Re: [PATCH 1/3] drm/xe: Introduce IF_ARGS macro utility

[Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>]

On 12/12/2025 9:34 AM, Michal Wajdeczko wrote:
> We want to extend our macro-based KLV list definitions with new
> information about the version from which given KLV is supported.
> Add utility IF_ARGS macro that can be used in code generators to
> emit different code based on the presence of additional arguments.
>
> Introduce macro itself and extend our kunit tests to cover it.
> We will use this macro in next patch.
>
> Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
> ---
>   drivers/gpu/drm/xe/tests/xe_args_test.c | 53 +++++++++++++++++++++++++
>   drivers/gpu/drm/xe/xe_args.h            | 18 +++++++++
>   2 files changed, 71 insertions(+)
>
> diff --git a/drivers/gpu/drm/xe/tests/xe_args_test.c b/drivers/gpu/drm/xe/tests/xe_args_test.c
> index f3fb23aa5d2e..d11ea610f67a 100644
> --- a/drivers/gpu/drm/xe/tests/xe_args_test.c
> +++ b/drivers/gpu/drm/xe/tests/xe_args_test.c
> @@ -78,6 +78,24 @@ static void pick_arg_example(struct kunit *test)
>   #undef buz
>   }
>   
> +static void if_args_example(struct kunit *test)
> +{
> +	enum { Z = 1, Q };
> +
> +#define foo	X, Y
> +#define bar	IF_ARGS(Z, Q, foo)
> +#define buz	IF_ARGS(Z, Q, DROP_FIRST_ARG(FIRST_ARG(foo)))
> +
> +	KUNIT_EXPECT_EQ(test, bar, Z);
> +	KUNIT_EXPECT_EQ(test, buz, Q);
> +	KUNIT_EXPECT_STREQ(test, __stringify(bar), "Z");
> +	KUNIT_EXPECT_STREQ(test, __stringify(buz), "Q");
> +
> +#undef foo
> +#undef bar
> +#undef buz
> +}
> +
>   static void sep_comma_example(struct kunit *test)
>   {
>   #define foo(f)	f(X) f(Y) f(Z) f(Q)
> @@ -198,6 +216,39 @@ static void last_arg_test(struct kunit *test)
>   	KUNIT_EXPECT_STREQ(test, __stringify(LAST_ARG(MAX_ARGS)), "-12");
>   }
>   
> +static void if_args_test(struct kunit *test)
> +{
> +	bool with_args = true;
> +	bool no_args = false;
> +	enum { X = 100 };
> +
> +	KUNIT_EXPECT_TRUE(test, IF_ARGS(true, false, FOO_ARGS));
> +	KUNIT_EXPECT_FALSE(test, IF_ARGS(true, false, NO_ARGS));
> +
> +	KUNIT_EXPECT_TRUE(test, CONCATENATE(IF_ARGS(with, no, FOO_ARGS), _args));
> +	KUNIT_EXPECT_FALSE(test, CONCATENATE(IF_ARGS(with, no, NO_ARGS), _args));
> +
> +	KUNIT_EXPECT_STREQ(test, __stringify(IF_ARGS(yes, no, FOO_ARGS)), "yes");
> +	KUNIT_EXPECT_STREQ(test, __stringify(IF_ARGS(no, no, NO_ARGS)), "no");
> +
> +	KUNIT_EXPECT_EQ(test, IF_ARGS(CALL_ARGS(COUNT_ARGS, FOO_ARGS), -1, FOO_ARGS), 4);
> +	KUNIT_EXPECT_EQ(test, IF_ARGS(CALL_ARGS(COUNT_ARGS, FOO_ARGS), -1, NO_ARGS), -1);
> +	KUNIT_EXPECT_EQ(test, IF_ARGS(CALL_ARGS(COUNT_ARGS, NO_ARGS), -1, FOO_ARGS), 0);
> +	KUNIT_EXPECT_EQ(test, IF_ARGS(CALL_ARGS(COUNT_ARGS, NO_ARGS), -1, NO_ARGS), -1);
> +
> +	KUNIT_EXPECT_EQ(test,
> +			FIRST_ARG(CONCATENATE(CALL_ARGS(IF_ARGS, FOO, MAX, FOO_ARGS), _ARGS)), X);
> +	KUNIT_EXPECT_EQ(test,
> +			FIRST_ARG(CONCATENATE(CALL_ARGS(IF_ARGS, FOO, MAX, NO_ARGS), _ARGS)), -1);
> +
> +	KUNIT_EXPECT_EQ(test,
> +			CALL_ARGS(COUNT_ARGS,
> +				  CONCATENATE(CALL_ARGS(IF_ARGS, FOO, MAX, FOO_ARGS), _ARGS)), 4);
> +	KUNIT_EXPECT_EQ(test,
> +			CALL_ARGS(COUNT_ARGS,
> +				  CONCATENATE(CALL_ARGS(IF_ARGS, FOO, MAX, NO_ARGS), _ARGS)), 12);
> +}
> +
>   static struct kunit_case args_tests[] = {
>   	KUNIT_CASE(count_args_test),
>   	KUNIT_CASE(call_args_example),
> @@ -209,6 +260,8 @@ static struct kunit_case args_tests[] = {
>   	KUNIT_CASE(last_arg_example),
>   	KUNIT_CASE(last_arg_test),
>   	KUNIT_CASE(pick_arg_example),
> +	KUNIT_CASE(if_args_example),
> +	KUNIT_CASE(if_args_test),
>   	KUNIT_CASE(sep_comma_example),
>   	{}
>   };
> diff --git a/drivers/gpu/drm/xe/xe_args.h b/drivers/gpu/drm/xe/xe_args.h
> index 4dbc7e53c624..b24e6d3349bb 100644
> --- a/drivers/gpu/drm/xe/xe_args.h
> +++ b/drivers/gpu/drm/xe/xe_args.h
> @@ -121,6 +121,24 @@
>   #define PICK_ARG11(args...)		PICK_ARG10(DROP_FIRST_ARG(args))
>   #define PICK_ARG12(args...)		PICK_ARG11(DROP_FIRST_ARG(args))
>   
> +/**
> + * IF_ARGS() - Make selection based on optional argument list.
> + * @then: token to return if arguments are present
> + * @else: token to return if arguments are empty
> + * @...: arguments to check (optional)
> + *
> + * This macro allows to select a token based on the presence of the argumen list.
> + *
> + * Example:
> + *
> + *	#define foo	X, Y
> + *	#define bar	IF_ARGS(Z, Q, foo)
> + *	#define buz	IF_ARGS(Z, Q, DROP_FIRST_ARG(FIRST_ARG(foo)))
> + *
> + *	With above definitions bar expands to Z while buz expands to Q.
> + */
> +#define IF_ARGS(then, else, ...)	FIRST_ARG(__VA_OPT__(then,) else)

A bit confused about the __VA_OPT__ support since it is officially a C23 
extension and the kernel build uses gnu11, but it looks like it is 
supported as part of GNU C since GCC 8 (the minimum GCC version for 
kernel builds is currently 8.1), so we're probably ok.
It is already used in a couple of places in the kernel (with only one of 
them having a GCC version check AFAICS), so I won't block on this, but 
please get a second pair of eyes to confirm this is ok.

Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>

Daniele

> +
>   /**
>    * ARGS_SEP_COMMA - Definition of a comma character.
>    *