RE: [PATCH v20 1/4] usb: Add support for Intel LJCA device

[Wu, Wentong]

> From: Shevchenko, Andriy
> On Mon, Oct 16, 2023 at 08:52:28AM +0300, Wu, Wentong wrote:
> > > On 10/13/23 22:05, Shevchenko, Andriy wrote:
> > > > On Thu, Oct 12, 2023 at 01:14:23PM +0200, Hans de Goede wrote:
> 
> <snip>
> 
> > > >> Ah ok, I see. So the code:
> > > >>
> > > >> 1. First tries to find the matching child acpi_device for the
> > > >> auxdev by ADR
> > > >>
> > > >> 2. If 1. fails then falls back to HID + UID matching
> > > >>
> > > >> And there are DSDTs which use either:
> > > >>
> > > >> 1. Only use _ADR to identify which child device is which, like the example
> > > >>    DSDT snippet from the commit msg.
> > > >>
> > > >> 2. Only use _HID + _UID like the 2 example DSDT snippets from me
> > > >> email
> > > >>
> > > >> But there never is a case where both _ADR and _HID are used at
> > > >> the same time (which would be an ACPI spec violation as Andy said).
> > > >>
> > > >> So AFAICT there is no issue here since  _ADR and _HID are never
> > > >> user at the same time and the commit message correctly describes
> > > >> scenario 1. from above, so the commit message is fine too.
> > > >>
> > > >> So I believe that we can continue with this patch series in its
> > > >> current v20 form, which has already been staged for going into
> > > >> -next by Greg.
> > > >>
> > > >> Andy can you confirm that moving ahead with the current version
> > > >> is ok ?
> > > >
> > > > Yes as we have a few weeks to fix corner cases.
> > > >
> > > > What I'm worrying is that opening door for _ADR that seems never
> > > > used is kinda an overkill here (resolving non-existing problem).
> > >
> > > I assume that there actually some DSDTs using the _ADR approach and
> > > that this support is not there just for fun.
> >
> > right, it's not for fun, we use _ADR here is to reduce the maintain
> > effort because currently it defines _HID for every new platform and
> > the drivers have to be updated accordingly, while _ADR doesn't have that
> problem.
> 
> But this does not confirm if you have such devices. Moreover, My question
> about _CID per function stays the same. Why firmware is not using it?

Yes, both _ADR and _CID can stop growing list in the driver. And for _ADR, it also
only require one ID per function. I don't know why BIOS team doesn't select _CID,
but I have suggested use _ADR internally, and , to make things moving forward,
the driver adds support for _ADR here first. 

But you're right, _CID is another solution as well, we will discuss it with firmware
team more.

> In that case you need only one ID per function in the driver (it might require some
> IDs in the _HID, I don't remember that part of the spec by heart, i.e.  if _CID can be
> only provided with existing _HID or not).
> 
> > > Wentong, can you confirm that the _ADR using codepaths are actually
> > > used on some hardware / with some DSDTs out there ?
> >
> > what I can share is that we will see.
> >
> > > > Looking at the design of the
> > > > driver I'm not sure why ACPI HIDs are collected somewhere else
> > > > than in the respective drivers.
> >
> > AFAIK, auxiliary bus doesn't support parsing fwnodes currently.
> > Probably we can support it for auxiliary bus in another patch.
> 
> This is good idea!
> 
> 
> > > > And looking at the ID lists themselves I am not sure why the
> > > > firmware of the respective hardware platforms are not using
> > > _CID.
> >
> > I think firmware can select _CID as well, but the shipped hw doesn't
> > use _CID, the driver has to make sure the shipped hw working as well.
> > And switching to _CID for the shipped hw is not easy, and it has to change
> windows driver as well.
> 
> I understand, but at least you may stop growing list in the driver.
Yes, 

> And actually using separate IDs for multifunctional device seems not ideal
> solution to me.
Agree, I will consider _CID more, but currently to avoid this and also support
shipped hardware, _ADR is at least a choice.

BR,
Wentong

> > > This is a USB device which has 4 functions:
> 
> Yes, I understand this part, but thank you for elaboration about auxbus, which
> seems lack of needed support. And I would really like to see someone adds it
> there.
> 
> > > 1. GPIO controller
> > > 2. I2C controller 1
> > > 3. I2C controller 2
> > > 4. SPI controller
> > >
> > > The driver for the main USB interface uses the new auxbus to create
> > > 4 child devices. The _ADR or if that fails _HID + _UID matching is
> > > done to find the correct acpi_device child of the acpi_device which
> > > is the ACPI-companion of the main USB device.
> > >
> > > After looking up the correct acpi_device child this is then set as
> > > the fwnode / ACPI-companion of the auxbus device created for that function.
> > >
> > > Having the correct fwnode is important because other parts of the
> > > DSDT reference this fwnode to specify GPIO / I2C / SPI resources and
> > > if the fwnode of the aux-device is not set correctly then the
> > > resources for other devices referencing it (typically a camera
> > > sensor) can not be found.
> > >
> > > As for why the driver for the auxbus devices / children do not use
> > > HID matching, AFAIK the auxbus has no support for using ACPI (or DT)
> > > matching for aux-devices and these drivers need to be
> > > auxiliary_driver's and bind to the auxbus device and not to a
> > > platform_device instantiated for the acpi_device since they need the auxbus
> device to access the USB device.
> >
> > Yes, total agree. Thanks
> 
> --
> With Best Regards,
> Andy Shevchenko
>