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Thu, 13 Aug 2026 10:10:24 -0700 (PDT) Received: from cachyos-x8664 ([77.83.245.95]) by smtp.gmail.com with ESMTPSA id 5b1f17b1804b1-49981b0f6b1sm76662355e9.4.2026.08.13.10.10.20 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 13 Aug 2026 10:10:24 -0700 (PDT) From: Akhmed Zhitaev To: amd-gfx@lists.freedesktop.org Cc: harry.wentland@amd.com, sunpeng.li@amd.com, siqueira@igalia.com, alexander.deucher@amd.com, christian.koenig@amd.com, airlied@gmail.com, simona@ffwll.ch, mario.limonciello@amd.com, alex.hung@amd.com, roman.li@amd.com, stable@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org, Akhmed Zhitaev Subject: [PATCH] drm/amd/display: Scale custom brightness curve from full range Date: Thu, 13 Aug 2026 22:09:59 +0500 Message-ID: <20260813170959.22073-1-zhitaevakh@gmail.com> X-Mailer: git-send-email 2.55.0 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Custom brightness curves use an 8-bit input signal. After exporting the full PWM range to userspace, the curve normalizer still divides requests by the physical PWM span. On panels with a nonzero minimum PWM level, this can produce a curve input greater than 255 and send an invalid backlight level to DC. Scale the userspace [0..max] range to the curve's [0..255] range instead. This retains the full advertised range and keeps the reverse readback conversion unchanged. Fixes: 8dbd72cb7900 ("drm/amd/display: Export full brightness range to userspace") Cc: stable@vger.kernel.org Signed-off-by: Akhmed Zhitaev --- drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) 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 40d82a3ee..533c69f0b 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -5131,10 +5131,10 @@ static int get_brightness_range(const struct amdgpu_dm_backlight_caps *caps, return 1; } -/* Rescale from [min..max] to [0..AMDGPU_MAX_BL_LEVEL] */ -static inline u32 scale_input_to_fw(int min, int max, u64 input) +/* Rescale userspace [0..max] to the firmware curve's [0..255]. */ +static inline u32 scale_input_to_fw(int max, u64 input) { - return DIV_ROUND_CLOSEST_ULL(input * AMDGPU_MAX_BL_LEVEL, max - min); + return DIV_ROUND_CLOSEST_ULL(input * AMDGPU_MAX_BL_LEVEL, max); } /* Rescale from [0..AMDGPU_MAX_BL_LEVEL] to [min..max] */ @@ -5147,7 +5147,7 @@ static void convert_custom_brightness(const struct amdgpu_dm_backlight_caps *cap unsigned int min, unsigned int max, uint32_t *user_brightness) { - u32 brightness = scale_input_to_fw(min, max, *user_brightness); + u32 brightness = scale_input_to_fw(max, *user_brightness); u8 lower_signal, upper_signal, upper_lum, lower_lum, lum; int left, right; -- 2.55.0