x86/cpuid: Move CPUID(0x2) APIs into <cpuid/api.h>

Move all of the CPUID(0x2) APIs at <cpuid/leaf_0x2_api.h> into
<cpuid/api.h>, in order centralize all CPUID APIs into the latter.

While at it, separate the different CPUID leaf parsing APIs using
header comments like "CPUID(0xN) parsing: ".

Suggested-by: Ingo Molnar <mingo@kernel.org>
Signed-off-by: Ahmed S. Darwish <darwi@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Andrew Cooper <andrew.cooper3@citrix.com>
Cc: John Ogness <john.ogness@linutronix.de>
Cc: x86-cpuid@lists.linux.dev
Link: https://lore.kernel.org/r/20250508150240.172915-2-darwi@linutronix.de

Author: Ahmed S. Darwish

arch/x86/include/asm/cpuid.h

@@ -4,6 +4,5 @@
 #define _ASM_X86_CPUID_H
 
 #include <asm/cpuid/api.h>
-#include <asm/cpuid/leaf_0x2_api.h>
 
 #endif /* _ASM_X86_CPUID_H */

arch/x86/include/asm/cpuid/api.h

@@ -160,6 +160,10 @@ static inline void __cpuid_read_reg(u32 leaf, u32 subleaf,
 	__cpuid_read_reg(leaf, 0, regidx, (u32 *)(reg));	\
 }
 
+/*
+ * Hypervisor-related APIs:
+ */
+
 static __always_inline bool cpuid_function_is_indexed(u32 function)
 {
 	switch (function) {
@@ -208,7 +212,76 @@ static inline u32 hypervisor_cpuid_base(const char *sig, u32 leaves)
 }
 
 /*
- * CPUID(0x80000006) parsing helpers
+ * CPUID(0x2) parsing:
+ */
+
+/**
+ * cpuid_get_leaf_0x2_regs() - Return sanitized leaf 0x2 register output
+ * @regs:	Output parameter
+ *
+ * Query CPUID leaf 0x2 and store its output in @regs.	Force set any
+ * invalid 1-byte descriptor returned by the hardware to zero (the NULL
+ * cache/TLB descriptor) before returning it to the caller.
+ *
+ * Use for_each_leaf_0x2_entry() to iterate over the register output in
+ * parsed form.
+ */
+static inline void cpuid_get_leaf_0x2_regs(union leaf_0x2_regs *regs)
+{
+	cpuid_leaf(0x2, regs);
+
+	/*
+	 * All Intel CPUs must report an iteration count of 1.	In case
+	 * of bogus hardware, treat all returned descriptors as NULL.
+	 */
+	if (regs->desc[0] != 0x01) {
+		for (int i = 0; i < 4; i++)
+			regs->regv[i] = 0;
+		return;
+	}
+
+	/*
+	 * The most significant bit (MSB) of each register must be clear.
+	 * If a register is invalid, replace its descriptors with NULL.
+	 */
+	for (int i = 0; i < 4; i++) {
+		if (regs->reg[i].invalid)
+			regs->regv[i] = 0;
+	}
+}
+
+/**
+ * for_each_leaf_0x2_entry() - Iterator for parsed leaf 0x2 descriptors
+ * @regs:   Leaf 0x2 register output, returned by cpuid_get_leaf_0x2_regs()
+ * @__ptr:  u8 pointer, for macro internal use only
+ * @entry:  Pointer to parsed descriptor information at each iteration
+ *
+ * Loop over the 1-byte descriptors in the passed leaf 0x2 output registers
+ * @regs.  Provide the parsed information for each descriptor through @entry.
+ *
+ * To handle cache-specific descriptors, switch on @entry->c_type.  For TLB
+ * descriptors, switch on @entry->t_type.
+ *
+ * Example usage for cache descriptors::
+ *
+ *	const struct leaf_0x2_table *entry;
+ *	union leaf_0x2_regs regs;
+ *	u8 *ptr;
+ *
+ *	cpuid_get_leaf_0x2_regs(&regs);
+ *	for_each_leaf_0x2_entry(regs, ptr, entry) {
+ *		switch (entry->c_type) {
+ *			...
+ *		}
+ *	}
+ */
+#define for_each_leaf_0x2_entry(regs, __ptr, entry)				\
+	for (__ptr = &(regs).desc[1];						\
+	     __ptr < &(regs).desc[16] && (entry = &cpuid_0x2_table[*__ptr]);	\
+	     __ptr++)
+
+/*
+ * CPUID(0x80000006) parsing:
  */
 
 static inline bool cpuid_amd_hygon_has_l3_cache(void)

arch/x86/include/asm/cpuid/leaf_0x2_api.h

@@ -31,8 +31,7 @@ enum cpuid_regs_idx {
 #define CPUID_LEAF_TILE		0x1d
 
 /*
- * Types for CPUID(0x2) parsing
- * Check <asm/cpuid/leaf_0x2_api.h>
+ * Types for CPUID(0x2) parsing:
  */
 
 struct leaf_0x2_reg {