Re: [RFC PATCH] drm/xe/hwmon: report a single fan for DG2 instead of two

[sashiko-bot@kernel.org]

> xe_hwmon_pcode_read_fan_control() currently hardcodes *uval = 2 when
> queried with FSC_READ_NUM_FANS on DG2. This causes fan2_input to be
> exposed via sysfs, but on the tested Arc A750 LE (DG2 G10, PCI ID
> 0x56a1) fan2_input reads 0 RPM permanently while fan1_input correctly
> reports ~800 RPM with both physical fan physically spinning.
> 
> The RPM is calculated delta-based from a tach pulse counter:
> 
>     rotations = (reg_val - fi->reg_val_prev) / 2;
> 
> so a constant-zero RPM means the register at offset 0x138170
> (BMG_FAN_2_SPEED) simply does not accumulate pulses on DG2 silicon.
> The i915 driver does not expose fan2 on DG2 at all -- it only maps
> PCU_PWM_FAN_SPEED (0x138140, identical to BMG_FAN_1_SPEED), consistent
> with the observation that only one fan tach register is wired on DG2.
> 
> Report a single fan for DG2 to keep the phantom fan2_input out of
> sysfs.  Battlemage paths are unchanged.
> 
> Tested on Arc A750 LE (DG2 G10): with this patch applied, fan2_input
> no longer appears in /sys/class/hwmon/hwmonX/ and `sensors xe-pci-0300`
> shows fan1 only.
> 
> Fixes: 28f79ac609de ("drm/xe/hwmon: expose fan speed")
> Signed-off-by: Zhan Wei <zhanwei919@gmail.com>

Sashiko has reviewed this patch and found no issues. It looks great!

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Sashiko AI review · https://sashiko.dev/#/patchset/20260527115311.13398-1-zhanwei919@gmail.com?part=1