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

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Message-ID: <CAKMK7uHxjmZShgzVdt6yPRN6qN4QVMvwCfNYxTp8yWdfs4x_ng@mail.gmail.com>
Date:   Thu, 20 Jan 2022 12:40:49 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Daniel Palmer <daniel@...f.com>
Cc:     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

On Thu, Jan 20, 2022 at 12:12 PM Daniel Palmer <daniel@...f.com> wrote:
>
> 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.

Move to drm kms, fix userspace. fbdev never supported this, and I
really don't think it's a good idea to add in-kernel rotation to
fbdev.
-Daniel

>
> Cheers,
>
> Daniel
>
> 0 - https://twitter.com/linux_chenxing/status/1479801511274491909



-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch