On Wed, Nov 22, 2023 at 5:58 AM Raag Jadav <raag.jadav@xxxxxxxxx> wrote:
>
> On Tue, Nov 21, 2023 at 08:25:20PM +0100, Rafael J. Wysocki wrote:
> > On Tue, Nov 21, 2023 at 11:38 AM Raag Jadav <raag.jadav@xxxxxxxxx> wrote:
> > >
> > > According to ACPI specification, a _UID object can evaluate to either
> > > a numeric value or a string. Update acpi_dev_uid_match() helper to
> > > support _UID matching for both integer and string types.
> > >
> > > Suggested-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> > > Suggested-by: Mika Westerberg <mika.westerberg@xxxxxxxxxxxxxxx>
> > > Suggested-by: Rafael J. Wysocki <rafael.j.wysocki@xxxxxxxxx>
> >
> > You need to be careful with using this. There are some things below
> > that go beyond what I have suggested.
>
> I think we all suggested some bits and pieces so I included everyone.
> We can drop if there are any objections.
There are, from me and from Andy.
[cut]
> > Up to this point it is all fine IMV.
> >
> > > +/**
> > > + * acpi_dev_uid_match - Match device by supplied UID
> > > + * @adev: ACPI device to match.
> > > + * @uid2: Unique ID of the device.
> > > + *
> > > + * Matches UID in @adev with given @uid2.
> > > + *
> > > + * Returns: %true if matches, %false otherwise.
> > > + */
> > > +
> > > +/* Treat uid as a string for array and pointer types, treat as an integer otherwise */
> > > +#define get_uid_type(x) \
> > > + (__builtin_choose_expr(is_array_or_pointer_type(x), (const char *)0, (u64)0))
> >
> > But I wouldn't use the above.
> >
> > It is far more elaborate than needed for this use case and may not
> > actually work as expected. For instance, why would a pointer to a
> > random struct type be a good candidate for a string?
>
> Such case will not compile, since its data type will not match with
> acpi_str_uid_match() prototype. The compiler does a very good job of
> qualifing only the compatible string types here, which is exactly what
> we want.
>
> error: passing argument 2 of 'acpi_str_uid_match' from incompatible pointer type [-Werror=incompatible-pointer-types]
> if (acpi_dev_uid_match(adev, adev)) {
> ^
> ./include/acpi/acpi_bus.h:870:20: note: expected 'const char *' but argument is of type 'struct acpi_device *'
> static inline bool acpi_str_uid_match(struct acpi_device *adev, const char *uid2)
You are right, it won't compile, but that's not my point. Why would
it be matched with acpi_str_uid_match() in the first place?
> > > +
> > > +#define acpi_dev_uid_match(adev, uid2) \
> > > + _Generic(get_uid_type(uid2), \
> > > + const char *: acpi_str_uid_match, \
> > > + u64: acpi_int_uid_match)(adev, uid2)
> > > +
> >
> > Personally, I would just do something like the following
> >
> > #define acpi_dev_uid_match(adev, uid2) \
> > _Generic((uid2), \
> > const char *: acpi_str_uid_match, \
> > char *: acpi_str_uid_match, \
> > const void *: acpi_str_uid_match, \
> > void *: acpi_str_uid_match, \
> > default: acpi_int_uid_match)(adev, uid2)
> >
> > which doesn't require compiler.h to be fiddled with and is rather
> > straightforward to follow.
> >
> > If I'm to apply the patches, this is about the level of complexity you
> > need to target.
>
> Understood, however this will limit the type support to only a handful
> of types,
Indeed.
> and will not satisfy a few of the existing users, which, for
> example are passing signed or unsigned pointer or an array of u8.
Fair enough, so those types would need to be added to the list.
> Listing every possible type manually for _Generic() looks a bit verbose
> for something that can be simply achieved by __builtin functions in my
> opinion.
But then you don't even need _Generic(), do you?
Wouldn't something like the below work?
#define acpi_dev_uid_match(adev, uid2) \
(__builtin_choose_expr(is_array_or_pointer_type((uid2)),acpi_str_uid_match(adev,
uid2), acpi_int_uid_match(adev, uid2))
In any case, I'm not particularly convinced about the
is_array_or_pointer_type() thing and so I'm not going to apply the
series as is.
