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

[Laurent Pinchart]

Hi Andy,

On Fri, Oct 30, 2020 at 12:22:15AM +0200, Andy Shevchenko wrote:
> On Thu, Oct 29, 2020 at 11:29:30PM +0200, Laurent Pinchart wrote:
> > 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.
> 
> In this case we probably need something like
> 
> struct acpi_device *
> acpi_dev_get_next_match_dev(struct acpi_device *adev,
> 			    const char *hid, const char *uid, s64 hrv)
> {
> 	struct device *start = adev ? &adev->dev : NULL;
> 	...
> 	dev = bus_find_device(&acpi_bus_type, start, &match, acpi_dev_match_cb);
> 	...
> }
> 
> in drivers/acpi/utils.c and
> 
> static inline struct acpi_device *
> acpi_dev_get_first_match_dev(const char *hid, const char *uid, s64 hrv)
> {
> 	return acpi_dev_get_next_match_dev(NULL, hid, uid, hrv);
> }
> 
> in include/linux/acpi.h.
> 
> Then we may add
> 
> #define for_each_acpi_dev_match(adev, hid, uid, hrv)			\
> 	for (adev = acpi_dev_get_first_match_dev(hid, uid, hrv);	\
> 	     adev;							\
> 	     adev = acpi_dev_get_next_match_dev(adev, hid, uid, hrv))

What the cio2-bridge code needs is indeed

	for each hid in supported hids:
		for each acpi device that is compatible with hid:
			...

which could also be expressed as

	for each acpi device:
		if acpi device hid is in supported hids:
			...

I don't mind either option, I'll happily follow the preference of the
ACPI maintainers.

-- 
Regards,

Laurent Pinchart