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

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

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]

I just sent an update to Documentation with the link to[1]. 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.

--
Regards,
Sudeep

[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