* [PATCH] ACPI: CPPC: Scale EPP values to the register width
@ 2026-11-12 13:13 Christian Loehle
2026-11-12 13:58 ` Christian Loehle
0 siblings, 1 reply; 4+ messages in thread
From: Christian Loehle @ 2026-11-12 13:13 UTC (permalink / raw)
To: Rafael J . Wysocki, viresh.kumar
Cc: linux-pm, linux-kernel, sumit.gupta, zhanjie9, superm1,
zhangpengjie2, Christian Loehle
The EPP sysfs interface uses 0-255, but ACPI permits 4-8 bit fields.
Writing 128 to a 4- or 6-bit SystemMemory field currently succeeds but
stores zero, selecting maximum performance.
Scale writes to supported narrow EPP registers and normalize reads to
0-255. Cover both EPP setters and cppc_get_perf() so saved firmware values
round-trip correctly.
Fixes: 922607a2b462 ("cpufreq: CPPC: Add support for autonomous selection")
Signed-off-by: Christian Loehle <christian.loehle@arm.com>
---
.../ABI/testing/sysfs-devices-system-cpu | 5 ++
drivers/acpi/cppc_acpi.c | 46 +++++++++++++++++--
2 files changed, 47 insertions(+), 4 deletions(-)
diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
index d219fc27a0c9..c63b5cfd993c 100644
--- a/Documentation/ABI/testing/sysfs-devices-system-cpu
+++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
@@ -322,6 +322,11 @@ Description: Energy performance preference
performance increase/decrease and the result of the hardware's
energy efficiency and performance optimization policies.
+ For supported EPP registers narrower than eight bits, values are
+ scaled and rounded to the nearest hardware preference.
+ Reads use the same 0-255 scale and may differ from the requested
+ value due to the reduced precision.
+
Writing to this file only has meaning when Autonomous Selection is
enabled.
diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 11a9f9eb6b4a..10b52163eb56 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -38,6 +38,7 @@
#include <linux/iopoll.h>
#include <linux/ktime.h>
#include <linux/list.h>
+#include <linux/math64.h>
#include <linux/mutex.h>
#include <linux/rbtree.h>
#include <linux/rwsem.h>
@@ -2841,6 +2842,25 @@ int cppc_get_highest_perf(int cpunum, u64 *highest_perf)
}
EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
+/* Keep the EPP interface on an 8-bit scale, including firmware readback. */
+static u64 cppc_scale_epp(const struct cpc_register_resource *reg,
+ u64 epp, bool to_reg)
+{
+ unsigned int width = reg->cpc_entry.reg.bit_width;
+ u32 max;
+
+ if (reg->type != ACPI_TYPE_BUFFER || width < 4 || width >= 8)
+ return epp;
+
+ max = BIT(width) - 1;
+ if (to_reg)
+ return DIV_ROUND_CLOSEST_ULL(epp * max,
+ CPPC_EPP_ENERGY_EFFICIENCY_PREF);
+
+ return DIV_ROUND_CLOSEST_ULL(epp * CPPC_EPP_ENERGY_EFFICIENCY_PREF,
+ max);
+}
+
/**
* cppc_get_epp_perf - Get the epp register value.
* @cpunum: CPU from which to get epp preference value.
