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 96B88C369BA for ; Tue, 15 Apr 2025 16:31:47 +0000 (UTC) Received: from gabe.freedesktop.org (localhost [127.0.0.1]) by gabe.freedesktop.org (Postfix) with ESMTP id 00BC710E054; Tue, 15 Apr 2025 16:31:47 +0000 (UTC) Authentication-Results: gabe.freedesktop.org; dkim=pass (2048-bit key; unprotected) header.d=kernel.org header.i=@kernel.org header.b="qok71dRj"; dkim-atps=neutral Received: from tor.source.kernel.org (tor.source.kernel.org [172.105.4.254]) by gabe.freedesktop.org (Postfix) with ESMTPS id E19A610E054 for ; Tue, 15 Apr 2025 16:31:44 +0000 (UTC) Received: from smtp.kernel.org (transwarp.subspace.kernel.org [100.75.92.58]) by tor.source.kernel.org (Postfix) with ESMTP id 8B4426115F; Tue, 15 Apr 2025 16:31:26 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 9C197C4CEEB; Tue, 15 Apr 2025 16:31:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1744734702; bh=4EdEafXnV/PDUOBNNdf12HctxlhvxP6Rqe4GpopzFoU=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=qok71dRjT30dka1KQAZwNSwrXM7xI+YGYnlgZfTOBTJbZs1iYH/LXNuo7HHlrGOBz U2TCnZG4OXLKxe5KiRIzUCNasymfIVmMa6p6w2lw4rtrfnZi3lHP880c13x2wstBcQ 7O++K+E5akDtWkfTmnVzVPoVrc6DTsSXO9ZKQZhns3O1nI5qSjhTtq1XRYyyHWCgpL jTJCayNINO761VL6B9kGANb1tIDo+gcXZSREQfQonn0PHVFQZ+WHIQk4ndShaJTIYM wNGIqA2NGqfdDBWEWx/XVant1ifEMmUxgsGB3efUSTvTjejpWdT+CMB4hRuU3v/flu x+x0Fl9hD7R/g== Date: Tue, 15 Apr 2025 17:31:37 +0100 From: Lee Jones To: Mario Limonciello Cc: mario.limonciello@amd.com, danielt@kernel.org, jingoohan1@gmail.com, Lennart Poettering , richard.purdie@linuxfoundation.org, dri-devel@lists.freedesktop.org Subject: Re: [PATCH] docs: backlight: Clarify `actual_brightness` Message-ID: <20250415163137.GB372032@google.com> References: <20250408192729.4091391-1-superm1@kernel.org> <20250415155319.GZ372032@google.com> <9663cf9b-6cb6-45b2-9e93-aaf73dec0155@kernel.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: <9663cf9b-6cb6-45b2-9e93-aaf73dec0155@kernel.org> X-BeenThere: dri-devel@lists.freedesktop.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Direct Rendering Infrastructure - Development List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: dri-devel-bounces@lists.freedesktop.org Sender: "dri-devel" On Tue, 15 Apr 2025, Mario Limonciello wrote: > On 4/15/2025 10:53 AM, Lee Jones wrote: > > On Tue, 08 Apr 2025, Mario Limonciello wrote: > > > > > From: Mario Limonciello > > > > > > Currently userspace software systemd treats `brightness` and > > > `actual_brightness` identically due to a bug found in an out of tree > > > driver. > > > > > > This however causes problems for in-tree drivers that use brightness > > > to report user requested `brightness` and `actual_brightness` to report > > > what the hardware actually has programmed. > > > > > > Clarify the documentation to match the behavior described in commit > > > 6ca017658b1f9 ("[PATCH] backlight: Backlight Class Improvements"). > > > > > > Cc: Lennart Poettering > > > Cc: richard.purdie@linuxfoundation.org > > > Link: https://github.com/systemd/systemd/pull/36881 > > > Signed-off-by: Mario Limonciello > > > --- > > > Documentation/ABI/stable/sysfs-class-backlight | 4 +++- > > > 1 file changed, 3 insertions(+), 1 deletion(-) > > > > > > diff --git a/Documentation/ABI/stable/sysfs-class-backlight b/Documentation/ABI/stable/sysfs-class-backlight > > > index 6102d6bebdf9a..909cacde85041 100644 > > > --- a/Documentation/ABI/stable/sysfs-class-backlight > > > +++ b/Documentation/ABI/stable/sysfs-class-backlight > > > @@ -26,7 +26,9 @@ Date: March 2006 > > > KernelVersion: 2.6.17 > > > Contact: Richard Purdie > > > Description: > > > - Show the actual brightness by querying the hardware. > > > + Show the actual brightness by querying the hardware. This > > > + takes into account other factors besides the value programmed > > > + for 'brightness' and may not match the value in 'brightness'. > > > > Which factors? Under what circumstances may the values not match? > > Is this question for your background or are you saying these should be > enumerated here in the documentation? Both. > Richard Purdie mentioned: > > "The challenge back then was that things like framebuffer blanking would > turn off the backlight but the single brightness attribute was implemented > inconsistently. Some drivers would report no backlight when blanking was > active, some would report the value stored in brightness. This had multiple > issues" > > For AMD the two cases that can cause this on amdgpu are Custom brightness > curves and Adaptive Backlight Management (ABM). Okay, that was for me. Please update the documentation. =:-) -- Lee Jones [李琼斯]