From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from cstnet.cn (smtp21.cstnet.cn [159.226.251.21]) (using TLSv1.2 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 787CB1E5B7B for ; Wed, 25 Feb 2026 07:46:01 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=159.226.251.21 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772005566; cv=none; b=q8sZosHKoxppmH/FfwOJR7FQwsF9TAYsc2eBvw7ssae6k6jZqbCru3m3siZgjv+VCZXEWW5gS9kA/AovhVpbCAGeJFP7253qke/IyVw7QBg8RslKBLXVKijwDVTscXF3Gn20ChBdUoTX8f9KgOsm4GNWgUeaeOb0/GbVZXmGKus= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1772005566; c=relaxed/simple; bh=GUHuWh5w+oWcLjGuatQVgO/SEyXsCEegBPl2uokhU2Y=; h=Message-ID:Subject:From:To:Cc:Date:In-Reply-To:References: Content-Type:MIME-Version; b=dYEauLQJZY+RLc00X85AMNYo8nlCE7ax8DCKiYHp4NskVbKfQDxLJU9vvD0sE8mQBNQmkfE9UJhC/VkntqRPOXc+/VwMXIrgI0bbX8AILcp11wgzINnxhvof/eNgBwhw6uAYJX8sI2JPM9oJ+txexBFye2un16foPiQDwv81wHo= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=iscas.ac.cn; spf=pass smtp.mailfrom=iscas.ac.cn; arc=none smtp.client-ip=159.226.251.21 Authentication-Results: smtp.subspace.kernel.org; dmarc=none (p=none dis=none) header.from=iscas.ac.cn Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=iscas.ac.cn Received: from edelgard.fodlan.icenowy.me (unknown [112.94.101.233]) by APP-01 (Coremail) with SMTP id qwCowABX_Wj8pp5p_OC2CA--.300S2; Wed, 25 Feb 2026 15:38:37 +0800 (CST) Message-ID: <35fba9692636a2f6ba9fabc8e67f5684a54b17f1.camel@iscas.ac.cn> Subject: Re: [PATCH] drm/dumb-buffers: document that it's only for linear FB From: Icenowy Zheng To: Thomas Zimmermann , Maarten Lankhorst , Maxime Ripard , David Airlie , Simona Vetter Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Date: Wed, 25 Feb 2026 15:38:36 +0800 In-Reply-To: <6515820a-3bb3-4868-9b30-9c1f80709ab2@suse.de> References: <20260225061315.1003811-1-zhengxingda@iscas.ac.cn> <6515820a-3bb3-4868-9b30-9c1f80709ab2@suse.de> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: quoted-printable User-Agent: Evolution 3.58.3 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 X-CM-TRANSID:qwCowABX_Wj8pp5p_OC2CA--.300S2 X-Coremail-Antispam: 1UD129KBjvJXoW7WF1DuFW8ur18GrWktr4kCrg_yoW8tFyfpF 4fKry2vr1DAFZayr1Du3Z8WFy5Za97XFWrCa4vy347ZF90yF1xWa18t3yYqF9rZrn7GFy2 qrnFgryrur1UAFJanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkab7Iv0xC_Kw4lb4IE77IF4wAFF20E14v26r4j6ryUM7CY07I2 0VC2zVCF04k26cxKx2IYs7xG6rWj6s0DM7CIcVAFz4kK6r1j6r18M28lY4IEw2IIxxk0rw A2F7IY1VAKz4vEj48ve4kI8wA2z4x0Y4vE2Ix0cI8IcVAFwI0_Xr0_Ar1l84ACjcxK6xII jxv20xvEc7CjxVAFwI0_Gr1j6F4UJwA2z4x0Y4vEx4A2jsIE14v26F4UJVW0owA2z4x0Y4 vEx4A2jsIEc7CjxVAFwI0_GcCE3s1le2I262IYc4CY6c8Ij28IcVAaY2xG8wAqx4xG64xv F2IEw4CE5I8CrVC2j2WlYx0E2Ix0cI8IcVAFwI0_Jr0_Jr4lYx0Ex4A2jsIE14v26r1j6r 4UMcvjeVCFs4IE7xkEbVWUJVW8JwACjcxG0xvEwIxGrwCY1x0262kKe7AKxVWUAVWUtwCF 04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02F40E14v26r1j6r 18MI8I3I0E7480Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_JF0_Jw1lIxkGc2Ij64vI r41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7CjxVAFwI0_Jr0_Gr 1lIxAIcVCF04k26cxKx2IYs7xG6r1j6r1xMIIF0xvEx4A2jsIE14v26r1j6r4UMIIF0xvE x4A2jsIEc7CjxVAFwI0_Gr0_Gr1UYxBIdaVFxhVjvjDU0xZFpf9x07bYYLPUUUUU= X-CM-SenderInfo: x2kh0wp0lqwv3d6l2u1dvotugofq/ =E5=9C=A8 2026-02-25=E4=B8=89=E7=9A=84 08:26 +0100=EF=BC=8CThomas Zimmerman= n=E5=86=99=E9=81=93=EF=BC=9A > Hi, >=20 > Am 25.02.26 um 07:13 schrieb Icenowy Zheng: > > The ioctl interfaces for dumb buffers currently only properly > > support > > linear buffers. > >=20 > > Mention this in the documentation snippet of dumb-buffers source > > code, > > which is referenced by drm-kms.rst and will end up in the built > > kernel > > documentation. > >=20 > > Also mention the existence of current drivers abusing dumb buffers > > for > > AFBC to reduce confusion about this. > >=20 > > Signed-off-by: Icenowy Zheng > > --- > > =C2=A0 drivers/gpu/drm/drm_dumb_buffers.c | 7 ++++++- >=20 > We documented the meaning of the color bits and the behavior of the=20 > dumb-buffer interface at [1]. If anything is missing, it should be > added=20 > there. Yes, I saw this piece of document; however it's part of the interface document instead of a concept document, and the whole existence of the document snippet I am changing can be considered a duplicate of the interface document. Thanks Icenowy >=20 > Best regards > Thomas >=20 > [1]=20 > https://elixir.bootlin.com/linux/v6.19/source/include/uapi/drm/drm_mode.h= #L1200 >=20 > > =C2=A0 1 file changed, 6 insertions(+), 1 deletion(-) > >=20 > > diff --git a/drivers/gpu/drm/drm_dumb_buffers.c > > b/drivers/gpu/drm/drm_dumb_buffers.c > > index e2b62e5fb891b..06f74460adf62 100644 > > --- a/drivers/gpu/drm/drm_dumb_buffers.c > > +++ b/drivers/gpu/drm/drm_dumb_buffers.c > > @@ -57,7 +57,12 @@ > > =C2=A0=C2=A0 * > > =C2=A0=C2=A0 * Note that dumb objects may not be used for gpu accelerat= ion, > > as has been > > =C2=A0=C2=A0 * attempted on some ARM embedded platforms. Such drivers r= eally > > must have > > - * a hardware-specific ioctl to allocate suitable buffer objects. > > + * a hardware-specific ioctl to allocate suitable buffer objects. > > They are > > + * also currently meant for only linear buffers, and using them > > with any > > + * modifier other than DRM_FORMAT_MOD_LINEAR is undefined > > behavior. There > > + * exist some KMS drivers abusing dumb objects for AFBC > > framebuffers, but this > > + * behavior is discouraged, only exists as a hack now and > > shouldn't be > > + * replicated. > > =C2=A0=C2=A0 */ > > =C2=A0=20 > > =C2=A0 static int drm_mode_align_dumb(struct drm_mode_create_dumb *args= ,