ACPI: CPPC: Skip desired_perf read in cppc_get_perf()

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ACPI 6.5 defines _CPC revision 3 and lists Read/Write as the Optional
Attribute of Desired Performance. ACPI 6.6 advances _CPC to revision 4 and
lists only Write. cppc_get_perf() nevertheless reads the register when
initializing performance controls, even though cppc-cpufreq overwrites the
value before using it.

Use the _CPC revision check from cppc_get_desired_perf() and leave
desired_perf zero instead of reading it for _CPC revision 4 or later. Also
exclude the register from PCC read-command detection so it cannot trigger
an otherwise unnecessary read command.

Fixes: 658fa7b1c4 ("ACPI: CPPC: Add cppc_get_perf() API to read performance controls")
Cc: stable@vger.kernel.org
Suggested-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>
Reviewed-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Link: https://patch.msgid.link/20260803203531.1268651-3-christian.loehle@arm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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Christian Loehle 2026-08-03 21:35:30 +01:00 • committed by Rafael J. Wysocki

parent df5a1d4a8c

commit d3576424e8

1 changed files with 5 additions and 2 deletions

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drivers/acpi/cppc_acpi.c

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