@@ -2850,7 +2870,15 @@ EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
*/
int cppc_get_epp_perf(int cpunum, u64 *epp_perf)
{
- return cppc_get_reg_val(cpunum, ENERGY_PERF, epp_perf);
+ struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
+ int ret;
+
+ ret = cppc_get_reg_val(cpunum, ENERGY_PERF, epp_perf);
+ if (!ret)
+ *epp_perf = cppc_scale_epp(&cpc_desc->cpc_regs[ENERGY_PERF],
+ *epp_perf, false);
+
+ return ret;
}
EXPORT_SYMBOL_GPL(cppc_get_epp_perf);
@@ -3150,6 +3178,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
bool auto_sel_non_pcc;
bool epp_pcc;
bool epp_non_pcc;
+ u64 epp;
int ret;
if (!cpc_desc) {
@@ -3159,6 +3188,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
auto_sel_reg = &cpc_desc->cpc_regs[AUTO_SEL_ENABLE];
epp_set_reg = &cpc_desc->cpc_regs[ENERGY_PERF];
+ epp = cppc_scale_epp(epp_set_reg, perf_ctrls->energy_perf, true);
if (!enable && auto_sel_reg->type == ACPI_TYPE_INTEGER &&
auto_sel_reg->cpc_entry.int_value == 1)
return -EOPNOTSUPP;
@@ -3177,7 +3207,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
return ret;
}
if (epp_non_pcc) {
- ret = cpc_write(cpu, epp_set_reg, perf_ctrls->energy_perf);
+ ret = cpc_write(cpu, epp_set_reg, epp);
if (ret)
return ret;
}
@@ -3205,7 +3235,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
}
if (epp_pcc) {
- ret = cpc_write(cpu, epp_set_reg, perf_ctrls->energy_perf);
+ ret = cpc_write(cpu, epp_set_reg, epp);
if (ret)
goto out_unlock;
}
@@ -3235,9 +3265,17 @@ EXPORT_SYMBOL_GPL(cppc_set_epp_perf);
*/
int cppc_set_epp(int cpu, u64 epp_val)
{
+ struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
+
if (epp_val > CPPC_EPP_ENERGY_EFFICIENCY_PREF)
return -EINVAL;
+ if (!cpc_desc)
+ return -ENODEV;
+
+ epp_val = cppc_scale_epp(&cpc_desc->cpc_regs[ENERGY_PERF],
+ epp_val, true);
+
return cppc_set_reg_val(cpu, ENERGY_PERF, epp_val);
}
EXPORT_SYMBOL_GPL(cppc_set_epp);
@@ -3496,7 +3534,7 @@ int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
if (ret)
goto out_err;
}
- perf_ctrls->energy_perf = energy_perf;
+ perf_ctrls->energy_perf = cppc_scale_epp(energy_perf_reg, energy_perf, false);
if (CPC_SUPPORTED(auto_sel_reg)) {
ret = cpc_read(cpu, auto_sel_reg, &auto_sel);
--
2.34.1
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] ACPI: CPPC: Scale EPP values to the register width
2026-11-12 13:13 [PATCH] ACPI: CPPC: Scale EPP values to the register width Christian Loehle
@ 2026-11-12 13:58 ` Christian Loehle
2026-11-12 14:01 ` Rafael J. Wysocki (Intel)
0 siblings, 1 reply; 4+ messages in thread
From: Christian Loehle @ 2026-11-12 13:58 UTC (permalink / raw)
To: Rafael J . Wysocki, viresh.kumar
Cc: linux-pm, linux-kernel, zhanjie9, superm1, zhangpengjie2, Sumit Gupta
On 11/12/26 13:13, Christian Loehle wrote:
> The EPP sysfs interface uses 0-255, but ACPI permits 4-8 bit fields.
> Writing 128 to a 4- or 6-bit SystemMemory field currently succeeds but
> stores zero, selecting maximum performance.
>
> Scale writes to supported narrow EPP registers and normalize reads to
> 0-255. Cover both EPP setters and cppc_get_perf() so saved firmware values
> round-trip correctly.
>
> Fixes: 922607a2b462 ("cpufreq: CPPC: Add support for autonomous selection")
> Signed-off-by: Christian Loehle <christian.loehle@arm.com>
> ---
> .../ABI/testing/sysfs-devices-system-cpu | 5 ++
> drivers/acpi/cppc_acpi.c | 46 +++++++++++++++++--
> 2 files changed, 47 insertions(+), 4 deletions(-)
>
> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> index d219fc27a0c9..c63b5cfd993c 100644
> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> @@ -322,6 +322,11 @@ Description: Energy performance preference
> performance increase/decrease and the result of the hardware's
> energy efficiency and performance optimization policies.
>
> + For supported EPP registers narrower than eight bits, values are
> + scaled and rounded to the nearest hardware preference.
