From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: "Javier Martinez Canillas" <javierm@redhat.com>,
"Michal Suchánek" <msuchanek@suse.de>,
"Arnd Bergmann" <arnd@arndb.de>
Cc: linux-fbdev@vger.kernel.org,
Thomas Zimmermann <tzimmermann@suse.de>,
David Airlie <airlied@linux.ie>, Helge Deller <deller@gmx.de>,
mark.cave-ayland@ilande.co.uk, linuxppc-dev@lists.ozlabs.org,
dri-devel@lists.freedesktop.org,
Paul Mackerras <paulus@samba.org>,
Maxime Ripard <maxime@cerno.tech>,
Daniel Vetter <daniel@ffwll.ch>,
Geert Uytterhoeven <geert@linux-m68k.org>,
sam@ravnborg.org
Subject: Re: [PATCH v4 5/5] drm/ofdrm: Support big-endian scanout buffers
Date: Mon, 17 Oct 2022 17:44:05 +1100 [thread overview]
Message-ID: <365fe5029716e589eaef71ababf27a459348f9ff.camel@kernel.crashing.org> (raw)
In-Reply-To: <de796dba-1e75-e5a8-a908-f0aed4e01fec@redhat.com>
On Thu, 2022-10-13 at 09:39 +0200, Javier Martinez Canillas wrote:
> > In absence of such test results I think the most reasonable thing is to
> > keep the logic that nobody complained about for 10+ years.
> >
>
> I agree with Michal and Thomas on this. I don't see a strong reason to not
> use the same heuristic that the offb fbdev driver has been doing for this.
>
> Otherwise if this turns out to be needed, it will cause a regression for a
> user that switches to this driver instead. Specially since both fbdev and
> DRM drivers match against the same "display" OF compatible string.
I agree.
In the end, what it boils down to is, we don't know, we should guess. The
endianness of the kernel is as good a guess as anything here.
If not that, then assume BE.
That code was originally written for old macs. Those could simply not boot
anything other than a BE kernel. OF would always setup a 8bpp fb (so endianness
is irrelevant) but BootX could setup something else.
There's almost no old LE powerpc system out there, and I'm reasonably sure
actually none of any relevance to this code.
That leaves us with newer systems capable of endian switching. Those should just
get the property added.
I don't know of many cases out there. There' SLOS on powerpc which still won't
set it (which is what qemu uses). That could just be fixed. In the meantime
it makes sense for the kernel to follow its existing behaviour.
Cheers,
Ben.
WARNING: multiple messages have this Message-ID (diff)
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: "Javier Martinez Canillas" <javierm@redhat.com>,
"Michal Suchánek" <msuchanek@suse.de>,
"Arnd Bergmann" <arnd@arndb.de>
Cc: Thomas Zimmermann <tzimmermann@suse.de>,
David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
Helge Deller <deller@gmx.de>, Maxime Ripard <maxime@cerno.tech>,
sam@ravnborg.org, Michael Ellerman <mpe@ellerman.id.au>,
Paul Mackerras <paulus@samba.org>,
Geert Uytterhoeven <geert@linux-m68k.org>,
mark.cave-ayland@ilande.co.uk, linux-fbdev@vger.kernel.org,
linuxppc-dev@lists.ozlabs.org, dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v4 5/5] drm/ofdrm: Support big-endian scanout buffers
Date: Mon, 17 Oct 2022 17:44:05 +1100 [thread overview]
Message-ID: <365fe5029716e589eaef71ababf27a459348f9ff.camel@kernel.crashing.org> (raw)
In-Reply-To: <de796dba-1e75-e5a8-a908-f0aed4e01fec@redhat.com>
On Thu, 2022-10-13 at 09:39 +0200, Javier Martinez Canillas wrote:
> > In absence of such test results I think the most reasonable thing is to
> > keep the logic that nobody complained about for 10+ years.
> >
>
> I agree with Michal and Thomas on this. I don't see a strong reason to not
> use the same heuristic that the offb fbdev driver has been doing for this.
>
> Otherwise if this turns out to be needed, it will cause a regression for a
> user that switches to this driver instead. Specially since both fbdev and
> DRM drivers match against the same "display" OF compatible string.
I agree.
In the end, what it boils down to is, we don't know, we should guess. The
endianness of the kernel is as good a guess as anything here.
If not that, then assume BE.
That code was originally written for old macs. Those could simply not boot
anything other than a BE kernel. OF would always setup a 8bpp fb (so endianness
is irrelevant) but BootX could setup something else.
There's almost no old LE powerpc system out there, and I'm reasonably sure
actually none of any relevance to this code.
That leaves us with newer systems capable of endian switching. Those should just
get the property added.
I don't know of many cases out there. There' SLOS on powerpc which still won't
set it (which is what qemu uses). That could just be fixed. In the meantime
it makes sense for the kernel to follow its existing behaviour.
Cheers,
Ben.
