linux-kernel - Re: [PATCH 0/4] drm/atmel-hlcdc: fix plane clipping/rotation issues

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Date:   Thu, 10 Jan 2019 21:16:36 +0100
From:   Sam Ravnborg <sam@...nborg.org>
To:     Boris Brezillon <bbrezillon@...nel.org>,
        Peter Rosin <peda@...ntia.se>
Cc:     Peter Rosin <peda@...ntia.se>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        David Airlie <airlied@...ux.ie>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Boris Brezillon <boris.brezillon@...tlin.com>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 0/4] drm/atmel-hlcdc: fix plane clipping/rotation issues

Hi Peter.

(Hijacking this thread as I lost the orginal mails)

> > 
> > I found an unfortunate issue while recoding plane handling to use
> > drm_atomic_helper_check_plane_state(). The driver rotates clockwise,
> > which is not correct. I simply fixed it (patch 1/4), but maybe that
> > will cause regressions for unsuspecting users who simply assumed
> > that the clockwise rotation was correct? I don't know what to do
> > about that? Adding an option to get the old broken behavior seems
> > useless, wouldn't it be just as easy to just fix whatever app to
> > rotate the other way instead of adding an option somewhere?
> 
> Hm, rotation support has been added before the standard rotation
> property was created, and at that time I assumed rotation was clockwise
> (which apparently was an unwise choice). Anyway, I don't have a
> solution for this problem, so I'll let Nicolas decide if it's
> acceptable to change the rotation behavior.
> 
> > 
> > I have only tested this series on sama5d3, but I did check the docs
> > for various other chips (sama5d2, sama5d4, sam9n12, sam9g15, sam9g35
> > and sam9x35) supported by the driver (relevant to patch 4/4).

I wonder if, when this code path is anyway touched, could benefit
from drm_rect_rotate().

It is obviously not a simple replacement, but could it be used then
I hope the resulting code is simpler.

	Sam