linux-kernel - [PATCH] drm/sti: Avoid full proxy f

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Date:   Wed, 11 Jan 2023 01:50:06 +0530
From:   Deepak R Varma <drv@...lo.com>
To:     Alain Volmat <alain.volmat@...s.st.com>,
        David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>,
        dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Cc:     Saurabh Singh Sengar <ssengar@...rosoft.com>,
        Praveen Kumar <kumarpraveen@...ux.microsoft.com>
Subject: [PATCH] drm/sti: Avoid full proxy f_ops for sti debug attributes

Using DEFINE_SIMPLE_ATTRIBUTE macro with the debugfs_create_file()
function adds the overhead of introducing a proxy file operation
functions to wrap the original read/write inside file removal protection
functions. This adds significant overhead in terms of introducing and
managing the proxy factory file operations structure and function
wrapping at runtime.
As a replacement, a combination of DEFINE_DEBUGFS_ATTRIBUTE macro paired
with debugfs_create_file_unsafe() is suggested to be used instead.  The
DEFINE_DEBUGFS_ATTRIBUTE utilises debugfs_file_get() and
debugfs_file_put() wrappers to protect the original read and write
function calls for the debug attributes. There is no need for any
runtime proxy file operations to be managed by the debugfs core.
Following coccicheck make command helped identify this change:

make coccicheck M=drivers/gpu/drm/i915/ MODE=patch COCCI=./scripts/coccinelle/api/debugfs/debugfs_simple_attr.cocci

Signed-off-by: Deepak R Varma <drv@...lo.com>
---
Note: Change cross compile tested using stm32_defconfig for arm

 drivers/gpu/drm/sti/sti_drv.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/gpu/drm/sti/sti_drv.c b/drivers/gpu/drm/sti/sti_drv.c
index ef6a4e63198f..c9be82043638 100644
--- a/drivers/gpu/drm/sti/sti_drv.c
+++ b/drivers/gpu/drm/sti/sti_drv.c
@@ -67,8 +67,8 @@ static int sti_drm_fps_set(void *data, u64 val)
 	return 0;
 }

-DEFINE_SIMPLE_ATTRIBUTE(sti_drm_fps_fops,
-			sti_drm_fps_get, sti_drm_fps_set, "%llu\n");
+DEFINE_DEBUGFS_ATTRIBUTE(sti_drm_fps_fops,
+			 sti_drm_fps_get, sti_drm_fps_set, "%llu\n");

 static int sti_drm_fps_dbg_show(struct seq_file *s, void *data)
 {
@@ -97,8 +97,8 @@ static void sti_drm_dbg_init(struct drm_minor *minor)
 				 ARRAY_SIZE(sti_drm_dbg_list),
 				 minor->debugfs_root, minor);

-	debugfs_create_file("fps_show", S_IRUGO | S_IWUSR, minor->debugfs_root,
-			    minor->dev, &sti_drm_fps_fops);
+	debugfs_create_file_unsafe("fps_show", S_IRUGO | S_IWUSR, minor->debugfs_root,
+				   minor->dev, &sti_drm_fps_fops);

 	DRM_INFO("%s: debugfs installed\n", DRIVER_NAME);
 }
-- 
2.34.1