ACPI: CPPC: Avoid unnecessary reads for full-width writes

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SystemMemory GAS entries may describe a field within a wider access
unit, so cpc_write() reads the access unit before updating the field to
preserve the surrounding bits. It also does this when the field covers
the complete access unit.

When the bit offset is zero and the register bit width equals the
resolved access width, the previous value cannot affect the result. Skip
the MMIO read and mask operation in that case. Retain rmw_lock because
another entry in the same _CPC package may share the access unit.

Signed-off-by: Christian Loehle <christian.loehle@arm.com>
Reviewed-by: Zhongqiu Han <zhongqiu.han@oss.qualcomm.com>
Link: https://patch.msgid.link/20260803210527.1285229-2-christian.loehle@arm.com
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

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Christian Loehle 2026-08-03 22:05:25 +01:00 • committed by Rafael J. Wysocki

parent 334dd0ed87

commit 9d9157ee90

1 changed files with 26 additions and 17 deletions

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drivers/acpi/cppc_acpi.c

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