> + Reads use the same 0-255 scale and may differ from the requested
> + value due to the reduced precision.
> +
> Writing to this file only has meaning when Autonomous Selection is
> enabled.
>
> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> index 11a9f9eb6b4a..10b52163eb56 100644
> --- a/drivers/acpi/cppc_acpi.c
> +++ b/drivers/acpi/cppc_acpi.c
> @@ -38,6 +38,7 @@
> #include <linux/iopoll.h>
> #include <linux/ktime.h>
> #include <linux/list.h>
> +#include <linux/math64.h>
> #include <linux/mutex.h>
> #include <linux/rbtree.h>
> #include <linux/rwsem.h>
> @@ -2841,6 +2842,25 @@ int cppc_get_highest_perf(int cpunum, u64 *highest_perf)
> }
> EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
>
> +/* Keep the EPP interface on an 8-bit scale, including firmware readback. */
> +static u64 cppc_scale_epp(const struct cpc_register_resource *reg,
> + u64 epp, bool to_reg)
> +{
> + unsigned int width = reg->cpc_entry.reg.bit_width;
> + u32 max;
> +
> + if (reg->type != ACPI_TYPE_BUFFER || width < 4 || width >= 8)
> + return epp;
> +
> + max = BIT(width) - 1;
> + if (to_reg)
> + return DIV_ROUND_CLOSEST_ULL(epp * max,
> + CPPC_EPP_ENERGY_EFFICIENCY_PREF);
> +
> + return DIV_ROUND_CLOSEST_ULL(epp * CPPC_EPP_ENERGY_EFFICIENCY_PREF,
> + max);
> +}
> +
> /**
> * cppc_get_epp_perf - Get the epp register value.
> * @cpunum: CPU from which to get epp preference value.
> @@ -2850,7 +2870,15 @@ EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
> */
> int cppc_get_epp_perf(int cpunum, u64 *epp_perf)
> {
> - return cppc_get_reg_val(cpunum, ENERGY_PERF, epp_perf);
> + struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
> + int ret;
> +
> + ret = cppc_get_reg_val(cpunum, ENERGY_PERF, epp_perf);
> + if (!ret)
> + *epp_perf = cppc_scale_epp(&cpc_desc->cpc_regs[ENERGY_PERF],
> + *epp_perf, false);
> +
> + return ret;
> }
> EXPORT_SYMBOL_GPL(cppc_get_epp_perf);
>
> @@ -3150,6 +3178,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
> bool auto_sel_non_pcc;
> bool epp_pcc;
> bool epp_non_pcc;
> + u64 epp;
> int ret;
>
> if (!cpc_desc) {
> @@ -3159,6 +3188,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
>
> auto_sel_reg = &cpc_desc->cpc_regs[AUTO_SEL_ENABLE];
> epp_set_reg = &cpc_desc->cpc_regs[ENERGY_PERF];
> + epp = cppc_scale_epp(epp_set_reg, perf_ctrls->energy_perf, true);
> if (!enable && auto_sel_reg->type == ACPI_TYPE_INTEGER &&
> auto_sel_reg->cpc_entry.int_value == 1)
> return -EOPNOTSUPP;
> @@ -3177,7 +3207,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
> return ret;
> }
> if (epp_non_pcc) {
> - ret = cpc_write(cpu, epp_set_reg, perf_ctrls->energy_perf);
> + ret = cpc_write(cpu, epp_set_reg, epp);
> if (ret)
> return ret;
> }
> @@ -3205,7 +3235,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
> }
>
> if (epp_pcc) {
> - ret = cpc_write(cpu, epp_set_reg, perf_ctrls->energy_perf);
> + ret = cpc_write(cpu, epp_set_reg, epp);
> if (ret)
> goto out_unlock;
> }
> @@ -3235,9 +3265,17 @@ EXPORT_SYMBOL_GPL(cppc_set_epp_perf);
> */
> int cppc_set_epp(int cpu, u64 epp_val)
> {
> + struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
> +
> if (epp_val > CPPC_EPP_ENERGY_EFFICIENCY_PREF)
> return -EINVAL;
>
> + if (!cpc_desc)
> + return -ENODEV;
> +
> + epp_val = cppc_scale_epp(&cpc_desc->cpc_regs[ENERGY_PERF],
> + epp_val, true);
> +
> return cppc_set_reg_val(cpu, ENERGY_PERF, epp_val);
> }
> EXPORT_SYMBOL_GPL(cppc_set_epp);
> @@ -3496,7 +3534,7 @@ int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
> if (ret)
> goto out_err;
> }
