Re: [PATCH v2 7/9] drm/xe/hwmon: Add kernel-doc for fan control

["Poosa, Karthik" <karthik.poosa@intel.com>]

On 04-09-2026 09:32, Purkait, Soham wrote:
> HI Karthik,
>
> On 17-07-2026 09:47, Karthik Poosa wrote:
>> Add kernel-doc for xe hwmon fan control and describe the fan control
>> model built around firmware stock tables and driver-managed user tables.
>>
>> Document the exposed sysfs files for fan speed, maximum speed, pwm
>> control, pwm mode selection, and per-point fan curve temperature/PWM
>> programming.
>>
>> This makes the hwmon fan control userspace interface easier to discover
>> and understand.
>>
>> Signed-off-by: Karthik Poosa <karthik.poosa@intel.com>
>> Assisted-by: Codex:gpt-5-4
>> ---
>>   drivers/gpu/drm/xe/xe_hwmon.c | 43 +++++++++++++++++++++++++++++++++++
>>   1 file changed, 43 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/xe/xe_hwmon.c 
>> b/drivers/gpu/drm/xe/xe_hwmon.c
>> index a3ed139ad446..770f07fb6511 100644
>> --- a/drivers/gpu/drm/xe/xe_hwmon.c
>> +++ b/drivers/gpu/drm/xe/xe_hwmon.c
>> @@ -123,6 +123,49 @@ struct xe_hwmon_energy_info {
>>       long accum_energy;
>>   };
>>   +/**
>> + * DOC: Xe fan control
>> + *
>> + * Xe fan control is exposed through the hwmon pwm and fan 
>> interfaces when the
>> + * platform advertises PCODE-backed fan management support.
>> + *
>> + * The implementation tracks two fan tables per fan:
>> + *
>> + * - A stock table read from firmware through PCODE.
>> + * - A user table cached in the driver and programmed back through 
>> PCODE.
>> + *
>> + * The pwmN_enable sysfs mode selects how those tables are used:
>> + *
>> + * - ``XE_FAN_PWM_AUTO_STOCK_TABLE`` restores automatic control 
>> using the stock
>> + *   firmware table.
>> + * - ``XE_FAN_PWM_MANUAL_USER_TABLE`` enables the user table for 
>> manual control.
>> + * - ``XE_FAN_PWM_FULL_SPEED`` reuses the user table path but 
>> programs every
>> + *   point to 100 percent duty cycle as a full-speed override.
>> + *
>> + * The fan-control sysfs files are:
>> + *
>> + * - ``fanN_input`` reports the measured fan speed in RPM.
>> + * - ``fanN_max`` reports the maximum supported fan speed in RPM.
>> + * - ``pwmN`` reads or sets the manual PWM duty cycle in the hwmon 
>> 0..255
>> + *   range. Manual writes are accepted only while ``pwmN_enable`` is 
>> set to
>> + *   ``XE_FAN_PWM_MANUAL_USER_TABLE``.
> Could you please double check this claim ? Seems like in 
> XE_FAN_PWM_FULL_SPEED mode of pwmN_enable also accepts the manual write.

you are right,

we shall restrict pwm writes for FULL speed mode also.

current we are checking only for auto mode in xe_hwmon_set_user_fan_pwm()

1206         if (fi->pwm_enable_mode == XE_FAN_PWM_AUTO_STOCK_TABLE) {
1207                 xe_dbg(hwmon->xe, "fan %d manual table is not 
active, cannot set pwm\n", fan);
1208                 return -EINVAL;
1209         }

>> + * - ``pwmN_enable`` selects stock automatic mode, manual user-table 
>> mode, or
>> + *   full-speed override.
>> + * - ``pwmN_auto_pointM_temp`` exposes the temperature threshold for 
>> user-table
>> + *   point ``M`` in millidegrees Celsius.
>> + * - ``pwmN_auto_pointM_pwm`` exposes the PWM value for user-table 
>> point ``M``
>> + *   in the hwmon 0..255 range.
>
> Is it always user-table point ? What happens when mode is set to 
> XE_FAN_PWM_AUTO_STOCK_TABLE ?

1. Yes it is always user table point, stock table is read only from 
pcode mailbox.

2. fan curve point writes are allowed only in manual user mode,

see, xe_hwmon_pwm_auto_point_temp_store()

1388         if (fi->pwm_enable_mode != XE_FAN_PWM_MANUAL_USER_TABLE) {
1389                 drm_err(&hwmon->xe->drm,
1390                         "pwm%d_enable not in manual mode; cannot 
update temp point %d\n",
1391                         fan, point);
1392                 return -EINVAL;
1393         }

xe_hwmon_pwm_auto_point_pwm_store()

1492         if (fi->pwm_enable_mode != XE_FAN_PWM_MANUAL_USER_TABLE) {
1493                 drm_err(&hwmon->xe->drm,
1494                         "pwm%d_enable is not in manual user mode, 
cannot update pwm point %d\n",
1495                         fan, point);
1496                 return -EINVAL;
1497         }

>
> Thanks,
> Soham
>
>> + *
>> + * Writes to pwmN_auto_pointM_temp and pwmN_auto_pointM_pwm update 
>> the cached
>> + * user table entries. The driver commits the full user table once 
>> the last
>> + * point has both temperature and PWM values, which keeps 
>> intermediate sysfs
>> + * writes from pushing partially updated curves to firmware.
>> + *
>> + * Writes to pwmN provide a constant manual duty cycle by rewriting 
>> every point
>> + * in the active user table to the same PWM value, clamped against 
>> the minimum
>> + * duty cycle reported by firmware for that fan.
>> + */
>> +
>>   enum xe_fan_pwm_enable_mode {
>>       /** @XE_FAN_PWM_FULL_SPEED: force all user table points to full 
>> speed */
>>       XE_FAN_PWM_FULL_SPEED = 0,