[PATCH v2] drm/xe/hwmon: Add SW clamp for power limits writes

[Karthik Poosa]

Clamp writes to power limits powerX_crit/currX_crit, powerX_cap,
powerX_max, to the maximum supported by the pcode mailbox
when sysfs-provided values exceed this limit.
Although the pcode already performs clamping, values beyond the pcode
mailbox's supported range get truncated, leading to incorrect
critical power settings.
This patch ensures proper clamping to prevent such truncation.

v2:
 - Address below review comments. (Riana)
 - Split comments into multiple sentences.
 - Use local variables for readability.
 - Add a debug log.
 - Use u64 instead of unsigned long.

Signed-off-by: Karthik Poosa <karthik.poosa at intel.com>
Fixes: 92d44a422d0d ("drm/xe/hwmon: Expose card reactive critical power")
Fixes: fb1b70607f73 ("drm/xe/hwmon: Expose power attributes")
---
 drivers/gpu/drm/xe/xe_hwmon.c | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/drivers/gpu/drm/xe/xe_hwmon.c b/drivers/gpu/drm/xe/xe_hwmon.c
index f08fc4377d25..768a942ab0e7 100644
--- a/drivers/gpu/drm/xe/xe_hwmon.c
+++ b/drivers/gpu/drm/xe/xe_hwmon.c
@@ -332,6 +332,7 @@ static int xe_hwmon_power_max_write(struct xe_hwmon *hwmon, u32 attr, int channe
 	int ret = 0;
 	u32 reg_val, max;
 	struct xe_reg rapl_limit;
+	u64 max_mbx_power_limit = 0;
 
 	mutex_lock(&hwmon->hwmon_lock);
 
@@ -356,6 +357,20 @@ static int xe_hwmon_power_max_write(struct xe_hwmon *hwmon, u32 attr, int channe
 		goto unlock;
 	}
 
+	/*
+	 * If the sysfs value exceeds the pcode mailbox cmd WRITE_PSYSGPU/PACKAGE_POWER_LIMIT
+	 * max supported value, clamp it to the command's max (U12.3 format).
+	 * This is to avoid truncation during reg_val calculation below and ensure the valid
+	 * power limit is sent for pcode which would clamp it to card-supported value.
+	 */
+	max_mbx_power_limit = ((PWR_LIM_VAL) >> hwmon->scl_shift_power) * SF_POWER;
+	if (value > max_mbx_power_limit) {
+		value = max_mbx_power_limit;
+		drm_dbg(&hwmon->xe->drm,
+			"Sysfs value for ch %d %s exceeds limit; clamped to supported maximum\n",
+			channel, PWR_ATTR_TO_STR(attr));
+	}
+
 	/* Computation in 64-bits to avoid overflow. Round to nearest. */
 	reg_val = DIV_ROUND_CLOSEST_ULL((u64)value << hwmon->scl_shift_power, SF_POWER);
 
@@ -739,9 +754,23 @@ static int xe_hwmon_power_curr_crit_write(struct xe_hwmon *hwmon, int channel,
 {
 	int ret;
 	u32 uval;
+	u64 max_crit_power_curr = 0;
 
 	mutex_lock(&hwmon->hwmon_lock);
 
+	/*
+	 * If the sysfs value exceeds the pcode mailbox cmd POWER_SETUP_SUBCOMMAND_WRITE_I1
+	 * max supported value, clamp it to the command's max (U10.6 format).
+	 * This is to avoid truncation during uval calculation below and ensure the valid power
+	 * limit is sent for pcode which would clamp it to card-supported value.
+	 */
+	max_crit_power_curr = (POWER_SETUP_I1_DATA_MASK >> POWER_SETUP_I1_SHIFT) * scale_factor;
+	if (value > max_crit_power_curr) {
+		value = max_crit_power_curr;
+		drm_dbg(&hwmon->xe->drm,
+			"Sysfs value for ch %d exceeds limit; clamped to supported maximum\n",
+			channel);
+	}
 	uval = DIV_ROUND_CLOSEST_ULL(value << POWER_SETUP_I1_SHIFT, scale_factor);
 	ret = xe_hwmon_pcode_write_i1(hwmon, uval);
 
-- 
2.25.1