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

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Message-ID: <CAJZ5v0imiRbheOJgEf=Ua-JRhDTh1+SJ-=CjUC7vOQYffV50FA@mail.gmail.com>
Date: Mon, 22 Apr 2024 18:43:26 +0200
From: "Rafael J. Wysocki" <rafael@...nel.org>
To: Vanshidhar Konda <vanshikonda@...amperecomputing.com>, 
	Jarred White <jarredwhite@...ux.microsoft.com>
Cc: "Rafael J. Wysocki" <rafael@...nel.org>, Len Brown <lenb@...nel.org>, 
	Easwar Hariharan <eahariha@...ux.microsoft.com>, 
	"open list:ACPI" <linux-acpi@...r.kernel.org>, open list <linux-kernel@...r.kernel.org>, 
	stable@...r.kernel.org
Subject: Re: [PATCH] ACPI: CPPC: Fix bit_offset shift in MASK_VAL macro

On Wed, Apr 17, 2024 at 7:37 PM Vanshidhar Konda
<vanshikonda@...amperecomputing.com> wrote:
>
> Looks good to me.
>
> Reviewed-by: Vanshidhar Konda <vanshikonda@...amperecomputing.com>
>
> On Mon, Apr 08, 2024 at 10:23:09PM -0700, Jarred White wrote:
> >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)
> >--

Applied as 6.9-rc material, thanks!