From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 765D4E9B25A for ; Wed, 25 Feb 2026 06:13:47 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id E83EA10E6AD; Wed, 25 Feb 2026 06:13:46 +0000 (UTC) Received: from cstnet.cn (smtp25.cstnet.cn [159.226.251.25]) by gabe.freedesktop.org (Postfix) with ESMTPS id E2F3C10E6AD for ; Wed, 25 Feb 2026 06:13:45 +0000 (UTC) Received: from edelgard.fodlan.icenowy.me (unknown [112.94.100.4]) by APP-05 (Coremail) with SMTP id zQCowACHGw8Rk55pRrIcCQ--.9682S2; Wed, 25 Feb 2026 14:13:38 +0800 (CST) From: Icenowy Zheng To: Maarten Lankhorst , Maxime Ripard , Thomas Zimmermann , David Airlie , Simona Vetter Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Icenowy Zheng Subject: [PATCH] drm/dumb-buffers: document that it's only for linear FB Date: Wed, 25 Feb 2026 14:13:15 +0800 Message-ID: <20260225061315.1003811-1-zhengxingda@iscas.ac.cn> X-Mailer: git-send-email 2.52.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit X-CM-TRANSID: zQCowACHGw8Rk55pRrIcCQ--.9682S2 X-Coremail-Antispam: 1UD129KBjvJXoW7Cr1xWr4xtF1UuF15Kw4rKrg_yoW8XryxpF 4fKrWjvrnrJa93tr1DCFn8WFy5Aa9rXFWrGayvyw1fZF1qyF12gFn5t3yYqF9rJrn7XFy0 qr9FyryruryjyrJanT9S1TB71UUUUU7qnTZGkaVYY2UrUUUUjbIjqfuFe4nvWSU5nxnvy2 9KBjDU0xBIdaVrnRJUUUkl14x267AKxVW8JVW5JwAFc2x0x2IEx4CE42xK8VAvwI8IcIk0 rVWrJVCq3wAFIxvE14AKwVWUJVWUGwA2ocxC64kIII0Yj41l84x0c7CEw4AK67xGY2AK02 1l84ACjcxK6xIIjxv20xvE14v26r4j6ryUM28EF7xvwVC0I7IYx2IY6xkF7I0E14v26r4j 6F4UM28EF7xvwVC2z280aVAFwI0_Cr1j6rxdM28EF7xvwVC2z280aVCY1x0267AKxVW0oV Cq3wAS0I0E0xvYzxvE52x082IY62kv0487Mc02F40EFcxC0VAKzVAqx4xG6I80ewAv7VC0 I7IYx2IY67AKxVWUJVWUGwAv7VC2z280aVAFwI0_Jr0_Gr1lOx8S6xCaFVCjc4AY6r1j6r 4UM4x0Y48IcxkI7VAKI48JM4x0x7Aq67IIx4CEVc8vx2IErcIFxwCY1x0262kKe7AKxVWU AVWUtwCF04k20xvY0x0EwIxGrwCFx2IqxVCFs4IE7xkEbVWUJVW8JwC20s026c02F40E14 v26r1j6r18MI8I3I0E7480Y4vE14v26r106r1rMI8E67AF67kF1VAFwI0_Jw0_GFylIxkG c2Ij64vIr41lIxAIcVC0I7IYx2IY67AKxVWUJVWUCwCI42IY6xIIjxv20xvEc7CjxVAFwI 0_Jr0_Gr1lIxAIcVCF04k26cxKx2IYs7xG6r1j6r1xMIIF0xvEx4A2jsIE14v26r1j6r4U MIIF0xvEx4A2jsIEc7CjxVAFwI0_Jr0_GrUvcSsGvfC2KfnxnUUI43ZEXa7VUbSfO7UUUU U== X-Originating-IP: [112.94.100.4] X-CM-SenderInfo: x2kh0wp0lqwv3d6l2u1dvotugofq/ X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" The ioctl interfaces for dumb buffers currently only properly support linear buffers. 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. Also mention the existence of current drivers abusing dumb buffers for AFBC to reduce confusion about this. Signed-off-by: Icenowy Zheng --- drivers/gpu/drm/drm_dumb_buffers.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-) 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 @@ * * Note that dumb objects may not be used for gpu acceleration, as has been * attempted on some ARM embedded platforms. Such drivers really 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. */ static int drm_mode_align_dumb(struct drm_mode_create_dumb *args, -- 2.52.0