drm/xe/hwmon: Add helpers to validate thermal sensor readings

Add mmio_temp_valid() and mbx_temp_valid() to check whether a temperature
sensor reading is valid. An MMIO value of 0xFFFFFFFF or a mailbox value of
0xFF indicates the sensor is unavailable.

Gate these checks behind has_temp_sentinel, enabled on CRI currently.

Signed-off-by: Karthik Poosa <karthik.poosa@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patch.msgid.link/20261015071434.1063785-5-karthik.poosa@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Matthew Brost <matthew.brost@intel.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

4 files changed, 32 insertions, 0 deletions

diff --git a/drivers/gpu/drm/xe/xe_device_types.h b/drivers/gpu/drm/xe/xe_device_types.h
index 41f703a87916..6d696c3ccd36 100644
--- a/drivers/gpu/drm/xe/xe_device_types.h
+++ b/drivers/gpu/drm/xe/xe_device_types.h
@@ -227,6 +227,8 @@ struct xe_device {
 		u8 has_sriov:1;
 		/** @info.has_sysctrl: Supports System Controller */
 		u8 has_sysctrl:1;
+		/** @info.has_temp_sentinel: Device has temperature-unavailable sentinels */
+		u8 has_temp_sentinel:1;
 		/** @info.has_usm: Device has unified shared memory support */
 		u8 has_usm:1;
 		/** @info.has_64bit_timestamp: Device supports 64-bit timestamps */
diff --git a/drivers/gpu/drm/xe/xe_hwmon.c b/drivers/gpu/drm/xe/xe_hwmon.c
index 7744e7e2e51b..13504a5f1b83 100644
--- a/drivers/gpu/drm/xe/xe_hwmon.c
+++ b/drivers/gpu/drm/xe/xe_hwmon.c
@@ -104,6 +104,9 @@ enum sensor_attr_power {
 /* Index of memory controller in READ_THERMAL_DATA output */
 #define TEMP_INDEX_MCTRL	2
 
+/* Mailbox sentinel reported for an unavailable temperature sensor */
+#define TEMP_MBX_INVALID	0xFF
+
 /* Mailbox temperature is sign-magnitude: bit 7 sign, bits 6:0 magnitude. */
 #define TEMP_MBX_SIGN		BIT(7)
 #define TEMP_MBX_MAG		GENMASK(6, 0)
@@ -854,6 +857,30 @@ static int xe_hwmon_pcode_read_thermal_info(struct xe_hwmon *hwmon)
 	return ret;
 }
 
+static inline bool mmio_temp_valid(const struct xe_hwmon *hwmon, u32 value)
+{
+	/*
+	 * On platforms lacking temperature sentinel support, a value of 0 is treated
+	 * as invalid. While 0°C is theoretically possible, it is highly unlikely for
+	 * a discrete GPU in normal environments, making it a reasonable fallback
+	 * indicator for invalid or uninitialized temperature readings.
+	 * All-ones is returned when the device is off the bus, so reject it too.
+	 */
+	if (value == U32_MAX)
+		return false;
+
+	return hwmon->xe->info.has_temp_sentinel || value != 0;
+}
+
+/* Mailbox temperature is sign-magnitude (bit 7 sign, bits 6:0 magnitude). */
+static inline bool mbx_temp_valid(const struct xe_hwmon *hwmon, u8 value)
+{
+	if (value == TEMP_MBX_INVALID)
+		return false;
+
+	return hwmon->xe->info.has_temp_sentinel || value != 0;
+}
+
 /* Decode an 8-bit sign-magnitude mailbox temperature to degrees Celsius. */
 static int mbx_temp_decode(u8 value)
 {
diff --git a/drivers/gpu/drm/xe/xe_pci.c b/drivers/gpu/drm/xe/xe_pci.c
index 50e4920e8e08..f785b5527376 100644
--- a/drivers/gpu/drm/xe/xe_pci.c
+++ b/drivers/gpu/drm/xe/xe_pci.c
@@ -486,6 +486,7 @@ static const struct xe_device_desc cri_desc = {
 	.has_soc_remapper_telem = true,
 	.has_sriov = true,
 	.has_sysctrl = true,
+	.has_temp_sentinel = true,
 	.max_gt_per_tile = 2,
 	MULTI_LRC_MASK,
 	.require_force_probe = true,
@@ -817,6 +818,7 @@ static int xe_info_init_early(struct xe_device *xe,
 	xe->info.has_sriov = xe_configfs_primary_gt_allowed(to_pci_dev(xe->drm.dev)) &&
 		desc->has_sriov;
 	xe->info.has_sysctrl = desc->has_sysctrl;
+	xe->info.has_temp_sentinel = desc->has_temp_sentinel;
 	xe->info.skip_guc_pc = desc->skip_guc_pc;
 	xe->info.skip_pcode = desc->skip_pcode;
 	xe->info.needs_scratch = desc->needs_scratch;
diff --git a/drivers/gpu/drm/xe/xe_pci_types.h b/drivers/gpu/drm/xe/xe_pci_types.h
index 448bbe5ba1d7..15eedac8467a 100644
--- a/drivers/gpu/drm/xe/xe_pci_types.h
+++ b/drivers/gpu/drm/xe/xe_pci_types.h
@@ -61,6 +61,7 @@ struct xe_device_desc {
 	u8 has_soc_remapper_telem:1;
 	u8 has_sriov:1;
 	u8 has_sysctrl:1;
+	u8 has_temp_sentinel:1;
 	u8 needs_scratch:1;
 	u8 skip_guc_pc:1;
 	u8 skip_pcode:1;