On Tue, Feb 15, 2022 at 03:04:54PM +0100, Rafael J. Wysocki wrote: > Adding Greg, who should be involved in this discussion IMO. > > On Mon, Feb 14, 2022 at 11:59 PM Won Chung <wonchung@xxxxxxxxxx> wrote: > > > > On Mon, Feb 14, 2022 at 12:30 PM Won Chung <wonchung@xxxxxxxxxx> wrote: > > > > > > On Mon, Feb 14, 2022 at 11:12 AM Rafael J. Wysocki <rafael@xxxxxxxxxx> wrote: > > > > > > > > On Fri, Feb 11, 2022 at 3:30 AM Won Chung <wonchung@xxxxxxxxxx> 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? > > _PLD is an interface defined by ACPI, but its purpose is not ACPI-specific. > > > 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. > > Right. > > > > > > > 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! > > I don't really think that this is a Type C problem either. > > It has existed for a long time in the USB world, for example, or > wherever there are user-accessible ports, but it looks like in the > Type C case it has become vitally important. > > My point is that writing user space depending on accessing _PLD > information exposed under an ACPI device interface that only > corresponds to the device in question and in the ACPI-specific format > would be a mistake (Greg, please let me know if you disagree). That's > because (a) it would depend on ACPI tables being present (so it > wouldn't work on systems without them) and (b) it would depend on the > format of data which covers information that isn't likely to be > relevant. > > If this information is exposed by the kernel verbatim and user space > depending on this information is created, it will not be possible to > unexpose it even if it turns out that exposing it has been a mistake. > > OTOH, if only the relevant pieces of information are exposed in a > generic way, it is always possible to expose more pieces of it in the > future as needed. There are pending patches on the linux-usb mailing list from Heikki to help expand on the typec information in sysfs in a generic way. Won, please work with the linux-usb developers on this change and do not do anything that is ACPI-specific and only. That way will not be good for anyone involved. Please see: https://lore.kernel.org/r/20220203144657.16527-1-heikki.krogerus@xxxxxxxxxxxxxxx for the current discussion. thanks, greg k-h
