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 933CD3D7D97; Sat, 10 Oct 2026 11:41:10 +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=1791632471; cv=none; b=rH5SLSI/fRFQa/0h1htayPev4jF9wwmZVA291VyYHngLB2OtXibvPF845Uxr6Ihvo9tKgyNxDTJoHTRfiZ5GNI5QBEZ5S/loRVDbhE7+dgeuQfnB/Y9vpjWLZWxjBVLW3g0ZqjuAMBQ+hejiRfTVYVpyC0lLuKqTs6Yr02nU5MI= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1791632471; c=relaxed/simple; bh=ZYidxo02IVYvWFU8lpFRO4Ud7msb9FfXKfMIKHtb0EE=; h=Message-ID:Date:MIME-Version:Subject:To:Cc:References:From: In-Reply-To:Content-Type; b=psrf+q5PofoEWxXDMZohq0IQSCLTlug2ccSGYkgQSagzG5LMJlZX7/hVdE98pRaXM9aVa7AkJ18Rpwi+e15J1VlzqGVwbeZu6Cwg3B3SW4QMQY4tNVLfSpw5ot+rhpEI9tMlDUl+3eE3oSMtOW36czYAvOiZwyVz7Ttz406s6EA= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=ZkEv5zFU; 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="ZkEv5zFU" Received: by smtp.kernel.org (Postfix) with ESMTPSA id 88F131F000FF; Sat, 10 Oct 2026 11:41:08 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=kernel.org; s=k20260515; t=1791632470; bh=9SjSqb1bat/dMzzvu2mKqVLDhkDoigTG6FM2iaQiuTc=; h=Date:Subject:To:Cc:References:From:In-Reply-To; b=ZkEv5zFUodlYTzIPxYlhLNVZxaBuvWzPrk40lEHkXjq8QIe653OaWonsBuVm1KlS+ rSsGMO5YyvJzS8Ky57W9MwPUxWbMSi4Bf0Npc0QHVi+MKU+f4YAziMp41Rv2i1svk5 g+TOAJqZ2t7pO8aUtr0rHRhWVoGveDNoSdIGYID9wu6BKyk5lLbOASrbFVP30SUZZV PeEpGHT8XJK2L0gF9Z1dpGQUOd8kP7Fk60r4S2SKXxWX7gazelr6uTfpApeDr1H+L+ kxMUV3BRFbZXA/mSF0JS3d2u+jK+oW+skoqw84U8mWjO/kBEeGSCn+hkTxuh3fdpch pIZ8BGdtmKHOw== Message-ID: Date: Sat, 10 Oct 2026 13:41:04 +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: [PATCH v4 0/2] platform/x86: dell-uart-backlight: fall back to PCH PWM on UART timeout To: chitranshmandhaniya@gmail.com, ilpo.jarvinen@linux.intel.com Cc: platform-driver-x86@vger.kernel.org, linux-kernel@vger.kernel.org, Chitransh_Mandhaniya@dell.com References: <20261009072401.52509-1-chitranshmandhaniya@gmail.com> <20261010102012.110394-1-chitranshmandhaniya@gmail.com> From: Hans de Goede Content-Language: en-US, nl In-Reply-To: <20261010102012.110394-1-chitranshmandhaniya@gmail.com> Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 7bit Hi Chitransh, On 10-Oct-26 12:20 PM, chitranshmandhaniya@gmail.com wrote: > From: Chitransh Mandhaniya > > Some Dell OptiPlex AIO 7410 (35W) ship with DELL0501 in ACPI but no > physical UART scalar board, leaving the machine with zero backlight > control after the UART probe times out. > > Patch 1 is a preparatory refactor that extracts the UART initialization > sequence into dell_uart_bl_init() so the probe function can inspect its > return value. > > Patch 2 adds a PCH PWM fallback path: when dell_uart_bl_init() returns > -ETIMEDOUT, the driver reads the Intel PCH BLC_PWM registers and > registers a BACKLIGHT_PLATFORM device. Thank you for working on this, but directly doing mmio pokes on an mmio range managed by the i915 driver is not okay: NACK for this patch-series / this approach. You should be able to work around this problem by passing: acpi_backlight=native on the kernel command-line which causes acpi_video_get_backlight_type() to properly return native as type. After confirming that that works, you can fix this permanently by extending the existing DMI quirks for this in drivers/acpi/video_detect.c: /* * Dell AIO (All in Ones) which advertise an UART attached backlight * controller board in their ACPI tables (and may even have one), but * which need native backlight control nevertheless. */ { /* https://github.com/zabbly/linux/issues/26 */ .callback = video_detect_force_native, /* Dell OptiPlex 5480 AIO */ .matches = { DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."), DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 5480 AIO"), }, }, { /* https://bugzilla.redhat.com/show_bug.cgi?id=2303936 */ .callback = video_detect_force_native, /* Dell OptiPlex 7760 AIO */ .matches = { DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."), DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 7760 AIO"), }, }, { .callback = video_detect_force_native, /* Dell OptiPlex 7770 AIO */ .matches = { DMI_MATCH(DMI_SYS_VENDOR, "Dell Inc."), DMI_MATCH(DMI_PRODUCT_NAME, "OptiPlex 7770 AIO"), }, }, Regards, Hans > > v3 -> v4: > - Revert __free(pci_dev_put) to manual pci_dev_put() calls to fix > build error when CONFIG_PCI is disabled (kernel test robot) > > v2 -> v3: > - Split into two patches: preparatory refactor + fallback (Ilpo) > > v1 -> v2: > - Use SZ_16 instead of 0x10, add linux/sizes.h (Ilpo) > - Name BIT(31) as PCH_BLC_PWM_ENABLE (Ilpo) > - Fix double-space in block comment (Ilpo) > - Reduce devm_backlight_device_register() to fewer lines (Ilpo) > - Extract dell_uart_bl_init() for the normal UART backlight path (Ilpo) > > Chitransh Mandhaniya (2): > platform/x86: dell-uart-backlight: extract dell_uart_bl_init() from > probe > platform/x86: dell-uart-backlight: fall back to PCH PWM on UART > timeout > > .../platform/x86/dell/dell-uart-backlight.c | 158 +++++++++++++++--- > 1 file changed, 135 insertions(+), 23 deletions(-) >