linux-kernel - Re: [PATCH v6] ACPI: device_sysfs: Add sysfs support for

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Date:   Mon, 14 Feb 2022 20:11:53 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
To:     Won Chung <wonchung@...gle.com>
Cc:     "Rafael J . Wysocki" <rafael@...nel.org>,
        Len Brown <lenb@...nel.org>,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Benson Leung <bleung@...omium.org>,
        Prashant Malani <pmalani@...omium.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6] ACPI: device_sysfs: Add sysfs support for _PLD

On Fri, Feb 11, 2022 at 3:30 AM Won Chung <wonchung@...gle.com> wrote:
>
> When ACPI table includes _PLD fields for a device, create a new
> directory (pld) in sysfs to share _PLD fields.

This version of the patch loos better to me, but I'm not sure if it
goes into the right direction overall.

> Currently without PLD information, when there are multiple of same
> devices, it is hard to distinguish which device corresponds to which
> physical device in which location. For example, when there are two Type
> C connectors, it is hard to find out which connector corresponds to the
> Type C port on the left panel versus the Type C port on the right panel.

So I think that this is your primary use case and I'm wondering if
this is the best way to address it.

Namely, by exposing _PLD information under the ACPI device object,
you'll make user space wanting to use that information depend on this
interface, but the problem is not ACPI-specific (inevitably, it will
appear on systems using DT, sooner or later) and making the user space
interface related to it depend on ACPI doesn't look like a perfect
choice.

IOW, why don't you create a proper ABI for this in the Type C
subsystem and expose the information needed by user space in a generic
way that can be based on the _PLD information on systems with ACPI?