WARNING: multiple messages have this Message-ID (diff)
From: Benjamin Herrenschmidt <benh@kernel.crashing.org>
To: "Javier Martinez Canillas" <javierm@redhat.com>,
"Michal Suchánek" <msuchanek@suse.de>,
"Arnd Bergmann" <arnd@arndb.de>
Cc: linux-fbdev@vger.kernel.org,
Thomas Zimmermann <tzimmermann@suse.de>,
David Airlie <airlied@linux.ie>,
Michael Ellerman <mpe@ellerman.id.au>,
Helge Deller <deller@gmx.de>,
mark.cave-ayland@ilande.co.uk, linuxppc-dev@lists.ozlabs.org,
dri-devel@lists.freedesktop.org,
Paul Mackerras <paulus@samba.org>,
Maxime Ripard <maxime@cerno.tech>,
Geert Uytterhoeven <geert@linux-m68k.org>,
sam@ravnborg.org
Subject: Re: [PATCH v4 5/5] drm/ofdrm: Support big-endian scanout buffers
Date: Mon, 17 Oct 2022 17:44:05 +1100 [thread overview]
Message-ID: <365fe5029716e589eaef71ababf27a459348f9ff.camel@kernel.crashing.org> (raw)
In-Reply-To: <de796dba-1e75-e5a8-a908-f0aed4e01fec@redhat.com>
On Thu, 2022-10-13 at 09:39 +0200, Javier Martinez Canillas wrote:
> > In absence of such test results I think the most reasonable thing is to
> > keep the logic that nobody complained about for 10+ years.
> >
>
> I agree with Michal and Thomas on this. I don't see a strong reason to not
> use the same heuristic that the offb fbdev driver has been doing for this.
>
> Otherwise if this turns out to be needed, it will cause a regression for a
> user that switches to this driver instead. Specially since both fbdev and
> DRM drivers match against the same "display" OF compatible string.
I agree.
In the end, what it boils down to is, we don't know, we should guess. The
endianness of the kernel is as good a guess as anything here.
If not that, then assume BE.
That code was originally written for old macs. Those could simply not boot
anything other than a BE kernel. OF would always setup a 8bpp fb (so endianness
is irrelevant) but BootX could setup something else.
There's almost no old LE powerpc system out there, and I'm reasonably sure
actually none of any relevance to this code.
That leaves us with newer systems capable of endian switching. Those should just
get the property added.
I don't know of many cases out there. There' SLOS on powerpc which still won't
set it (which is what qemu uses). That could just be fixed. In the meantime
it makes sense for the kernel to follow its existing behaviour.
Cheers,
Ben.
next prev parent reply other threads:[~2022-10-17 6:51 UTC|newest]
Thread overview: 53+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-09-28 10:50 [PATCH v4 0/5] drm: Add driver for PowerPC OF displays Thomas Zimmermann
2022-09-28 10:50 ` Thomas Zimmermann
2022-09-28 10:50 ` [PATCH v4 1/5] drm/ofdrm: Add ofdrm for Open Firmware framebuffers Thomas Zimmermann
2022-09-28 10:50 ` Thomas Zimmermann
2022-09-28 10:50 ` [PATCH v4 2/5] drm/ofdrm: Add CRTC state Thomas Zimmermann
2022-09-28 10:50 ` Thomas Zimmermann
2022-09-28 10:50 ` [PATCH v4 3/5] drm/ofdrm: Add per-model device function Thomas Zimmermann
2022-09-28 10:50 ` Thomas Zimmermann
2022-09-28 10:50 ` [PATCH v4 4/5] drm/ofdrm: Support color management Thomas Zimmermann
2022-09-28 10:50 ` Thomas Zimmermann
2022-09-28 10:50 ` [PATCH v4 5/5] drm/ofdrm: Support big-endian scanout buffers Thomas Zimmermann
2022-09-28 10:50 ` Thomas Zimmermann
2022-09-28 11:12 ` Michal Suchánek
2022-09-28 11:12 ` Michal Suchánek
2022-09-28 11:12 ` Michal Suchánek
2022-09-28 11:30 ` Thomas Zimmermann
2022-09-28 11:30 ` Thomas Zimmermann
2022-09-28 11:30 ` Thomas Zimmermann
2022-10-11 7:46 ` Javier Martinez Canillas
2022-10-11 11:30 ` Thomas Zimmermann
2022-10-11 20:06 ` Arnd Bergmann
2022-10-11 21:38 ` Michal Suchánek
2022-10-11 21:38 ` Michal Suchánek
2022-10-11 21:38 ` Michal Suchánek
2022-10-12 6:29 ` Arnd Bergmann
2022-10-12 7:23 ` Michal Suchánek
2022-10-12 6:46 ` Thomas Zimmermann
2022-10-12 7:17 ` Arnd Bergmann
2022-10-12 7:40 ` Thomas Zimmermann
2022-10-12 7:44 ` Arnd Bergmann
2022-10-12 8:27 ` Thomas Zimmermann
2022-10-12 8:38 ` Arnd Bergmann
2022-10-12 12:00 ` Thomas Zimmermann
2022-10-12 13:12 ` Arnd Bergmann
2022-10-12 14:27 ` Michal Suchánek
2022-10-12 14:27 ` Michal Suchánek
2022-10-12 14:27 ` Michal Suchánek
2022-10-13 7:39 ` Javier Martinez Canillas
2022-10-13 7:39 ` Javier Martinez Canillas
2022-10-13 7:39 ` Javier Martinez Canillas
2022-10-17 6:44 ` Benjamin Herrenschmidt [this message]
2022-10-17 6:44 ` Benjamin Herrenschmidt
2022-10-17 6:44 ` Benjamin Herrenschmidt
2022-10-12 14:31 ` Thomas Zimmermann
2022-10-12 14:59 ` Ville Syrjälä
2022-10-12 14:59 ` Ville Syrjälä
2022-10-12 14:59 ` Ville Syrjälä
2022-10-12 16:01 ` Michal Suchánek
2022-10-12 16:01 ` Michal Suchánek
2022-10-12 16:01 ` Michal Suchánek
2022-10-12 12:07 ` Michal Suchánek
2022-10-12 12:07 ` Michal Suchánek
2022-10-12 12:07 ` Michal Suchánek
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