Re: [PATCH v3 4/9] drm/xe/hwmon: expose pwm[1-3]

["Purkait, Soham" <soham.purkait@intel.com>]

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Hi Karthik,

On 16-10-2026 00:37, Karthik Poosa wrote:
> Expose pwm[1-3] fan duty attributes through hwmon.
>
> This enables reading and writing user PWM values (0..255) for each
> available fan channel.
>
> Update Xe hwmon ABI documentation for pwm[1-3].
>
> This sysfs node can be used for manual control of fan speed,
> irrespective of fan curve.
>
> v2:
>   - Use xe helpers for dmesg logs.
>   - Avoid using hwmon->num_fans to get fan count in
>     xe_hwmon_pwm_is_visible().
>
> v3:
>   - Set PWM directly through the user table; avoid initializing it from the
>     stock table. (Soham)
>   - Move the unused xe_hwmon_activate_user_fan_table() to the subsequent
>     patch.
>   - Fail pwmN reads when no value has been written, rather than activating
>     the user table from the stock table.
>   - Define MIN_FAN_CONTROL_POINTS as 2.
>   - Use MIN_FAN_CONTROL_POINTS for PWM configuration. (Soham)
>   - Use batched writes for configuring fan control points when setting pwmN.
>   - Add and rephrase couple debug logs.
>   - Update the hwmon documentation.
>
> Signed-off-by: Karthik Poosa<karthik.poosa@intel.com>
> Assisted-by: LLM
> ---
>   .../ABI/testing/sysfs-driver-intel-xe-hwmon   |   9 +
>   drivers/gpu/drm/xe/xe_hwmon.c                 | 170 ++++++++++++++++++
>   drivers/gpu/drm/xe/xe_pcode_api.h             |   3 +
>   3 files changed, 182 insertions(+)
>
> diff --git a/Documentation/ABI/testing/sysfs-driver-intel-xe-hwmon b/Documentation/ABI/testing/sysfs-driver-intel-xe-hwmon
> index 5ee68aefa485..ce17e9ca3ed8 100644
> --- a/Documentation/ABI/testing/sysfs-driver-intel-xe-hwmon
> +++ b/Documentation/ABI/testing/sysfs-driver-intel-xe-hwmon
> @@ -321,3 +321,12 @@ Description:	RW. Package burst power limit interval (Tau in PL2/Tau) in
>   		milliseconds over which sustained power is averaged.
>   
>   		Only supported for particular Intel Xe graphics platforms.
> +
> +What:           /sys/bus/pci/drivers/xe/.../hwmon/hwmon<i>/pwm[1-3]
> +Date:           October 2026
> +KernelVersion:  7.3
> +Contact:intel-xe@lists.freedesktop.org
> +Description:    RW. Target fan PWM duty value in the range 0..255. 0 is zero
> +                fan speed and 255 is 100% fan speed.
> +
> +                Only supported for particular Intel Xe graphics platforms.
Use tab indentation after the field labels.
> diff --git a/drivers/gpu/drm/xe/xe_hwmon.c b/drivers/gpu/drm/xe/xe_hwmon.c
> index 32016c5d4770..a86ed741feb3 100644
> --- a/drivers/gpu/drm/xe/xe_hwmon.c
> +++ b/drivers/gpu/drm/xe/xe_hwmon.c
> @@ -8,6 +8,7 @@
>   #include <linux/jiffies.h>
>   #include <linux/types.h>
>   #include <linux/units.h>
> +#include <linux/delay.h>
Is this header required ?
>   
>   #include <drm/drm_managed.h>
>   #include "regs/xe_gt_regs.h"
> @@ -153,6 +154,9 @@ enum fan_table_type {
>   /* Maximum number of fan control points supported by each fan. */
>   #define MAX_FAN_CONTROL_POINTS	(10)
>   
> +/* Minimum number of points required for a user fan table. */
> +#define MIN_FAN_CONTROL_POINTS  (2)
Use tab indentation.
> +
>   /* Fan control point index: bit31 selects fan table type; bits30:0 control point index. */
>   #define FCP_INDEX(FAN_TABLE_TYPE, POINT_NUM) (((FAN_TABLE_TYPE) << 31) | \
>   						((POINT_NUM) & REG_GENMASK(30, 0)))
> @@ -913,6 +917,7 @@ static const struct hwmon_channel_info * const hwmon_info[] = {
