From nobody Sat Feb 7 19:41:09 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 65C1F2F25F9 for ; Mon, 12 Jan 2026 15:29:03 +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=1768231747; cv=none; b=CR+hLFR+4bobRcc7Eb4tHPGN3cQPxK1oj8Mpu6C7hBUWFHNHnRh149TRZ0S7GA0AbkI1YDBI527hwKWzxFq7qCWqJdaFKJKUZcIlE5LTBfhh4EITAsdTFU35stX0uNDbK3okTocyQuy4yf0BTnIU6LbN7Uzlx6iWZyE97MiFuTo= ARC-Message-Signature: i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1768231747; c=relaxed/simple; bh=2EBOUlFdg3MszkEBGNlnfrYy2xczDbjzxVzmkBS+tt8=; h=From:To:Cc:Subject:Date:Message-Id:In-Reply-To:References: MIME-Version; b=D8r8n0keA5UVY4AZQ0kS9hpM6I0MxPsbG+NzM3gbTmNjifiHZczDPdVcD0RkxSxJ8OxKIRrBjVJgVu8PO8959SPOwGnwwSmFFTP9GODUbK0+ntkrVXBJqiqjT7FidT2fLi/FNerHBUvVUPs/RGwCb+Gw2lXk0gc9oJJyurggY00= 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=lpg9efCT; 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="lpg9efCT" DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=collabora.com; s=mail; t=1768231741; bh=2EBOUlFdg3MszkEBGNlnfrYy2xczDbjzxVzmkBS+tt8=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=lpg9efCTjL9dEcFCNwqHaMJbX0lZhj+F9+dNTVXtFuT1nb0YzDRn8IIa2LqU85lwE xcZ/fg/UcpNjWs/DHM3prQFyQhpdYwLVYpKUDpHWgzAKBZwVMsGtNS2e+PbXBtokI8 GQtKXxQVh+/TYoAPM2+/Z/bT44afLkB0rtdDLDqYmhDhHII93Ttpv2tuCWZp07UNPm xVHKS+BGltaLFfs1JEu/qxmkW9zchhWn6lokjh67RixNh8nfqabSH0TYWzvj/pf3rP UZsgc2E36Hy6SMcv0ypJjNGAVn84pZVmtWGvyrRabqA/ucQyG10LHYqF1e3FTjr1k5 SpxLSw9a9vhAw== 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 E938917E13F1; Mon, 12 Jan 2026 16:29:00 +0100 (CET) From: Vivek Das Mohapatra To: superm1@kernel.org Cc: airlied@gmail.com, alexander.deucher@amd.com, amd-gfx@lists.freedesktop.org, christian.koenig@amd.com, dri-devel@lists.freedesktop.org, harry.wentland@amd.com, kernel@collabora.com, linux-kernel@vger.kernel.org, simona@ffwll.ch, siqueira@igalia.com, sunpeng.li@amd.com, vivek@collabora.com Subject: [PATCH v2] drm/amd/display: Initialise backlight level values from hw Date: Mon, 12 Jan 2026 15:28:56 +0000 Message-Id: <20260112152856.2616532-1-vivek@collabora.com> X-Mailer: git-send-email 2.39.5 In-Reply-To: <7ec7b4ae-6186-4961-a857-f97afcfc3ded@kernel.org> References: <7ec7b4ae-6186-4961-a857-f97afcfc3ded@kernel.org> 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 Reviewed-by: Mario Limonciello (AMD) --- .../gpu/drm/amd/display/amdgpu_dm/amdgpu_dm.c | 18 +++++++++++++++++- 1 file changed, 17 insertions(+), 1 deletion(-) 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..9e8cbfeee915 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; @@ -5300,8 +5304,20 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm= _connector *aconnector) 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; - } else + } else { + /* + * 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; + } drm_dbg_driver(drm, "DM: Registered Backlight device: %s\n", bl_name); + } } =20 static int initialize_plane(struct amdgpu_display_manager *dm, --=20 2.39.5