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b=r/c1iNrNvxIBECjyOzeIaVKSUQ5Ez9PxYO9fyLGq24VBmJYSB9R/IwJbxovNNV0iA34zQ99/oL6MbSSw0H/WXKoR4/X3aT1aQWsGC1aqz0EK4v4SV6rmZQQqCUnCqvjxBO8fXYp3N3+5hvSIHXQ6hR/X6fKMjHqPUJhswuR4gtk= Authentication-Results: dkim=none (message not signed) header.d=none;dmarc=none action=none header.from=amd.com; Received: from PH8PR12MB6914.namprd12.prod.outlook.com (2603:10b6:510:1cb::21) by DM4PR12MB7767.namprd12.prod.outlook.com (2603:10b6:8:100::16) with Microsoft SMTP Server (version=TLS1_2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id 15.21.315.12; Thu, 13 Aug 2026 17:45:35 +0000 Received: from PH8PR12MB6914.namprd12.prod.outlook.com ([fe80::2893:177a:72b0:6000]) by PH8PR12MB6914.namprd12.prod.outlook.com ([fe80::2893:177a:72b0:6000%7]) with mapi id 15.21.0315.012; Thu, 13 Aug 2026 17:45:35 +0000 Message-ID: <20f0d0e6-c551-4982-9820-68169039e504@amd.com> Date: Thu, 13 Aug 2026 12:45:31 -0500 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH] drm/amd/display: Scale custom brightness curve from full range Content-Language: en-US To: Akhmed Zhitaev , 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, alex.hung@amd.com, roman.li@amd.com, stable@vger.kernel.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org References: <20260813170959.22073-1-zhitaevakh@gmail.com> From: Mario Limonciello In-Reply-To: <20260813170959.22073-1-zhitaevakh@gmail.com> Content-Type: text/plain; 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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; > Is this still needed with "drm/amd/display: Fix backlight max_brightness to match exported range" https://github.com/torvalds/linux/commit/f1b5d8f9cc54ae8a2567ac126867ae488e1bf625