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From:   Won Chung <wonchung@google.com>
Date:   Mon, 14 Feb 2022 14:58:44 -0800
Message-ID: <CAOvb9yh7jo27NH32tbAOtkJrnC9LwUFgFbHRbdbArwiU+YSmdw@mail.gmail.com>
Subject: Re: [PATCH v6] ACPI: device_sysfs: Add sysfs support for _PLD
To:     "Rafael J. Wysocki" <rafael@kernel.org>
Cc:     Len Brown <lenb@kernel.org>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        Benson Leung <bleung@chromium.org>,
        Prashant Malani <pmalani@chromium.org>,
        ACPI Devel Maling List <linux-acpi@vger.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@vger.kernel.org>
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On Mon, Feb 14, 2022 at 12:30 PM Won Chung <wonchung@google.com> wrote:
>
> On Mon, Feb 14, 2022 at 11:12 AM Rafael J. Wysocki <rafael@kernel.org> wrote:
> >
> > On Fri, Feb 11, 2022 at 3:30 AM Won Chung <wonchung@google.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?
>
> Hi Rafael,
>
> Thank you for the review.
>
> I was thinking that _PLD info is specific to ACPI since it is part of
> the ACPI table. Could you explain a little bit more on why you think
> exposing _PLD fields is not an ACPI-specific problem?

Hi Rafael again,

Sorry for the silly question here. I misunderstood your comment a bit,
but I talked to Benson and Prashant for clarification. I understand
now what you mean by it is not an ACPI-specific problem and exposing
PLD would depend on ACPI.

>
> I gave an example of how _PLD fields can be used for specifying Type C
> connectors, but it is not Type C specific. For Chrome OS, we plan to
> initially add PLD to not only Type C connectors but also USB port
> devices (including Type C and Type A). Also, PLD can be used in the
> future for describing other types of ports too like HDMI. (Benson and
> Prashant, please correct or add if I am wrong or missing some
> information) Maybe my commit message was not detailed enough..
>
> I am also curious what Heikki thinks about this. Heikki, can you take
> a look and share your thoughts?

I am still curious what you and Heikki think about this since it may
not be a Type C specific issue. We can start from adding generic
location info to Type C subsystem first, as you suggested, then
consider how to do the same for USB devices and Type A ports
afterwards. I would appreciate sharing any thoughts or feedback. Thank
you very much!

Won

>
> Thank you,
> Won