x86/cpu: Refresh DCA leaf reading code

The DCA leaf number is also hard-coded in the CPUID level dependency
table. Move its definition to common code and use it.

While at it, fix up the naming and types in the probe code.  All
CPUID data is provided in 32-bit registers, not 'unsigned long'.
Also stop referring to "level_9".  Move away from test_bit()
because the type is no longer an 'unsigned long'.

Signed-off-by: Dave Hansen <[email protected]>
Reviewed-by: Zhao Liu <[email protected]>
Link: https://lore.kernel.org/all/20241213205032.476A30FE%40davehans-spike.ostc.intel.com

Author: hansendc

arch/x86/include/asm/cpuid.h

@@ -21,7 +21,8 @@ enum cpuid_regs_idx {
 	CPUID_EDX,
 };
 
-#define CPUID_MWAIT_LEAF		5
+#define CPUID_MWAIT_LEAF	0x5
+#define CPUID_DCA_LEAF		0x9
 
 #ifdef CONFIG_X86_32
 bool have_cpuid_p(void);

arch/x86/kernel/cpu/common.c

@@ -638,7 +638,7 @@ struct cpuid_dependent_feature {
 static const struct cpuid_dependent_feature
 cpuid_dependent_features[] = {
 	{ X86_FEATURE_MWAIT,		CPUID_MWAIT_LEAF },
-	{ X86_FEATURE_DCA,		0x00000009 },
+	{ X86_FEATURE_DCA,		CPUID_DCA_LEAF },
 	{ X86_FEATURE_XSAVE,		0x0000000d },
 	{ 0, 0 }
 };

drivers/dma/ioat/dca.c

@@ -10,6 +10,8 @@
 #include <linux/interrupt.h>
 #include <linux/dca.h>
 
+#include <asm/cpuid.h>
+
 /* either a kernel change is needed, or we need something like this in kernel */
 #ifndef CONFIG_SMP
 #include <asm/smp.h>
@@ -58,11 +60,11 @@ static int dca_enabled_in_bios(struct pci_dev *pdev)
 {
 	/* CPUID level 9 returns DCA configuration */
 	/* Bit 0 indicates DCA enabled by the BIOS */
-	unsigned long cpuid_level_9;
+	u32 eax;
 	int res;
 
-	cpuid_level_9 = cpuid_eax(9);
-	res = test_bit(0, &cpuid_level_9);
+	eax = cpuid_eax(CPUID_DCA_LEAF);
+	res = eax & BIT(0);
 	if (!res)
 		dev_dbg(&pdev->dev, "DCA is disabled in BIOS\n");