From: Thomas Zimmermann <tzimmermann@suse.de>
To: Arnd Bergmann <arnd@arndb.de>,
Javier Martinez Canillas <javierm@redhat.com>,
David Airlie <airlied@linux.ie>, Daniel Vetter <daniel@ffwll.ch>,
Helge Deller <deller@gmx.de>,
maxime@cerno.tech, sam@ravnborg.org,
Michal Suchanek <msuchanek@suse.de>,
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
Cc: 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: Wed, 12 Oct 2022 09:40:07 +0200 [thread overview]
Message-ID: <866c7033-0d4e-7b5d-008c-8eb16f99498b@suse.de> (raw)
In-Reply-To: <654e3cfe-80d7-46c9-8e5e-461846e4df35@app.fastmail.com>
[-- Attachment #1.1: Type: text/plain, Size: 2097 bytes --]
Hi
Am 12.10.22 um 09:17 schrieb Arnd Bergmann:
> On Wed, Oct 12, 2022, at 8:46 AM, Thomas Zimmermann wrote:
>> Am 11.10.22 um 22:06 schrieb Arnd Bergmann:
>>> On Tue, Oct 11, 2022, at 1:30 PM, Thomas Zimmermann wrote:
>>>> Am 11.10.22 um 09:46 schrieb Javier Martinez Canillas:
>>>>>> +static bool display_get_big_endian_of(struct drm_device *dev, struct device_node *of_node)
>>>>>> +{
>>>>>> + bool big_endian;
>>>>>> +
>>>>>> +#ifdef __BIG_ENDIAN
>>>>>> + big_endian = true;
>>>>>> + if (of_get_property(of_node, "little-endian", NULL))
>>>>>> + big_endian = false;
>>>>>> +#else
>>>>>> + big_endian = false;
>>>>>> + if (of_get_property(of_node, "big-endian", NULL))
>>>>>> + big_endian = true;
>>>>>> +#endif
>>>>>> +
>>>>>> + return big_endian;
>>>>>> +}
>>>>>> +
>>>>>
>>>>> Ah, I see. The heuristic then is whether the build is BE or LE or if the Device
>>>>> Tree has an explicit node defining the endianess. The patch looks good to me:
>>>>
>>>> Yes. I took this test from offb.
>>>
>>> Has the driver been tested with little-endian kernels though? While
>>> ppc32 kernels are always BE, you can build kernels as either big-endian
>>> or little-endian for most (modern) powerpc64 and arm/arm64 hardware,
>>> and I don't see why that should change the defaults of the driver
>>> when describing the same framebuffer hardware.
>>
>> Yes, I tested this on qemu's ppc64le and ppc64.
>
> Does qemu mark the device has having a particular endianess then, or
> does it switch the layout of the framebuffer to match what the CPU
> does?
The latter. On neither architecture does qemu expose this flag. The
default endianess corresponds to the host.
Best regards
Thomas
>
> I've seen other cases where devices in qemu were defined using an
> arbitrary definition of "cpu-endian", which is generally not how
> real hardware works.
>
> Arnd
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev
[-- Attachment #2: OpenPGP digital signature --]
[-- Type: application/pgp-signature, Size: 840 bytes --]
next prev parent reply other threads:[~2022-10-12 7:41 UTC|newest]
Thread overview: 29+ 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 ` [PATCH v4 1/5] drm/ofdrm: Add ofdrm for Open Firmware framebuffers Thomas Zimmermann
2022-09-28 10:50 ` [PATCH v4 2/5] drm/ofdrm: Add CRTC state 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 ` [PATCH v4 4/5] drm/ofdrm: Support color management Thomas Zimmermann
2022-09-28 10:50 ` [PATCH v4 5/5] drm/ofdrm: Support big-endian scanout buffers Thomas Zimmermann
2022-09-28 11:12 ` Michal Suchánek
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
2022-10-12 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 [this message]
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
2022-10-13 7:39 ` Javier Martinez Canillas
2022-10-17 6:44 ` Benjamin Herrenschmidt
2022-10-12 14:31 ` Thomas Zimmermann
2022-10-12 14:59 ` Ville Syrjälä
2022-10-12 16:01 ` Michal Suchánek
2022-10-12 12:07 ` Michal Suchánek
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=866c7033-0d4e-7b5d-008c-8eb16f99498b@suse.de \
--to=tzimmermann@suse.de \
--cc=airlied@linux.ie \
--cc=arnd@arndb.de \
--cc=benh@kernel.crashing.org \
--cc=daniel@ffwll.ch \
--cc=deller@gmx.de \
--cc=dri-devel@lists.freedesktop.org \
--cc=geert@linux-m68k.org \
--cc=javierm@redhat.com \
--cc=linux-fbdev@vger.kernel.org \
--cc=linuxppc-dev@lists.ozlabs.org \
--cc=mark.cave-ayland@ilande.co.uk \
--cc=maxime@cerno.tech \
--cc=mpe@ellerman.id.au \
--cc=msuchanek@suse.de \
--cc=paulus@samba.org \
--cc=sam@ravnborg.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).