>   	HWMON_CHANNEL_INFO(energy, HWMON_E_INPUT | HWMON_E_LABEL, HWMON_E_INPUT | HWMON_E_LABEL),
>   	HWMON_CHANNEL_INFO(fan, HWMON_F_INPUT | HWMON_F_MAX, HWMON_F_INPUT | HWMON_F_MAX,
>   			   HWMON_F_INPUT | HWMON_F_MAX),
> +	HWMON_CHANNEL_INFO(pwm, HWMON_PWM_INPUT, HWMON_PWM_INPUT, HWMON_PWM_INPUT),
>   	NULL
>   };
>   
> @@ -1154,6 +1159,89 @@ static int xe_hwmon_get_fan_enable_mask(struct xe_hwmon *hwmon)
>   	return 0;
>   }
>   
> +static int xe_hwmon_get_fan_point_count(struct xe_hwmon *hwmon, u8 fan, u32 *point_count,
> +					enum fan_table_type table_type)
> +{
> +	int ret;
> +
> +	ret = xe_hwmon_pcode_read_fan_control(hwmon,
> +					      (table_type == USER_FAN_TABLE) ?
> +					      FSC_READ_USER_FAN_CONTROL_POINTS :
> +					      FSC_READ_STOCK_FAN_CONTROL_POINTS,
> +					      fan, point_count);
> +	if (ret) {
> +		xe_err(hwmon->xe, "failed to read fan %d %s point count, ret=%d\n", fan,
> +		       (table_type == USER_FAN_TABLE) ? "user" : "stock", ret);
> +		return ret;
> +	}
> +
> +	if (*point_count > MAX_FAN_CONTROL_POINTS) {
> +		xe_err(hwmon->xe, "fan %d %s point count %u exceeds max %u\n", fan,
> +		       (table_type == USER_FAN_TABLE) ? "user" : "stock", *point_count,
> +		       MAX_FAN_CONTROL_POINTS);
> +		return -EINVAL;
> +	}
> +
> +	return 0;
> +}
> +
> +/* Temperature to set when setting the fan PWM with pwmN. */
> +#define FIXED_PWM_TEMP	(1)
> +
> +static int xe_hwmon_set_user_fan_pwm(struct xe_hwmon *hwmon, u8 fan, u8 pwm)
> +{
> +	struct xe_hwmon_fan_info *fi = &hwmon->fi[fan];
> +	struct xe_pcode_write writes[MIN_FAN_CONTROL_POINTS + 1];
> +	u32 point_count = 0;
> +	u8 clamped_pwm;
> +	int ret, i;
> +
> +	pwm = DIV_ROUND_CLOSEST(pwm * 100, U8_MAX);
> +	clamped_pwm = max_t(u8, pwm, min_t(u32, fi->min_pwm, U8_MAX));
Is clamped_pwm and  fi->min_pwm in percentage ? If so use 100 *instead 
of* U8_MAX to be the max value.
> +
> +	/*
> +	 * Set the first fan control point in the user table to the clamped PWM value.
> +	 * Use only the first fan control point for setting the PWM value.
It says "only the first fan control point" but the loop end up writing 2 
points.
> +	 */
> +
> +	for (i = 0; i < MIN_FAN_CONTROL_POINTS; i++) {
> +		writes[i].mbox = PCODE_MBOX(FAN_SPEED_CONTROL, FSC_WRITE_FAN_TABLE, fan);
> +		writes[i].data = FIELD_PREP(FAN_CONTROL_POINT_TEMP_MASK, FIXED_PWM_TEMP + (i)) |
> +					    FIELD_PREP(FAN_CONTROL_POINT_SPEED_MASK, clamped_pwm);
> +		xe_dbg(hwmon->xe, "prepared fan control point %d with temp=%d, speed=%u\n", i,
> +		       FIXED_PWM_TEMP + (i), clamped_pwm);
> +	}
> +
> +	writes[i].mbox = PCODE_MBOX(FAN_SPEED_CONTROL, FSC_WRITE_NUM_FAN_CONTROL_POINTS, fan);
> +	writes[i].data = MIN_FAN_CONTROL_POINTS;
> +	ret = xe_pcode_write_batch(xe_device_get_root_tile(hwmon->xe), writes, ARRAY_SIZE(writes));
> +	if (ret) {
> +		xe_err(hwmon->xe, "failed to write pwm %d for fan %d, ret=%d\n", pwm, fan, ret);
"pwm" has been reassigned to a percentage by this point, so either print 
the original 0–255 value (keep it in a separate variable) or label this 
one as a percentage.
> +		return ret;
> +	}
> +	xe_dbg(hwmon->xe, "applied fixed pwm %u for fan %d\n", clamped_pwm, fan);
> +
> +	/* Verify if the fan points are set */
> +	ret = xe_hwmon_get_fan_point_count(hwmon, fan, &point_count, USER_FAN_TABLE);
> +	if (ret && point_count == 0) {
On failure point_count is already 0, so && point_count == 0 seems to be 
redundant.
Instead could this be more usable :
if (ret || point_count != MIN_FAN_CONTROL_POINTS),  if the valid write 
needed to be checked ?

