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[87.184.117.22]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-45d9e767d0bsm13548577f8f.3.2026.05.15.06.20.45 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Fri, 15 May 2026 06:20:45 -0700 (PDT) Message-ID: Date: Fri, 15 May 2026 15:20:44 +0200 Precedence: bulk X-Mailing-List: linux-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 User-Agent: Mozilla Thunderbird Subject: Re: [REGRESSION] bisected: 7.1rc1 breaks backlight control on Thinkpad T480 To: Thorsten Leemhuis Cc: Linux kernel regressions list , LKML , "Kandpal, Suraj" References: <233da598-4172-4f16-9fd5-67590984616a@leemhuis.info> From: Stefan Seyfried Content-Language: en-US In-Reply-To: <233da598-4172-4f16-9fd5-67590984616a@leemhuis.info> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Am 15.05.26 um 14:13 schrieb Thorsten Leemhuis: > On 5/15/26 13:47, Stefan Seyfried wrote: >> >> I found that 7.1rc1 broke the backlight control on my Thinkpad T480. >> Bisected it to >> >>> 40d2f5820951dee818d05c14677277048bd85f9f is the first bad commit >>> commit 40d2f5820951dee818d05c14677277048bd85f9f >>> Author: Suraj Kandpal >>> Date:   Tue Feb 24 08:43:22 2026 +0530 >>> >>>     drm/i915/backlight: Remove try_vesa_interface > > FWIW: Here are two bug reports that contain proposed fixes for what > might or might not be the issue your face: > > https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16043 > https://gitlab.freedesktop.org/drm/i915/kernel/-/work_items/16015 Thanks, will look into testing the patches floating around there. For now, this diff --git a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c index a8d56ebf06a2..c4ac46559669 100644 --- a/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c +++ b/drivers/gpu/drm/i915/display/intel_dp_aux_backlight.c @@ -745,7 +745,7 @@ int intel_dp_aux_init_backlight_funcs(struct intel_connector *connector) return 0; } - if (intel_dp_aux_supports_vesa_backlight(connector)) { + if (0 && intel_dp_aux_supports_vesa_backlight(connector)) { drm_dbg_kms(dev, "[CONNECTOR:%d:%s] Using VESA eDP backlight controls\n", connector->base.base.id, connector->base.name); panel->backlight.funcs = &intel_dp_vesa_bl_funcs; is enough to get the backlight control on the T480 going again. I know nothing about that code (obviously), but maybe "intel_dp_aux_supports_vesa_backlight()" is wrongly determining VESA backlight support on my machine? -- Stefan Seyfried "For a successful technology, reality must take precedence over public relations, for nature cannot be fooled." -- Richard Feynman