On Mon, Nov 08, 2021 at 09:47:54AM +0100, Peter Zijlstra wrote:

On Fri, Nov 05, 2021 at 06:33:08PM -0700, Ricardo Neri wrote:

quoted

+static __init int hfi_parse_features(void)
+{
+	unsigned int nr_capabilities, reg;
+

quoted

+	/*
+	 * If we are here we know that CPUID_HFI_LEAF exists. Parse the
+	 * supported capabilities and the size of the HFI table.
+	 */
+	reg = cpuid_edx(CPUID_HFI_LEAF);
+
+	hfi_features.capabilities = reg & HFI_CAPABILITIES_MASK;
+	if (!(hfi_features.capabilities & HFI_CAPABILITIES_PERFORMANCE)) {
+		pr_err("Performance reporting not supported! Not using HFI\n");
+		return -ENODEV;
+	}
+
+	/* The number of 4KB pages required by the table */
+	hfi_features.nr_table_pages = ((reg & CPUID_HFI_TABLE_SIZE_MASK) >>
+				      CPUID_HFI_TABLE_SIZE_SHIFT) + 1;
+

quoted

+/* Hardware Feedback Interface Enumeration */
+#define CPUID_HFI_LEAF			6
+#define CPUID_HFI_CAP_MASK		0xff
+#define CPUID_HFI_TABLE_SIZE_MASK	0x0f00
+#define CPUID_HFI_TABLE_SIZE_SHIFT	8
+#define CPUID_HFI_CPU_INDEX_MASK	0xffff0000

Also, *if* you're going to do something like this, then at least write
out the masks in full so you can easily see how they relate. The above
is crap.

quoted

+#define CPUID_HFI_CPU_INDEX_SHIFT	16
+
+/* Hardware Feedback Interface Pointer */
+#define HFI_PTR_VALID_BIT		BIT(0)
+#define HFI_PTR_ADDR_SHIFT		12
+
+/* Hardware Feedback Interface Configuration */
+#define HFI_CONFIG_ENABLE_BIT		BIT(0)
+
+/* Hardware Feedback Interface Capabilities */
+#define HFI_CAPABILITIES_MASK		0xff
+#define HFI_CAPABILITIES_NR		8
+#define HFI_CAPABILITIES_PERFORMANCE	BIT(0)
+#define HFI_CAPABILITIES_ENERGY_EFF	BIT(1)

So personally I prefer a bitfield union a-la cpuid10_eax, cpuid10_ebx
cpuid10_edx etc.. Barring that, the above can also be written more
concise using FIELD_GET() from bitfields.

union cpuid6_edx {
	struct {
		unsigned int capabilities :  8;
		unsigned int table_size   :  4;
		unsigned int __reserved   :  4;
		unsigned int cpu_index    : 16;
	};
	unsigned int full;
};

Sure Peter. This looks more readable. I'll implement it like this.

Thanks and BR,
Ricardo