[PATCH v2] drm/panfrost: Document base field location constraint in panfrost_gem_object

From: Boris Brezillon <boris.brezillon@collabora.com>
To: Rob Herring <robh+dt@kernel.org>,
	Tomeu Vizoso <tomeu@tomeuvizoso.net>,
	Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>,
	Steven Price <steven.price@arm.com>
Cc: Boris Brezillon <boris.brezillon@collabora.com>,
	dri-devel@lists.freedesktop.org
Subject: [PATCH v2] drm/panfrost: Document base field location constraint in panfrost_gem_object
Date: Fri, 29 Nov 2019 14:56:14 +0100	[thread overview]
Message-ID: <20191129135614.2439058-1-boris.brezillon@collabora.com> (raw)

I've spent hours chasing a memory corruption that was caused by
insertion of an extra field field before ->base. Let's document the
fact that base has to be the first field in panfrost_gem_object.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
---
Changes in v2:
* Use the proper prefix in the subject line
---
 drivers/gpu/drm/panfrost/panfrost_gem.h | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/gpu/drm/panfrost/panfrost_gem.h b/drivers/gpu/drm/panfrost/panfrost_gem.h
index b3517ff9630c..d480261fc177 100644
--- a/drivers/gpu/drm/panfrost/panfrost_gem.h
+++ b/drivers/gpu/drm/panfrost/panfrost_gem.h
@@ -10,6 +10,10 @@
 struct panfrost_mmu;
 
 struct panfrost_gem_object {
+	/*
+	 * Must be the first element because we're using some of the
+	 * drm_gem_shmem helpers.
+	 */
 	struct drm_gem_shmem_object base;
 	struct sg_table *sgts;
 
-- 
2.23.0

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