platform/x86: intel_pmc_core: Decode Snoop / Non Snoop LTR

The LTR values follow PCIE LTR encoding format and can be decoded as per
https://pcisig.com/sites/default/files/specification_documents/ECN_LatencyTolnReporting_14Aug08.pdf

This adds support to translate the raw LTR values as read from the PMC
to meaningful values in nanosecond units of time.
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/x86/intel_pmc_core.c

@@ -12,6 +12,7 @@
 #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt
 
 #include <linux/acpi.h>
+#include <linux/bitfield.h>
 #include <linux/debugfs.h>
 #include <linux/delay.h>
 #include <linux/io.h>
@@ -638,15 +639,72 @@ static int pmc_core_slps0_dbg_show(struct seq_file *s, void *unused)
 }
 DEFINE_SHOW_ATTRIBUTE(pmc_core_slps0_dbg);
 
+static u32 convert_ltr_scale(u32 val)
+{
+	/*
+	 * As per PCIE specification supporting document
+	 * ECN_LatencyTolnReporting_14Aug08.pdf the Latency
+	 * Tolerance Reporting data payload is encoded in a
+	 * 3 bit scale and 10 bit value fields. Values are
+	 * multiplied by the indicated scale to yield an absolute time
+	 * value, expressible in a range from 1 nanosecond to
+	 * 2^25*(2^10-1) = 34,326,183,936 nanoseconds.
+	 *
+	 * scale encoding is as follows:
+	 *
+	 * ----------------------------------------------
+	 * |scale factor	|	Multiplier (ns)	|
+	 * ----------------------------------------------
+	 * |	0		|	1		|
+	 * |	1		|	32		|
+	 * |	2		|	1024		|
+	 * |	3		|	32768		|
+	 * |	4		|	1048576		|
+	 * |	5		|	33554432	|
+	 * |	6		|	Invalid		|
+	 * |	7		|	Invalid		|
+	 * ----------------------------------------------
+	 */
+	if (val > 5) {
+		pr_warn("Invalid LTR scale factor.\n");
+		return 0;
+	}
+
+	return 1U << (5 * val);
+}
+
 static int pmc_core_ltr_show(struct seq_file *s, void *unused)
 {
 	struct pmc_dev *pmcdev = s->private;
 	const struct pmc_bit_map *map = pmcdev->map->ltr_show_sts;
+	u64 decoded_snoop_ltr, decoded_non_snoop_ltr;
+	u32 ltr_raw_data, scale, val;
+	u16 snoop_ltr, nonsnoop_ltr;
 	int index;
 
 	for (index = 0; map[index].name ; index++) {
-		seq_printf(s, "%-32s\tRAW LTR: 0x%x\n", map[index].name,
-			   pmc_core_reg_read(pmcdev, map[index].bit_mask));
+		decoded_snoop_ltr = decoded_non_snoop_ltr = 0;
+		ltr_raw_data = pmc_core_reg_read(pmcdev,
+						 map[index].bit_mask);
+		snoop_ltr = ltr_raw_data & ~MTPMC_MASK;
+		nonsnoop_ltr = (ltr_raw_data >> 0x10) & ~MTPMC_MASK;
+
+		if (FIELD_GET(LTR_REQ_NONSNOOP, ltr_raw_data)) {
+			scale = FIELD_GET(LTR_DECODED_SCALE, nonsnoop_ltr);
+			val = FIELD_GET(LTR_DECODED_VAL, nonsnoop_ltr);
+			decoded_non_snoop_ltr = val * convert_ltr_scale(scale);
+		}
+
+		if (FIELD_GET(LTR_REQ_SNOOP, ltr_raw_data)) {
+			scale = FIELD_GET(LTR_DECODED_SCALE, snoop_ltr);
+			val = FIELD_GET(LTR_DECODED_VAL, snoop_ltr);
+			decoded_snoop_ltr = val * convert_ltr_scale(scale);
+		}
+
+		seq_printf(s, "%-32s\tLTR: RAW: 0x%-16x\tNon-Snoop(ns): %-16llu\tSnoop(ns): %-16llu\n",
+			   map[index].name, ltr_raw_data,
+			   decoded_non_snoop_ltr,
+			   decoded_snoop_ltr);
 	}
 	return 0;
 }

drivers/platform/x86/intel_pmc_core.h

@@ -12,6 +12,8 @@
 #ifndef PMC_CORE_H
 #define PMC_CORE_H
 
+#include <linux/bits.h>
+
 #define PMC_BASE_ADDR_DEFAULT			0xFE000000
 
 /* Sunrise Point Power Management Controller PCI Device ID */
@@ -169,6 +171,11 @@ enum ppfear_regs {
 #define CNP_PMC_LTR_EMMC			0x1BF4
 #define CNP_PMC_LTR_UFSX2			0x1BF8
 
+#define LTR_DECODED_VAL				GENMASK(9, 0)
+#define LTR_DECODED_SCALE			GENMASK(12, 10)
+#define LTR_REQ_SNOOP				BIT(15)
+#define LTR_REQ_NONSNOOP			BIT(31)
+
 struct pmc_bit_map {
 	const char *name;
 	u32 bit_mask;