From: Javier Martinez Canillas <javierm@redhat.com>
To: "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>,
benh@kernel.crashing.org, 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: Thu, 13 Oct 2022 09:39:21 +0200 [thread overview]
Message-ID: <de796dba-1e75-e5a8-a908-f0aed4e01fec@redhat.com> (raw)
In-Reply-To: <20221012142707.GD28810@kitsune.suse.cz>
Hello,
On 10/12/22 16:27, Michal Suchánek wrote:
[...]
>>
>> If you are using the framebuffer code from vga.c, I would guess that
>> that you can run a big-endian kernel with qemu-system-ppc64,
>> or a little-endian kernel with qemu-system-ppc64le and get the
>> correct colors, while running a little-endian kernel with
>> qemu-system-ppc64 and vga.c, or using a different framebuffer
>> emulation on a big-endian kernel would give you the wrong colors.
>
> Thanks for digging this up.
>
> That makes one thing clear: qemu does not emulate this framebuffer
> property correctly, and cannot be relied on for verification.
>
> If you can provide test results from real hardware that show the current
> logic as flawed it should be changed.
>
> 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.
--
Best regards,
Javier Martinez Canillas
Core Platforms
Red Hat
WARNING: multiple messages have this Message-ID (diff)
From: Javier Martinez Canillas <javierm@redhat.com>
To: "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: Thu, 13 Oct 2022 09:39:21 +0200 [thread overview]
Message-ID: <de796dba-1e75-e5a8-a908-f0aed4e01fec@redhat.com> (raw)
In-Reply-To: <20221012142707.GD28810@kitsune.suse.cz>
Hello,
On 10/12/22 16:27, Michal Suchánek wrote:
[...]
>>
>> If you are using the framebuffer code from vga.c, I would guess that
>> that you can run a big-endian kernel with qemu-system-ppc64,
>> or a little-endian kernel with qemu-system-ppc64le and get the
>> correct colors, while running a little-endian kernel with
>> qemu-system-ppc64 and vga.c, or using a different framebuffer
>> emulation on a big-endian kernel would give you the wrong colors.
>
> Thanks for digging this up.
>
> That makes one thing clear: qemu does not emulate this framebuffer
> property correctly, and cannot be relied on for verification.
>
> If you can provide test results from real hardware that show the current
> logic as flawed it should be changed.
>
> 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.
--
Best regards,
Javier Martinez Canillas
Core Platforms
Red Hat
WARNING: multiple messages have this Message-ID (diff)
From: Javier Martinez Canillas <javierm@redhat.com>
To: "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: Thu, 13 Oct 2022 09:39:21 +0200 [thread overview]
Message-ID: <de796dba-1e75-e5a8-a908-f0aed4e01fec@redhat.com> (raw)
In-Reply-To: <20221012142707.GD28810@kitsune.suse.cz>
Hello,
On 10/12/22 16:27, Michal Suchánek wrote:
[...]
>>
>> If you are using the framebuffer code from vga.c, I would guess that
>> that you can run a big-endian kernel with qemu-system-ppc64,
>> or a little-endian kernel with qemu-system-ppc64le and get the
>> correct colors, while running a little-endian kernel with
>> qemu-system-ppc64 and vga.c, or using a different framebuffer
>> emulation on a big-endian kernel would give you the wrong colors.
>
> Thanks for digging this up.
>
> That makes one thing clear: qemu does not emulate this framebuffer
> property correctly, and cannot be relied on for verification.
>
> If you can provide test results from real hardware that show the current
> logic as flawed it should be changed.
>
> 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.
--
Best regards,
Javier Martinez Canillas
Core Platforms
Red Hat
next prev parent reply other threads:[~2022-10-13 7:39 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 [this message]
2022-10-13 7:39 ` Javier Martinez Canillas
2022-10-13 7:39 ` Javier Martinez Canillas
2022-10-17 6:44 ` Benjamin Herrenschmidt
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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