Re: [RFC PATCH v3 9/9] ipu3-cio2: Add functionality allowing software_node connections to sensors on platforms designed for Windows

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

On Thu, Oct 29, 2020 at 10:26:56PM +0200, Andy Shevchenko wrote:
> On Thu, Oct 29, 2020 at 10:21 PM Laurent Pinchart wrote:
> > On Mon, Oct 26, 2020 at 06:10:50PM +0200, Andy Shevchenko wrote:
> > > On Sat, Oct 24, 2020 at 12:37:02PM +0300, Laurent Pinchart wrote:
> > > > On Sat, Oct 24, 2020 at 09:50:07AM +0100, Dan Scally wrote:
> > > > > On 24/10/2020 02:24, Laurent Pinchart wrote:
> > > > > > On Mon, Oct 19, 2020 at 11:59:03PM +0100, Daniel Scally wrote:
> > >
> > > > > >> +              adev = acpi_dev_get_first_match_dev(supported_devices[i], NULL, -1);
> > > > > >
> > > > > > What if there are multiple sensor of the same model ?
> > > > >
> > > > > Hmm, yeah, that would be a bit of a pickle. I guess the newer
> > > > > smartphones have multiple sensors on the back, which I presume are the
> > > > > same model. So that will probably crop up at some point. How about
> > > > > instead I use bus_for_each_dev() and in the applied function check if
> > > > > the _HID is in the supported list?
> > > >
> > > > Sounds good to me.
> > > >
> > > > > >> +              if (!adev)
> > > > > >> +                      continue;
> > >
> > > Please, don't.
> > >
> > > If we have so weird ACPI tables it must be w/a differently. The all, even badly
> > > formed, ACPI tables I have seen so far are using _UID to distinguish instance
> > > of the device (see second parameter to the above function).
> > >
> > > If we meet the very broken table I would like rather to know about, then
> > > silently think ahead what could be best.
> > >
> > > I.o.w. don't change this until we will have a real example of the problematic
> > > firmware.
> >
> > I'm not sure to follow you. Daniel's current code loops over all the
> > supported HID (as stored in the supported_devices table), and then gets
> > the first ACPI device for each of them. If multiple ACPI devices exist
> > with the same HID, we need to handle them all, so enumerating all ACPI
> > devices and checking whether their HID is one we handle seems to be the
> > right option to me.
> 
> Devices with the same HID should be still different by another
> parameter in ACPI. The above mentioned call just uses the rough
> estimation for relaxed conditions. If you expect more than one device
> with the same HID how do you expect to distinguish them? The correct
> way is to use _UID. It may be absent, or set to a value. And this
> value should be unique (as per U letter in UID abbreviation). That
> said, the above is good enough till we find the firmware with the
> above true (several devices with the same HID). Until then the code is
> fine.

I expect those devices with the same _HID to have different _UID values,
yes. On the systems I've seen so far, that assumption is not violated,
and I don't think we need to already plan how we will support systems
where multiple devices would have the same _HID and _UID (within the
same scope). There's no disagreement there.

My point is that supported_devices stores HID values, and doesn't care
about UID. The code loops over supported_devices, and for each entry,
calls acpi_dev_get_first_match_dev() and process the ACPI devices
returned by that call. We thus process at most one ACPI device per HID,
which isn't right.

-- 
Regards,

Laurent Pinchart