linux-kernel - [PATCH] ACPI: CPPC: Fix bit_offset shift in MASK

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Message-Id: <20240409052310.3162495-1-jarredwhite@linux.microsoft.com>
Date: Mon,  8 Apr 2024 22:23:09 -0700
From: Jarred White <jarredwhite@...ux.microsoft.com>
To: "Rafael J. Wysocki" <rafael@...nel.org>,
	Len Brown <lenb@...nel.org>,
	Jarred White <jarredwhite@...ux.microsoft.com>,
	Easwar Hariharan <eahariha@...ux.microsoft.com>,
	linux-acpi@...r.kernel.org (open list:ACPI),
	linux-kernel@...r.kernel.org (open list)
Cc: Vanshidhar Konda <vanshikonda@...amperecomputing.com>,
	stable@...r.kernel.org
Subject: [PATCH] ACPI: CPPC: Fix bit_offset shift in MASK_VAL macro

Commit 2f4a4d63a193 ("ACPI: CPPC: Use access_width over bit_width for
system memory accesses") neglected to properly wrap the bit_offset shift
when it comes to applying the mask. This may cause incorrect values to be
read and may cause the cpufreq module not be loaded.

[   11.059751] cpu_capacity: CPU0 missing/invalid highest performance.
[   11.066005] cpu_capacity: partial information: fallback to 1024 for all CPUs

Also, corrected the bitmask generation in GENMASK (extra bit being added).

Fixes: 2f4a4d63a193 ("ACPI: CPPC: Use access_width over bit_width for system memory accesses")
Signed-off-by: Jarred White <jarredwhite@...ux.microsoft.com>
CC: Vanshidhar Konda <vanshikonda@...amperecomputing.com> 
CC: stable@...r.kernel.org #5.15+
---
 drivers/acpi/cppc_acpi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 4bfbe55553f4..00a30ca35e78 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -170,8 +170,8 @@ show_cppc_data(cppc_get_perf_ctrs, cppc_perf_fb_ctrs, wraparound_time);
 #define GET_BIT_WIDTH(reg) ((reg)->access_width ? (8 << ((reg)->access_width - 1)) : (reg)->bit_width)
 
 /* Shift and apply the mask for CPC reads/writes */
-#define MASK_VAL(reg, val) ((val) >> ((reg)->bit_offset & 			\
-					GENMASK(((reg)->bit_width), 0)))
+#define MASK_VAL(reg, val) (((val) >> (reg)->bit_offset) & 			\
+					GENMASK(((reg)->bit_width) - 1, 0))
 
 static ssize_t show_feedback_ctrs(struct kobject *kobj,
 		struct kobj_attribute *attr, char *buf)
-- 
2.33.8