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Date:   Tue,  8 Jun 2021 14:32:38 +1000
Message-Id: <20210608143159.1.I230026301243fbcee23d408c75aa468c1fec58f7@changeid>
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Subject: [PATCH] drm/amd/display: Fix error code on failure to set brightness
From:   Anand K Mistry <amistry@google.com>
To:     amd-gfx@lists.freedesktop.org
Cc:     Anand K Mistry <amistry@google.com>,
        Alex Deucher <alexander.deucher@amd.com>,
        Aurabindo Pillai <aurabindo.pillai@amd.com>,
        Bas Nieuwenhuizen <bas@basnieuwenhuizen.nl>,
        "=?UTF-8?q?Christian=20K=C3=B6nig?=" <christian.koenig@amd.com>,
        Daniel Vetter <daniel@ffwll.ch>,
        David Airlie <airlied@linux.ie>, Eryk Brol <eryk.brol@amd.com>,
        Harry Wentland <harry.wentland@amd.com>,
        Leo Li <sunpeng.li@amd.com>,
        Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>,
        Nikola Cornij <nikola.cornij@amd.com>,
        Qingqing Zhuo <qingqing.zhuo@amd.com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>,
        Wayne Lin <Wayne.Lin@amd.com>, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
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Precedence: bulk

The backlight_ops.update_status function is required to return a
negative error code on failure. Returning a positive code may be
interpreted as a success. This is true for the 'brightness' sysfs file,
which passes through a non-zero value as the return value of the write()
syscall. This is interpreted in user-space as a successful write of 1
character, which is obviously wrong.

It's not clear exactly what error code to use, but EINVAL should be
reasonable.

Signed-off-by: Anand K Mistry <amistry@google.com>
---

 drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
index 652cc1a0e450..ad322613390d 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c
@@ -3431,7 +3431,7 @@ static int amdgpu_dm_backlight_update_status(struct backlight_device *bd)
 	else
 		rc = dc_link_set_backlight_level(dm->backlight_link, brightness, 0);
 
-	return rc ? 0 : 1;
+	return rc ? 0 : -EINVAL;
 }
 
 static int amdgpu_dm_backlight_get_brightness(struct backlight_device *bd)
-- 
2.32.0.rc1.229.g3e70b5a671-goog