> +		xe_err(hwmon->xe, "pwm set verify failed for fan %d, ret=%d, point count=%u\n", fan,
> +		       ret, point_count);
> +		return ret;
> +	}
> +
> +	/* Update the user fan table cache. */
> +	for (i = 0; i < MIN_FAN_CONTROL_POINTS; i++) {
> +		fi->fan_table[USER_FAN_TABLE].fcp[i].temp = FIXED_PWM_TEMP + (i);
Drop the parentheses around i: FIXED_PWM_TEMP + i.
> +		fi->fan_table[USER_FAN_TABLE].fcp[i].speed = clamped_pwm;
> +		xe_dbg(hwmon->xe, "fan %d user table cache point %d with temp=%d, speed=%u\n", fan,
> +		       i, fi->fan_table[USER_FAN_TABLE].fcp[i].temp,
> +			  fi->fan_table[USER_FAN_TABLE].fcp[i].speed);
The arguments don't align under the opening (.
> +	}
> +	fi->fan_table[USER_FAN_TABLE].point_count = MIN_FAN_CONTROL_POINTS;
> +
> +	return 0;
> +}
> +
>   static int xe_hwmon_read_fan_control_info(struct xe_hwmon *hwmon)
>   {
>   	struct xe_tile *root_tile = xe_device_get_root_tile(hwmon->xe);
> @@ -1774,6 +1862,20 @@ xe_hwmon_fan_is_visible(struct xe_hwmon *hwmon, u32 attr, int channel)
>   	}
>   }
>   
> +static umode_t
> +xe_hwmon_pwm_is_visible(struct xe_hwmon *hwmon, u32 attr, int channel)
> +{
> +	if (!hwmon->xe->info.has_fan_control || !IS_FAN_ENABLED(channel))
> +		return 0;
> +
> +	switch (attr) {
> +	case hwmon_pwm_input:
> +		return 0644;
> +	default:
> +		return 0;
> +	}
> +}
> +
>   static int
>   xe_hwmon_fan_input_read(struct xe_hwmon *hwmon, int channel, long *val)
>   {
> @@ -1828,6 +1930,67 @@ xe_hwmon_fan_read(struct xe_hwmon *hwmon, u32 attr, int channel, long *val)
>   	}
>   }
>   
> +static int
> +xe_hwmon_pwm_read(struct xe_hwmon *hwmon, u32 attr, int channel, long *val)
> +{
> +	struct xe_hwmon_fan_info *fi;
> +	int ret = 0;
> +
> +	if (channel < 0 || channel >= FAN_MAX)
Add a short xe_dbg/xe_warn before these -EINVAL returns for clarity.
> +		return -EINVAL;
> +
> +	mutex_lock(&hwmon->hwmon_lock);
> +
> +	fi = &hwmon->fi[channel];
> +
> +	switch (attr) {
> +	case hwmon_pwm_input:
> +		/* Check if user fan table is set else activate it.*/
Where does it activate ? Use space before */.
> +		if (!fi->fan_table[USER_FAN_TABLE].point_count) {
> +			xe_warn(hwmon->xe, "pwm not set for fan %d\n", channel);
> +			ret = -ENXIO;
> +			goto unlock;
> +		}
> +		*val = DIV_ROUND_CLOSEST(fi->fan_table[USER_FAN_TABLE].fcp[0].speed * U8_MAX, 100);
The 0–255 <-> percentage round-trip is lossy for small values; Better to 
add a one-line note since the ABI says a full 0–255 range.
> +		xe_dbg(hwmon->xe, "pwm read for fan %d: %ld\n", channel, *val);
> +		break;
> +	default:
> +		ret = -EOPNOTSUPP;
> +		break;
> +	}
> +
> +unlock:
> +	mutex_unlock(&hwmon->hwmon_lock);
> +	return ret;
> +}
> +
> +static int
> +xe_hwmon_pwm_write(struct xe_hwmon *hwmon, u32 attr, int channel, long val)
> +{
> +	int ret = 0;
> +
> +	if (channel < 0 || channel >= FAN_MAX)

