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drm/xe/hwmon: document DG2 fan speed reporting quirk

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On DG2 the driver always shows two fan channels, because the
FSC_READ_NUM_FANS command does not work on some cards. OEMs decide how
the fans map to tach channels, so two fans can share one tach line.
When that happens, the second channel reads 0 RPM even though the fan
is spinning.

Note this on the fan2_input ABI entry so the steady 0 RPM is not
mistaken for a driver bug.

Fixes: 28f79ac609 ("drm/xe/hwmon: expose fan speed")
Signed-off-by: Zhan Wei <zhanwei919@gmail.com>
Reviewed-by: Raag Jadav <raag.jadav@intel.com>
Link: https://patch.msgid.link/20260602161707.18922-1-zhanwei919@gmail.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
This commit is contained in:
Zhan Wei
2026-06-03 00:17:07 +08:00
committed by Rodrigo Vivi
parent 173202a5a3
commit ea8439751d
1 changed files with 7 additions and 0 deletions
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7
Documentation/ABI/testing/sysfs-driver-intel-xe-hwmon
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@@ -251,6 +251,13 @@ Description: RO. Fan 2 speed in RPM.
Only supported for particular Intel Xe graphics platforms.
On DG2 the driver always shows two fan channels, because the
FSC_READ_NUM_FANS command does not work on some cards. OEMs
decide how the fans map to tach channels, so two fans can share
one tach line. When that happens, the second channel
reads 0 RPM even though the fan is spinning. This is normal, not
a bug.
What: /sys/bus/pci/drivers/xe/.../hwmon/hwmon<i>/fan3_input
Date: March 2025
KernelVersion: 6.16