From nobody Sat Feb 7 23:47:51 2026 Received: from bali.collaboradmins.com (bali.collaboradmins.com [148.251.105.195]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id E87181E4AF for ; Mon, 12 Jan 2026 12:21:50 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=148.251.105.195 ARC-Seal: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768220512; cv=none; b=dkCL/YbbZ+GsEkH6015RU7MtnppRoaLgniJMIHygFCOOI5NgzjxKbIfZTQ/hswOrB9VV9i2mVJjzG0UqdKZ/BXobEnKMjrl9/u8hxAdveQA2c30WcXQiEQp5UK3vT9/4SLmtu61XrCs6sUqMnq7U3gG+MPSq9B8DUpVJH3glD3g= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768220512; c=relaxed/simple; bh=iRtfMCL1Oz7vI19NsR0rJtTifPlnDjelAukBq66MZrY=; h=From:To:Cc:Subject:Date:Message-Id:MIME-Version; b=b6av4nZiOHzUR7u5d497/nqOlfZDa1GIOmaKRzxgB6rspH27LAjn7hvH6C7pxT1Ipzg1888KRSxEsJg5RvfGBE1uPI7fwvi3WUhTa4Afc1itPoPPv+j/IxIqfo3iyf/Ybw1DUrnRKgcVCNT6eXeU/2ONeI+IzRowBiGZBJSY+n8= ARC-Authentication-Results: i=1; smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com; spf=pass smtp.mailfrom=collabora.com; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b=kchJVSnv; arc=none smtp.client-ip=148.251.105.195 Authentication-Results: smtp.subspace.kernel.org; dmarc=pass (p=none dis=none) header.from=collabora.com Authentication-Results: smtp.subspace.kernel.org; spf=pass smtp.mailfrom=collabora.com Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=collabora.com header.i=@collabora.com header.b="kchJVSnv" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1768220508; bh=iRtfMCL1Oz7vI19NsR0rJtTifPlnDjelAukBq66MZrY=; h=From:To:Cc:Subject:Date:From; b=kchJVSnvf8Az4kLIN6nwQlaUO8oCVTJpDz4fZ4UDRsQBeSmTzhl21q03BUIJ0CX6g 9RcJfsPZmCXJt0HFDXbvuvutBP6b6xFyP8iac/HL3xvmtmtDasDMZ5GjN3WWEFs+F+ +YTLYQDyT36wTdTYrsN4xTVPUFSModSOqG785KHBtI0TjimxwsjdnGDjb/urPtAwAo mMV4lwGofzWnbbQXp5+eCbCwExWaAHkwt8HXrCHtoJ8zDbziXqewk4+bcjimynu9nL A1fxt9ebjRuqjkpiOapCg0NV7CO+RgdULoYEoStd/A276z4En2o9GuLgFkkjDgllT8 EtrYL421nak3Q== Received: from nemo.lan (unknown [IPv6:2a07:244:40:6b00::646]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange X25519 server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) (Authenticated sender: vivek) by bali.collaboradmins.com (Postfix) with ESMTPSA id 6673D17E0CB0; Mon, 12 Jan 2026 13:21:48 +0100 (CET) From: Vivek Das Mohapatra To: Harry Wentland , Leo Li , Rodrigo Siqueira , Alex Deucher , =?UTF-8?q?Christian=20K=C3=B6nig?= , David Airlie , Simona Vetter Cc: kernel@collabora.com, amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org Subject: [PATCH v1] drm/amd/display: Initialise backlight level values from hw Date: Mon, 12 Jan 2026 12:20:46 +0000 Message-Id: <20260112122140.2609679-1-vivek@collabora.com> X-Mailer: git-send-email 2.39.5 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" Internal backlight levels are initialised from ACPI but the values are sometimes out of sync with the levels in effect until there has been a read from hardware (eg triggered by reading from sysfs). This means that the first drm_commit can cause the levels to be set to a different value than the actual starting one, which results in a sudden change in brightness. This path shows the problem (when the values are out of sync): amdgpu_dm_atomic_commit_tail() -> amdgpu_dm_commit_streams() -> amdgpu_dm_backlight_set_level(..., dm->brightness[n]) This patch calls the backlight ops get_brightness explicitly at the end of backlight registration to make sure dm->brightness[n] is in sync with the actual hardware levels. Signed-off-by: Vivek Das Mohapatra --- .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 16 ++++++++++++++++ 1 file changed, 16 insertions(+) diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c b/drivers/gp= u/drm/amd/display/amdgpu_dm/amdgpu_dm.c index 354e359c4507..50f0547ed63c 100644 --- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c +++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c @@ -5258,6 +5258,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_= connector *aconnector) struct amdgpu_dm_backlight_caps *caps; char bl_name[16]; int min, max; + int real_brightness; + int init_brightness; =20 if (aconnector->bl_idx =3D=3D -1) return; @@ -5282,6 +5284,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_= connector *aconnector) } else props.brightness =3D props.max_brightness =3D MAX_BACKLIGHT_LEVEL; =20 + init_brightness =3D props.brightness; + if (caps->data_points && !(amdgpu_dc_debug_mask & DC_DISABLE_CUSTOM_BRIGH= TNESS_CURVE)) { drm_info(drm, "Using custom brightness curve\n"); props.scale =3D BACKLIGHT_SCALE_NON_LINEAR; @@ -5297,6 +5301,18 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm= _connector *aconnector) &amdgpu_dm_backlight_ops, &props); dm->brightness[aconnector->bl_idx] =3D props.brightness; =20 + /* + * dm->brightness[x] can be inconsistent just after startup until + * ops.get_brightness is called. + */ + real_brightness =3D + amdgpu_dm_backlight_ops.get_brightness(dm->backlight_dev[aconnector->bl_= idx]); + + if (real_brightness !=3D init_brightness) { + dm->actual_brightness[aconnector->bl_idx] =3D real_brightness; + dm->brightness[aconnector->bl_idx] =3D real_brightness; + } + if (IS_ERR(dm->backlight_dev[aconnector->bl_idx])) { drm_err(drm, "DM: Backlight registration failed!\n"); dm->backlight_dev[aconnector->bl_idx] =3D NULL; --=20 2.39.5