From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org Received: from gabe.freedesktop.org (gabe.freedesktop.org [131.252.210.177]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.lore.kernel.org (Postfix) with ESMTPS id 81BFFC9EC90 for ; Mon, 12 Jan 2026 14:10:35 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id EFD6210E3DF; Mon, 12 Jan 2026 14:10:34 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="KjrDl3j+"; dkim-atps=neutral Received: from sea.source.kernel.org (sea.source.kernel.org [172.234.252.31]) by gabe.freedesktop.org (Postfix) with ESMTPS id DFD2410E3DE; Mon, 12 Jan 2026 14:10:33 +0000 (UTC) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by sea.source.kernel.org (Postfix) with ESMTP id 6EAC842AFD; Mon, 12 Jan 2026 14:10:33 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 7771EC16AAE; Mon, 12 Jan 2026 14:10:32 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1768227033; bh=CfNJPE1nl/7o5k/wDQ4X6fS/hd3zNOqhNxuVfUQZkxU=; h=Date:Subject:To:Cc:References:From:In-Reply-To:From; b=KjrDl3j+2AfjB9/eZ36YStEGgwjSiXVe0+Pb69beUBaY10cZ2oknCPZw45Rps7xOa kJjjWD4HPlHmXqKBtSM+nzIF2xjYyDo0nccIJ1c1tuRaiDadE9PljcA9NRhizaO0Ib HNTimgli+moD6ttdkwJuNE7EGywiKVSTUMx/pMonxrpKTQ75JclWcKGeQjM1xjZy3s 7j/j+A7BcEs+vquxLe3TaR+6kLBHcmovCnDptlyTyeNKU7nWJpGqNioIPTDmcbwwy4 7mZPC+1joDR4FJgJAxWPFeNSrB3UaXbSilhEnG6joK0CqB6QDDpabAZ+0Wuoa1q/vf cA+5sV4NLLSyQ== Message-ID: <7ec7b4ae-6186-4961-a857-f97afcfc3ded@kernel.org> Date: Mon, 12 Jan 2026 08:10:31 -0600 MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [PATCH v1] drm/amd/display: Initialise backlight level values from hw To: Vivek Das Mohapatra , Harry Wentland , Leo Li , Rodrigo Siqueira , Alex Deucher , =?UTF-8?Q?Christian_K=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 References: <20260112122140.2609679-1-vivek@collabora.com> Content-Language: en-US From: Mario Limonciello In-Reply-To: <20260112122140.2609679-1-vivek@collabora.com> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-BeenThere: amd-gfx@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Discussion list for AMD gfx List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: amd-gfx-bounces@lists.freedesktop.org Sender: "amd-gfx" On 1/12/26 6:20 AM, Vivek Das Mohapatra wrote: > 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 Thanks for the patch. One comment below. > --- > .../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/gpu/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; > > if (aconnector->bl_idx == -1) > return; > @@ -5282,6 +5284,8 @@ amdgpu_dm_register_backlight_device(struct amdgpu_dm_connector *aconnector) > } else > props.brightness = props.max_brightness = MAX_BACKLIGHT_LEVEL; > > + init_brightness = props.brightness; > + > if (caps->data_points && !(amdgpu_dc_debug_mask & DC_DISABLE_CUSTOM_BRIGHTNESS_CURVE)) { > drm_info(drm, "Using custom brightness curve\n"); > props.scale = 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] = props.brightness; > > + /* > + * dm->brightness[x] can be inconsistent just after startup until > + * ops.get_brightness is called. > + */ > + real_brightness = > + amdgpu_dm_backlight_ops.get_brightness(dm->backlight_dev[aconnector->bl_idx]); > + > + if (real_brightness != init_brightness) { > + dm->actual_brightness[aconnector->bl_idx] = real_brightness; > + dm->brightness[aconnector->bl_idx] = real_brightness; > + } > + I think this call should be after the IS_ERR() check right below it in only the case that IS_ERR() failed. > if (IS_ERR(dm->backlight_dev[aconnector->bl_idx])) { > drm_err(drm, "DM: Backlight registration failed!\n"); > dm->backlight_dev[aconnector->bl_idx] = NULL;