From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-alma10-1.taild15c8.ts.net [100.103.45.18]) (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 3E06B403AE0; Wed, 12 Aug 2026 22:21:47 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=100.103.45.18 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786573309; cv=none; b=AY2WZavSvM+BOcv2HvYdAmHhpmEe5/ijoKt+LmuNRq4K0zf7P510zfNtuOWrfWmiJz4MXCq/NB/CiNPHZ5eU62XP+WYEp8FIo5LGpWQ1jLDMbvadhhEWKSnKW3THIuMUBOacFsW+74hsWEHibWGtlZMknkB+Gd4vOmg9DQeE9IQ= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1786573309; c=relaxed/simple; bh=EsfG38HkJbkAV/VN4qU3q9SxTzbrIxMHdzU8kvW0EpE=; h=Date:From:To:Cc:Subject:Message-ID:References:MIME-Version: Content-Type:Content-Disposition:In-Reply-To; b=ldvX9dva8XyoAgXuCB1ymI32LoOS47mTrR/xDHe527VxZbbTZo1Z9SJHnzMb6fujdMQNfmMghub1+lPX35NAGFpEUlND8P5pfMAVqZHDyqFLGZc55XyloDIA4nILmVrSPSSe8Sxy/nNrE8SHp7uPqOSUoJf5d69wTH7zp66I8Gw= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=WyzytDJL; arc=none smtp.client-ip=100.103.45.18 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="WyzytDJL" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 772CB1F000E9; Wed, 12 Aug 2026 22:21:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1786573307; bh=lSjfsT9lz56s5Gpwb7v0lw3+r8UguBFDrjycJYrRh50=; h=Date:From:To:Cc:Subject:References:In-Reply-To; b=WyzytDJLW4uygTB8IkrNv+M6l8KIdEXdWj0ar5ta618faApIAlLlo6conCSs2Vnf8 /RmPyIQchw5ZRaEgcfwzoN/asl/qrvGpDYC/EmT6+MHkCHruoug94FEa/9ERu3Tgjf UMARMLQSCJAPLr8J7MLgeiQLTOt2EDgshkBHbbERI6funv0ohrjMmthWR2NUqikhoo 7m4S7acpeOBGRgcHuOKdlx03xQoh6bAiZbpXi/7YThGLbExImYG6uoIVY+Ym57rzmL zCxtonGW2KVyLbyH3TxflcIV4spiCqk96HrQTfYz0p1zPjZgH/WWjAriS6804MHqgx PwklUDbDxCZrg== Date: Wed, 12 Aug 2026 18:21:46 -0400 From: Sasha Levin To: Alex Deucher Cc: Sergio Callegari , Greg KH , Thorsten Leemhuis , stable@vger.kernel.org, Mario Limonciello , Alex Deucher , Linux kernel regressions list , "amd-gfx@lists.freedesktop.org" , Christian =?iso-8859-1?Q?K=F6nig?= , George Zhang Subject: Re: [REGRESSION] Please revert 1191285ecb42 from 7.1.y Message-ID: References: <9c6acb62-4080-48e6-9ba2-d1c457c4ec88@gmail.com> <2026081106-pebbly-cahoots-37a7@gregkh> <23db5f95-c2d6-4712-856e-28f647e184f7@leemhuis.info> <1caea72e-b9c8-452b-a3ff-5690d948b4fc@gmail.com> <2026081151-reabsorb-calamari-7442@gregkh> <8a0fad2d-788a-403f-a880-2f97c6708275@gmail.com> Precedence: bulk X-Mailing-List: stable@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: On Tue, Aug 11, 2026 at 01:25:14PM -0400, Alex Deucher wrote: >On Tue, Aug 11, 2026 at 11:25 AM Sergio Callegari > wrote: >> >> On 11/08/2026 10:08, Greg KH wrote: >> > We aim to be "bug compatible" with Linus's branch, otherwise the >> > "pressure" to fix those bugs goes down. But I defer to the maintainers >> > of the code involved if it is being worked on, and they want it >> > reverted, great, we can do that. Otherwise we prefer to leave it as-is. >> >> I understand. Sorry for asking about things that might be obvious to >> most people here. My expectation was that only a selected subset of the >> patches on the Linus' tree were to enter in stable, so do we really need >> to have stable "bug compatible" wrt this bug? The original behavior was >> not free of issues, but they were rather minor (a reporting issue). Now >> we have this very bad behavior where the display remains dark. >> >> To make the matter worse, on systems that have encrypted root the screen >> remains dark also on that password prompt (observed with plymouth). >> >> In any case, I managed testing 7.2.0RC7 and it is fine again. >> >> Looks like the Linus' tree has more changes wrt backlight, and the >> interesting ones are probably those in the cumulative fix >> https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=973fd9493ec21f12e760fbbedeb7b0b2317c02f4. >> > >Thanks for testing. It sounds like we should revert the change from >stable. There must be some dependency we are missing in stable. Hmm... In stable kernels, convert_custom_brightness() still scales the user value by (max - min), but f1b5d8f9cc54 ("drm/amd/display: Fix backlight max_brightness to match exported range") widened the exported range to max. Past ~(max - min), scale_input_to_fw() exceeds AMDGPU_MAX_BL_LEVEL and convert_brightness_from_user() returns >0xFFFF, which wraps in dce_driver_set_backlight(). With the defaults the cliff lands on 64533, which is what Sergio sees. Upstream only hides it: mod_power_set_backlight_percent() clamps at 100%. Does this make sense? -- Thanks, Sasha