linux-kernel - Re: [RFC] How to add hardware rotation, scaling etc to a DRM/KMS driver

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Date:   Thu, 20 Jan 2022 20:15:40 +0900
From:   Daniel Palmer <daniel@...f.com>
To:     Daniel Palmer <daniel@...f.com>,
        Hans de Goede <j.w.r.degoede@...il.com>,
        dri-devel@...ts.freedesktop.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] How to add hardware rotation, scaling etc to a DRM/KMS driver

Hi Daniel,

On Thu, 20 Jan 2022 at 01:30, Daniel Vetter <daniel@...ll.ch> wrote:
> > I got the feeling that maybe I should just provide an interface to the
> > blitter from userspace and userspace should be doing the rotation. I'd
> > like to do it in the kernel so stuff like SDL1 apps just work but
> > maybe that isn't possible?
>
> panel orientation property is for that stuff:
> fbcon will head this and rotate in sw,

This is working. On boot I get Tux rotated correctly etc.

> as should any competent compositor
> in userspace (but some might not, it depends).

That's the problem I guess. I don't have one. SDL1 apps like prboom
use the fbdev emulation as-is so they render upside down[0].
I have 16MB of local storage and 128MB of RAM so I don't think I'll
manage to get the standard userland bits onto it.

I wanted to do the rotation in the kernel so I didn't have to hack up SDL1.

Cheers,

Daniel

0 - https://twitter.com/linux_chenxing/status/1479801511274491909