design.

Another, slightly related, interesting thing is that only from OMAP4
forward we have had the possibility to have hsync and vsync happen at
the same time. Earlier hsync came first, followed by vsync. This old
behavior caused problems at least on one encoder I worked on.

 Tomi



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