> - perf_ctrls->energy_perf = energy_perf;
> + perf_ctrls->energy_perf = cppc_scale_epp(energy_perf_reg, energy_perf, false);
>
> if (CPC_SUPPORTED(auto_sel_reg)) {
> ret = cpc_read(cpu, auto_sel_reg, &auto_sel);
+CC Sumit's actual email, sorry about that.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] ACPI: CPPC: Scale EPP values to the register width
2026-11-12 13:58 ` Christian Loehle
@ 2026-11-12 14:01 ` Rafael J. Wysocki (Intel)
2026-11-12 14:05 ` Christian Loehle
0 siblings, 1 reply; 4+ messages in thread
From: Rafael J. Wysocki (Intel) @ 2026-11-12 14:01 UTC (permalink / raw)
To: Christian Loehle
Cc: Rafael J . Wysocki, viresh.kumar, linux-pm, linux-kernel,
zhanjie9, superm1, zhangpengjie2, Sumit Gupta
On Thu, Nov 12, 2026 at 2:58 PM Christian Loehle
<christian.loehle@arm.com> wrote:
>
> On 11/12/26 13:13, Christian Loehle wrote:
> > The EPP sysfs interface uses 0-255, but ACPI permits 4-8 bit fields.
> > Writing 128 to a 4- or 6-bit SystemMemory field currently succeeds but
> > stores zero, selecting maximum performance.
> >
> > Scale writes to supported narrow EPP registers and normalize reads to
> > 0-255. Cover both EPP setters and cppc_get_perf() so saved firmware values
> > round-trip correctly.
> >
> > Fixes: 922607a2b462 ("cpufreq: CPPC: Add support for autonomous selection")
> > Signed-off-by: Christian Loehle <christian.loehle@arm.com>
> > ---
> > .../ABI/testing/sysfs-devices-system-cpu | 5 ++
> > drivers/acpi/cppc_acpi.c | 46 +++++++++++++++++--
> > 2 files changed, 47 insertions(+), 4 deletions(-)
> >
> > diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > index d219fc27a0c9..c63b5cfd993c 100644
> > --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
> > +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
> > @@ -322,6 +322,11 @@ Description: Energy performance preference
> > performance increase/decrease and the result of the hardware's
> > energy efficiency and performance optimization policies.
> >
> > + For supported EPP registers narrower than eight bits, values are
> > + scaled and rounded to the nearest hardware preference.
> > + Reads use the same 0-255 scale and may differ from the requested
> > + value due to the reduced precision.
> > +
> > Writing to this file only has meaning when Autonomous Selection is
> > enabled.
> >
> > diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
> > index 11a9f9eb6b4a..10b52163eb56 100644
> > --- a/drivers/acpi/cppc_acpi.c
> > +++ b/drivers/acpi/cppc_acpi.c
> > @@ -38,6 +38,7 @@
> > #include <linux/iopoll.h>
> > #include <linux/ktime.h>
> > #include <linux/list.h>
> > +#include <linux/math64.h>
> > #include <linux/mutex.h>
> > #include <linux/rbtree.h>
> > #include <linux/rwsem.h>
> > @@ -2841,6 +2842,25 @@ int cppc_get_highest_perf(int cpunum, u64 *highest_perf)
> > }
> > EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
> >
> > +/* Keep the EPP interface on an 8-bit scale, including firmware readback. */
> > +static u64 cppc_scale_epp(const struct cpc_register_resource *reg,
> > + u64 epp, bool to_reg)
> > +{
> > + unsigned int width = reg->cpc_entry.reg.bit_width;
> > + u32 max;
> > +
> > + if (reg->type != ACPI_TYPE_BUFFER || width < 4 || width >= 8)
> > + return epp;
> > +
> > + max = BIT(width) - 1;
> > + if (to_reg)
> > + return DIV_ROUND_CLOSEST_ULL(epp * max,
> > + CPPC_EPP_ENERGY_EFFICIENCY_PREF);
> > +
> > + return DIV_ROUND_CLOSEST_ULL(epp * CPPC_EPP_ENERGY_EFFICIENCY_PREF,
> > + max);
> > +}
> > +
> > /**
> > * cppc_get_epp_perf - Get the epp register value.
