drm/i915/hwmon: Add HWMON current voltage support

Use i915 HWMON subsystem to display current input voltage.

v2:
  - Updated date and kernel version in feature description
  - Fixed review comments (Ashutosh)
v3: Use macro HWMON_CHANNEL_INFO to define hwmon channel (Guenter)
v4:
  - Fixed review comments (Ashutosh)
  - Use hwm_ prefix for static functions (Ashutosh)
v5: Added unit of voltage as millivolts (Ashutosh)
v6: KernelVersion: 6.2, Date: February 2023 in doc (Tvrtko)
v7: Change contact to intel-gfx (Rodrigo)
    GEN12_RPSTAT1 is available for all Gen12+ (Andi)
    Added Documentation/ABI/testing/sysfs-driver-intel-i915-hwmon
    to MAINTAINERS

Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Riana Tauro <riana.tauro@intel.com>
Signed-off-by: Badal Nilawar <badal.nilawar@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Acked-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Anshuman Gupta <anshuman.gupta@intel.com>
Signed-off-by: Anshuman Gupta <anshuman.gupta@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20221013154526.2105579-3-ashutosh.dixit@intel.com

Documentation/ABI/testing/sysfs-driver-intel-i915-hwmon

+What:		/sys/devices/.../hwmon/hwmon<i>/in0_input
+Date:		February 2023
+KernelVersion:	6.2
+Contact:	intel-gfx@lists.freedesktop.org
+Description:	RO. Current Voltage in millivolt.
+
+		Only supported for particular Intel i915 graphics platforms.

MAINTAINERS

@@ -10140,6 +10140,7 @@ Q:	http://patchwork.freedesktop.org/project/intel-gfx/
 B:	https://gitlab.freedesktop.org/drm/intel/-/wikis/How-to-file-i915-bugs
 C:	irc://irc.oftc.net/intel-gfx
 T:	git git://anongit.freedesktop.org/drm-intel
+F:	Documentation/ABI/testing/sysfs-driver-intel-i915-hwmon
 F:	Documentation/gpu/i915.rst
 F:	drivers/gpu/drm/i915/
 F:	include/drm/i915*

drivers/gpu/drm/i915/gt/intel_gt_regs.h

@@ -1516,6 +1516,9 @@
 #define VLV_RENDER_C0_COUNT			_MMIO(0x138118)
 #define VLV_MEDIA_C0_COUNT			_MMIO(0x13811c)
 
+#define GEN12_RPSTAT1				_MMIO(0x1381b4)
+#define   GEN12_VOLTAGE_MASK			REG_GENMASK(10, 0)
+
 #define GEN11_GT_INTR_DW(x)			_MMIO(0x190018 + ((x) * 4))
 #define   GEN11_CSME				(31)
 #define   GEN11_GUNIT				(28)

drivers/gpu/drm/i915/i915_hwmon.c

@@ -11,8 +11,16 @@
 #include "i915_hwmon.h"
 #include "i915_reg.h"
 #include "intel_mchbar_regs.h"
+#include "gt/intel_gt_regs.h"
+
+/*
+ * SF_* - scale factors for particular quantities according to hwmon spec.
+ * - voltage  - millivolts
+ */
+#define SF_VOLTAGE	1000
 
 struct hwm_reg {
+	i915_reg_t gt_perf_status;
 };
 
 struct hwm_drvdata {
@@ -29,14 +37,51 @@ struct i915_hwmon {
 };
 
 static const struct hwmon_channel_info *hwm_info[] = {
+	HWMON_CHANNEL_INFO(in, HWMON_I_INPUT),
 	NULL
 };
 
+static umode_t
+hwm_in_is_visible(const struct hwm_drvdata *ddat, u32 attr)
+{
+	struct drm_i915_private *i915 = ddat->uncore->i915;
+
+	switch (attr) {
+	case hwmon_in_input:
+		return IS_DG1(i915) || IS_DG2(i915) ? 0444 : 0;
+	default:
+		return 0;
+	}
+}
+
+static int
+hwm_in_read(struct hwm_drvdata *ddat, u32 attr, long *val)
+{
+	struct i915_hwmon *hwmon = ddat->hwmon;
+	intel_wakeref_t wakeref;
+	u32 reg_value;
+
+	switch (attr) {
+	case hwmon_in_input:
+		with_intel_runtime_pm(ddat->uncore->rpm, wakeref)
+			reg_value = intel_uncore_read(ddat->uncore, hwmon->rg.gt_perf_status);
+		/* HW register value in units of 2.5 millivolt */
+		*val = DIV_ROUND_CLOSEST(REG_FIELD_GET(GEN12_VOLTAGE_MASK, reg_value) * 25, 10);
+		return 0;
+	default:
+		return -EOPNOTSUPP;
+	}
+}
+
 static umode_t
 hwm_is_visible(const void *drvdata, enum hwmon_sensor_types type,
 	       u32 attr, int channel)
 {
+	struct hwm_drvdata *ddat = (struct hwm_drvdata *)drvdata;
+
 	switch (type) {
+	case hwmon_in:
+		return hwm_in_is_visible(ddat, attr);
 	default:
 		return 0;
 	}
@@ -46,7 +91,11 @@ static int
 hwm_read(struct device *dev, enum hwmon_sensor_types type, u32 attr,
 	 int channel, long *val)
 {
+	struct hwm_drvdata *ddat = dev_get_drvdata(dev);
+
 	switch (type) {
+	case hwmon_in:
+		return hwm_in_read(ddat, attr, val);
 	default:
 		return -EOPNOTSUPP;
 	}
@@ -76,6 +125,10 @@ static const struct hwmon_chip_info hwm_chip_info = {
 static void
 hwm_get_preregistration_info(struct drm_i915_private *i915)
 {
+	struct i915_hwmon *hwmon = i915->hwmon;
+
+	/* Available for all Gen12+/dGfx */
+	hwmon->rg.gt_perf_status = GEN12_RPSTAT1;
 }
 
 void i915_hwmon_register(struct drm_i915_private *i915)