Date:   Mon, 22 Nov 2021 12:39:38 +0200
From:   Pekka Paalanen <ppaalanen@gmail.com>
To:     Hector Martin <marcan@marcan.st>
Cc:     Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
        Maxime Ripard <mripard@kernel.org>,
        Thomas Zimmermann <tzimmermann@suse.de>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>,
        dri-devel@lists.freedesktop.org,
        Alyssa Rosenzweig <alyssa@rosenzweig.io>,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH 2/3] drm/format-helper: Add
 drm_fb_xrgb8888_to_xrgb2101010_dstclip()
Message-ID: <20211122123938.47fcbef0@eldfell>
In-Reply-To: <7e1356b9-3122-e169-193e-37547a50499a@marcan.st>
References: <20211117145829.204360-1-marcan@marcan.st>
        <20211117145829.204360-3-marcan@marcan.st>
        <20211122115247.257f30fa@eldfell>
        <7e1356b9-3122-e169-193e-37547a50499a@marcan.st>
MIME-Version: 1.0
Content-Type: multipart/signed; boundary="Sig_/bjihys6S1XCiDosstpGx6b+";
 protocol="application/pgp-signature"; micalg=pgp-sha256
Precedence: bulk

--Sig_/bjihys6S1XCiDosstpGx6b+
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: quoted-printable

On Mon, 22 Nov 2021 19:05:16 +0900
Hector Martin <marcan@marcan.st> wrote:

> On 22/11/2021 18.52, Pekka Paalanen wrote:
> > On Wed, 17 Nov 2021 23:58:28 +0900
> > Hector Martin <marcan@marcan.st> wrote:
> >  =20
> >> Add XRGB8888 emulation support for devices that can only do XRGB210101=
0.
> >>
> >> This is chiefly useful for simpledrm on Apple devices where the
> >> bootloader-provided framebuffer is 10-bit, which already works fine wi=
th
> >> simplefb. This is required to make simpledrm support this too.
> >>
> >> Signed-off-by: Hector Martin <marcan@marcan.st>
> >> ---
> >>   drivers/gpu/drm/drm_format_helper.c | 64 +++++++++++++++++++++++++++=
++
> >>   include/drm/drm_format_helper.h     |  4 ++
> >>   2 files changed, 68 insertions(+) =20
> >=20
> > Hi Hector,
> >=20
> > I'm curious, since the bootloader seems to always set up a 10-bit mode,
> > is there a reason for it that you can guess? Is the monitor in WCG or
> > even HDR mode? =20
>=20
> My guess is that Apple prefer to use 10-bit framebuffers for seamless=20
> handover with their graphics stack, which presumably uses 10-bit=20
> framebuffers these days. It seems to be unconditional; I've never seen=20
> anything but 10 bits across all Apple devices, both with the internal=20
> panels on laptops and with bog standard external displays on the Mac=20
> Mini via HDMI. HDR is not necessary, even very dumb capture cards and=20
> old screens get a 10-bit framebufer in memory.

That makes perfect sense, thanks!

Switching between sRGB and WCG or HDR mode is not a modeset, it's just
HDMI/DP/whatever metadata/infoframe.

> The only time I see an 8-bit framebuffer is with *no* monitor connected=20
> on the Mini, in which case you get an 8-bit 640x1136 dummy framebuffer=20
> (that's the iPhone 5 screen resolution... :-) )
>=20

Thanks,
pq

--Sig_/bjihys6S1XCiDosstpGx6b+
Content-Type: application/pgp-signature
Content-Description: OpenPGP digital signature

-----BEGIN PGP SIGNATURE-----
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=wJTn
-----END PGP SIGNATURE-----

--Sig_/bjihys6S1XCiDosstpGx6b+--