> > * @cpunum: CPU from which to get epp preference value.
> > @@ -2850,7 +2870,15 @@ EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
> > */
> > int cppc_get_epp_perf(int cpunum, u64 *epp_perf)
> > {
> > - return cppc_get_reg_val(cpunum, ENERGY_PERF, epp_perf);
> > + struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
> > + int ret;
> > +
> > + ret = cppc_get_reg_val(cpunum, ENERGY_PERF, epp_perf);
> > + if (!ret)
> > + *epp_perf = cppc_scale_epp(&cpc_desc->cpc_regs[ENERGY_PERF],
> > + *epp_perf, false);
> > +
> > + return ret;
> > }
> > EXPORT_SYMBOL_GPL(cppc_get_epp_perf);
> >
> > @@ -3150,6 +3178,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
> > bool auto_sel_non_pcc;
> > bool epp_pcc;
> > bool epp_non_pcc;
> > + u64 epp;
> > int ret;
> >
> > if (!cpc_desc) {
> > @@ -3159,6 +3188,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
> >
> > auto_sel_reg = &cpc_desc->cpc_regs[AUTO_SEL_ENABLE];
> > epp_set_reg = &cpc_desc->cpc_regs[ENERGY_PERF];
> > + epp = cppc_scale_epp(epp_set_reg, perf_ctrls->energy_perf, true);
> > if (!enable && auto_sel_reg->type == ACPI_TYPE_INTEGER &&
> > auto_sel_reg->cpc_entry.int_value == 1)
> > return -EOPNOTSUPP;
> > @@ -3177,7 +3207,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
> > return ret;
> > }
> > if (epp_non_pcc) {
> > - ret = cpc_write(cpu, epp_set_reg, perf_ctrls->energy_perf);
> > + ret = cpc_write(cpu, epp_set_reg, epp);
> > if (ret)
> > return ret;
> > }
> > @@ -3205,7 +3235,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
> > }
> >
> > if (epp_pcc) {
> > - ret = cpc_write(cpu, epp_set_reg, perf_ctrls->energy_perf);
> > + ret = cpc_write(cpu, epp_set_reg, epp);
> > if (ret)
> > goto out_unlock;
> > }
> > @@ -3235,9 +3265,17 @@ EXPORT_SYMBOL_GPL(cppc_set_epp_perf);
> > */
> > int cppc_set_epp(int cpu, u64 epp_val)
> > {
> > + struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
> > +
> > if (epp_val > CPPC_EPP_ENERGY_EFFICIENCY_PREF)
> > return -EINVAL;
> >
> > + if (!cpc_desc)
> > + return -ENODEV;
> > +
> > + epp_val = cppc_scale_epp(&cpc_desc->cpc_regs[ENERGY_PERF],
> > + epp_val, true);
> > +
> > return cppc_set_reg_val(cpu, ENERGY_PERF, epp_val);
> > }
> > EXPORT_SYMBOL_GPL(cppc_set_epp);
> > @@ -3496,7 +3534,7 @@ int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
> > if (ret)
> > goto out_err;
> > }
> > - perf_ctrls->energy_perf = energy_perf;
> > + perf_ctrls->energy_perf = cppc_scale_epp(energy_perf_reg, energy_perf, false);
> >
> > if (CPC_SUPPORTED(auto_sel_reg)) {
> > ret = cpc_read(cpu, auto_sel_reg, &auto_sel);
>
> +CC Sumit's actual email, sorry about that.