Add a short xe_dbg/xe_warn before these -EINVAL returns for clarity.


Regards,
Soham
> +		return -EINVAL;
> +
> +	mutex_lock(&hwmon->hwmon_lock);
> +
> +	switch (attr) {
> +	case hwmon_pwm_input:
> +		if (val < 0 || val > U8_MAX) {
> +			ret = -EINVAL;
> +			break;
> +		}
> +		ret = xe_hwmon_set_user_fan_pwm(hwmon, channel, (u8)val);
> +		break;
> +	default:
> +		ret = -EOPNOTSUPP;
> +		break;
> +	}
> +	mutex_unlock(&hwmon->hwmon_lock);
> +
> +	return ret;
> +}
> +
>   static umode_t
>   xe_hwmon_is_visible(const void *drvdata, enum hwmon_sensor_types type,
>   		    u32 attr, int channel)
> @@ -1854,6 +2017,9 @@ xe_hwmon_is_visible(const void *drvdata, enum hwmon_sensor_types type,
>   	case hwmon_fan:
>   		ret = xe_hwmon_fan_is_visible(hwmon, attr, channel);
>   		break;
> +	case hwmon_pwm:
> +		ret = xe_hwmon_pwm_is_visible(hwmon, attr, channel);
> +		break;
>   	default:
>   		ret = 0;
>   		break;
> @@ -1883,6 +2049,8 @@ xe_hwmon_read(struct device *dev, enum hwmon_sensor_types type, u32 attr,
>   		return xe_hwmon_energy_read(hwmon, attr, channel, val);
>   	case hwmon_fan:
>   		return xe_hwmon_fan_read(hwmon, attr, channel, val);
> +	case hwmon_pwm:
> +		return xe_hwmon_pwm_read(hwmon, attr, channel, val);
>   	default:
>   		return -EOPNOTSUPP;
>   	}
> @@ -1901,6 +2069,8 @@ xe_hwmon_write(struct device *dev, enum hwmon_sensor_types type, u32 attr,
>   		return xe_hwmon_power_write(hwmon, attr, channel, val);
>   	case hwmon_curr:
>   		return xe_hwmon_curr_write(hwmon, attr, channel, val);
> +	case hwmon_pwm:
> +		return xe_hwmon_pwm_write(hwmon, attr, channel, val);
>   	default:
>   		return -EOPNOTSUPP;
>   	}
> diff --git a/drivers/gpu/drm/xe/xe_pcode_api.h b/drivers/gpu/drm/xe/xe_pcode_api.h
> index 32bac74c4281..80642bee0ac8 100644
> --- a/drivers/gpu/drm/xe/xe_pcode_api.h
> +++ b/drivers/gpu/drm/xe/xe_pcode_api.h
> @@ -82,9 +82,12 @@
>   #define     PCODE_MBOX_DOMAIN_HBM		0x2
>   
>   #define   FAN_SPEED_CONTROL			0x7D
> +#define     FSC_WRITE_NUM_FAN_CONTROL_POINTS	0x0
> +#define     FSC_WRITE_FAN_TABLE			0x1
>   #define     FSC_READ_MAX_FAN_RPS        0x3
>   #define     FSC_READ_NUM_FANS			0x4
>   #define     FSC_READ_STOCK_FAN_CONTROL_POINTS	0x5
> +#define     FSC_READ_USER_FAN_CONTROL_POINTS	0x6
>   #define     FSC_READ_FAN_TABLE			0x7
>   #define     FAN_CONTROL_POINT_TEMP_MASK		REG_GENMASK(7, 0)
>   #define     FAN_CONTROL_POINT_SPEED_MASK	REG_GENMASK(15, 8)

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