From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (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 576CE23BF9C; Wed, 10 Dec 2025 14:51:52 +0000 (UTC) Authentication-Results: smtp.subspace.kernel.org; arc=none smtp.client-ip=10.30.226.201 ARC-Seal:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765378312; cv=none; b=Yr2vjG1D/CYgbdX9lFa/OjK+l/W+Os/lR/O84QQx14PSLW2cvGwC/NbYk+SM2FjOUqJU+wfXFVGZlLfAZSrp+WcPz62iPky9BcIO/JD1CR1lYtAHxAvpD5Ft+stdLD1jt+BX/YcO8Dm9KJF9X///UPKIcL/ZEfdrf/5H8ywZ0ds= ARC-Message-Signature:i=1; a=rsa-sha256; d=subspace.kernel.org; s=arc-20240116; t=1765378312; c=relaxed/simple; bh=izr7/LN9/bWfO6kF07G9Tmq+DLJEtc6ivbfspIC/PNs=; h=From:To:Cc:Subject:Date:Message-ID:MIME-Version:Content-Type; b=hZliRnYPbHWF+WjeCn2lyBg/6/hf4ZWfx2dfm/15DvQKRDN+MqecDBEpnm73MN/aI4KPiJ8SSuq3h5Hex5R/gPWjdITWsOWynPcVzA1kfaIX0odjsp7kpe0J1GWGwerm9I1Rsi3sz0ZDg47XdUQbd1UOIz1XcQeYJXTm5Ag8XM0= ARC-Authentication-Results:i=1; smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b=h9VihVKA; arc=none smtp.client-ip=10.30.226.201 Authentication-Results: smtp.subspace.kernel.org; dkim=pass (2048-bit key) header.d=kernel.org header.i=@kernel.org header.b="h9VihVKA" Received: by smtp.kernel.org (Postfix) with ESMTPSA id E5BD0C116B1; Wed, 10 Dec 2025 14:51:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1765378311; bh=izr7/LN9/bWfO6kF07G9Tmq+DLJEtc6ivbfspIC/PNs=; h=From:To:Cc:Subject:Date:From; b=h9VihVKAhv+LhJjQIvD5HPa1QIupAWT4mSBhNycK1KXzYmqhi4op66Aq+9Pp3XJWL XiQw2jTFo2ze6HpUABvzCy9OP2xYIKq9Cfq22sSq0VBZV+KhM1WjuYYqfQLU/a8B0G JLxRyEQCyTRnRZr4DSdSEy/JJC44FEmtt49WcQUMWBjz30U3pF1RmEMcNO/vpUHQrV 0MnHM4ozy1J09iH1yjNht5iQRfF+S6lOO+COVriaBf13TKqsmrCnqUGSIPhFCE56Ek KKxIt12aJCyqDUWa0aQBCpbaFHN3jmDRHq4/TUe73YTj2RUSHhP1xSNyVvmCEJehck wxxGBdrnStWBQ== From: "Rafael J. Wysocki" To: Linux ACPI Cc: LKML , Linux PM , Armin Wolf , Hans de Goede Subject: [PATCH v1 0/3] ACPI: video: Convert ACPI video driver to a platform one Date: Wed, 10 Dec 2025 15:47:34 +0100 Message-ID: <8617910.T7Z3S40VBb@rafael.j.wysocki> Organization: Linux Kernel Development Precedence: bulk X-Mailing-List: linux-pm@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Transfer-Encoding: 7Bit Content-Type: text/plain; charset="UTF-8" Hi All, This is a continuation of https://lore.kernel.org/linux-acpi/2339822.iZASKD2KPV@rafael.j.wysocki/ specifically concerning the ACPI video (backlight) driver which is kind of a special case because ACPI backlight device objects it binds to are ACPI companions of PCI devices (GPUs). The general rationale is the same as for the series linked above. While binding drivers directly to struct acpi_device objects allows basic functionality to be provided, at least in the majority of cases, there are some problems with it, related to general consistency, sysfs layout, power management operation ordering, and code cleanliness. First of all, struct acpi_device objects represent firmware entities rather than hardware and in many cases they provide auxiliary information on devices enumerated independently (like PCI devices or CPUs). It is therefore generally questionable to assign resources to them or create class devices and similar under them because they don't provide functionality associated with those entities by themselves (for example, they don't generate wakeup or input events). As a general rule, a struct acpi_device can only be a parent of another struct acpi_device. If that's not the case, the location of the child device in the device hierarchy is at least confusing and it may not be straightforward to identify the piece of hardware corresponding to that device. Using system suspend and resume callbacks directly with struct acpi_device objects is questionable either because it may cause ordering problems to happen. Namely, struct acpi_device objects are registered before any devices corresponded to by them and they land on the PM list before all of those devices. Consequently, the execution ordering of their PM callbacks may be different from what is generally expected. Moreover, dependencies returned by _DEP objects don't generally affect struct acpi_device objects themselves, only the "physical" device objects associated with them, which potentially is one more source of inconsistency. All of the above means that binding drivers to struct acpi_device "devices" should generally be avoided and so this series converts the ACPI video driver to a platform one. Patches [1-2/3] are preparatory and patch [3/3] is the driver conversion one. Thanks!