Re: [net-next: PATCH 09/12] Documentation: ACPI: DSD: introduce DSA description

[Sudeep Holla <sudeep.holla@arm.com>]

On Tue, Jun 21, 2022 at 06:00:42PM +0200, Rafael J. Wysocki wrote:
> On Tue, Jun 21, 2022 at 5:37 PM Sudeep Holla <sudeep.holla@arm.com> wrote:
> >
> > On Tue, Jun 21, 2022 at 05:23:30PM +0200, Rafael J. Wysocki wrote:
> > > On Tue, Jun 21, 2022 at 3:28 PM Sudeep Holla <sudeep.holla@arm.com> wrote:
> > > >
> > > > On Tue, Jun 21, 2022 at 01:24:51PM +0200, Andrew Lunn wrote:
> > > > > On Tue, Jun 21, 2022 at 02:15:41PM +0300, Andy Shevchenko wrote:
> > > > > > On Tue, Jun 21, 2022 at 10:45:56AM +0100, Sudeep Holla wrote:
> > > > > > > On Mon, Jun 20, 2022 at 05:02:22PM +0200, Marcin Wojtas wrote:
> > > > > > > > Describe the Distributed Switch Architecture (DSA) - compliant
> > > > > > > > MDIO devices. In ACPI world they are represented as children
> > > > > > > > of the MDIO busses, which are responsible for their enumeration
> > > > > > > > based on the standard _ADR fields and description in _DSD objects
> > > > > > > > under device properties UUID [1].
> > > > > > > >
> > > > > > > > [1] http://www.uefi.org/sites/default/files/resources/_DSD-device-properties-UUID.pdf
> > > > > >
> > > > > > > Why is this document part of Linux code base ?
> > > > > >
> > > > > > It's fine, but your are right with your latter questions.
> > > > > >
> > > > > > > How will the other OSes be aware of this ?
> > > > > >
> > > > > > Should be a standard somewhere.
> > > > > >
> > > > > > > I assume there was some repository to maintain such DSDs so that it
> > > > > > > is accessible for other OSes. I am not agreeing or disagreeing on the
> > > > > > > change itself, but I am concerned about this present in the kernel
> > > > > > > code.
> > > > > >
> > > > > > I dunno we have a such, but the closest I may imagine is MIPI standardization,
> > > > > > that we have at least for cameras and sound.
> > > > > >
> > > > > > I would suggest to go and work with MIPI for network / DSA / etc area, so
> > > > > > everybody else will be aware of the standard.
> > > > >
> > > > > It is the same argument as for DT. Other OSes and bootloaders seem to
> > > > > manage digging around in Linux for DT binding documentation. I don't
> > > > > see why bootloaders and other OSes can not also dig around in Linux
> > > > > for ACPI binding documentations.
> > > > >
> > > >
> > > > Theoretically you are right. But in DT case majority of non-standard(by
> > > > standard I am referring to the one's in Open Firmware specification) are
> > > > in the kernel. But that is not true for ACPI. And that is the reason for
> > > > objecting it. One of the main other OS using ACPI may not look here for
> > > > any ACPI bindings(we may not care, but still OS neutral place is better
> > > > for this).
> > > >
> > > > > Ideally, somebody will submit all this for acceptance into ACPI, but
> > > > > into somebody does, i suspect it will just remain a defacto standard
> > > > > in Linux.
> > > > >
> > > >
> > > > DSD is not integral part of ACPI spec, so the process is never clear.
> > > > However there is this project[1], IIUC it is just guidance and doesn't
> > > > include any bindings IIUC. But we need something similar here for better
> > > > visibility and to remain OS agnostic. Even with DT, there is a strong
> > > > desire to separate it out, but it has grown so much that it is getting
> > > > harder to do that with every release. I was just trying to avoid getting
> > > > into that situation.
> > > >
> > > > [1] https://github.com/UEFI/DSD-Guide
> > >
> > > Here's my personal take on this.
> > >
> > > This patch series essentially makes the kernel recognize a few generic
> > > (that is, not tied on any specific device ID) device properties
> > > supplied by the firmware via _DSD.  They are generic, because there is
> > > some library code in the kernel that can consume them and that library
> > > code is used in multiple places (and it is better to supply data from
> > > the firmware directly to it).
> > >
> > > If we all agree that it is a good idea for the kernel to allow these
> > > properties to be supplied via _DSD this way, there is no reason to
> > > avoid admitting that fact in the kernel documentation.
> > >
> > > IMV, there's nothing wrong with stating officially that these
> > > properties are recognized by the kernel and what they are used for and
> > > it has no bearing on whether or not they are also used by someone
> > > else.
> >
> > Good point. I was also suggested to make properties have prefix "linux-"
> > similar to "uefi-" in the set of DSD properties list @[1]. In that case
> > it makes more sense to maintain in the kernel. If they add "uefi-" prefix,
> > I was also told that it can be hosted @[1] as specific in section 3.1.4 @[2]
> 
> Well, the point here is to use the same property names on both the DT
> and ACPI ends IIUC and there's certain value in doing that.
> 
> The library in question already uses these names with DT and there is
> no real need to change that.
>

Make sense and I agree.

> Of course, if the platform firmware supplies these properties in a way
> described in the document in question, it will be a provision
> specifically for Linux and nothing else (unless that hypothetical
> other thing decides to follow Linux in this respect, that is).  As
> long as that is clear, I don't see why it would be better to introduce
> different property names just for _DSD.
>

Understood and very valid point.

> > I just sent an update to Documentation with the link to[1].
> 
> Thanks!
> 
> > I can also
> > update the same to mention about the process as described in section 3.1.4
> > if that helps and we are happy to follow that in the kernel.
> >
> > [1] https://github.com/UEFI/DSD-Guide
> > [2] https://github.com/UEFI/DSD-Guide/blob/main/src/dsd-guide.adoc#314-adding-uefi-device-properties
> 
> IMV it would be useful to add that information, but IMO the process is
> mostly relevant for new use cases, when someone wants to introduce an
> entirely new property that is not yet covered by the DT bindings.
> 
> In the cases when the existing DT properties are the closest thing to
> a standard way of supplying the OS with the information in question it
> is most appealing to use the property names that are in use already.

Agreed, I wasn't aware that the properties discussed in $subject are already
DT properties. I agree on the point that we don't want to have a different
one(with prefix) if the DT properties are already supported.

--
Regards,
Sudeep