So I'm assuming that this one is for Sumit to pick up and send again
along with a new version of
https://lore.kernel.org/linux-acpi/20261112080442.4007723-1-sumitg@nvidia.com/
Or please let me know if that is not the case.
^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: [PATCH] ACPI: CPPC: Scale EPP values to the register width
2026-11-12 14:01 ` Rafael J. Wysocki (Intel)
@ 2026-11-12 14:05 ` Christian Loehle
0 siblings, 0 replies; 4+ messages in thread
From: Christian Loehle @ 2026-11-12 14:05 UTC (permalink / raw)
To: Rafael J. Wysocki (Intel)
Cc: viresh.kumar, linux-pm, linux-kernel, zhanjie9, superm1,
zhangpengjie2, Sumit Gupta
On 11/12/26 14:01, Rafael J. Wysocki (Intel) wrote:
> On Thu, Nov 12, 2026 at 2:58 PM Christian Loehle
> <christian.loehle@arm.com> wrote:
>>
>> On 11/12/26 13:13, Christian Loehle wrote:
>>> The EPP sysfs interface uses 0-255, but ACPI permits 4-8 bit fields.
>>> Writing 128 to a 4- or 6-bit SystemMemory field currently succeeds but
>>> stores zero, selecting maximum performance.
>>>
>>> Scale writes to supported narrow EPP registers and normalize reads to
>>> 0-255. Cover both EPP setters and cppc_get_perf() so saved firmware values
>>> round-trip correctly.
>>>
>>> Fixes: 922607a2b462 ("cpufreq: CPPC: Add support for autonomous selection")
>>> Signed-off-by: Christian Loehle <christian.loehle@arm.com>
>>> ---
>>> .../ABI/testing/sysfs-devices-system-cpu | 5 ++
>>> drivers/acpi/cppc_acpi.c | 46 +++++++++++++++++--
>>> 2 files changed, 47 insertions(+), 4 deletions(-)
>>>
>>> diff --git a/Documentation/ABI/testing/sysfs-devices-system-cpu b/Documentation/ABI/testing/sysfs-devices-system-cpu
>>> index d219fc27a0c9..c63b5cfd993c 100644
>>> --- a/Documentation/ABI/testing/sysfs-devices-system-cpu
>>> +++ b/Documentation/ABI/testing/sysfs-devices-system-cpu
>>> @@ -322,6 +322,11 @@ Description: Energy performance preference
>>> performance increase/decrease and the result of the hardware's
>>> energy efficiency and performance optimization policies.
>>>
>>> + For supported EPP registers narrower than eight bits, values are
>>> + scaled and rounded to the nearest hardware preference.
>>> + Reads use the same 0-255 scale and may differ from the requested
>>> + value due to the reduced precision.
>>> +
>>> Writing to this file only has meaning when Autonomous Selection is
>>> enabled.
>>>
>>> diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
>>> index 11a9f9eb6b4a..10b52163eb56 100644
>>> --- a/drivers/acpi/cppc_acpi.c
>>> +++ b/drivers/acpi/cppc_acpi.c
>>> @@ -38,6 +38,7 @@
>>> #include <linux/iopoll.h>
>>> #include <linux/ktime.h>
>>> #include <linux/list.h>
>>> +#include <linux/math64.h>
>>> #include <linux/mutex.h>
>>> #include <linux/rbtree.h>
>>> #include <linux/rwsem.h>
>>> @@ -2841,6 +2842,25 @@ int cppc_get_highest_perf(int cpunum, u64 *highest_perf)
>>> }
>>> EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
>>>
>>> +/* Keep the EPP interface on an 8-bit scale, including firmware readback. */
>>> +static u64 cppc_scale_epp(const struct cpc_register_resource *reg,
>>> + u64 epp, bool to_reg)
>>> +{
>>> + unsigned int width = reg->cpc_entry.reg.bit_width;
>>> + u32 max;
>>> +
>>> + if (reg->type != ACPI_TYPE_BUFFER || width < 4 || width >= 8)
>>> + return epp;
>>> +
>>> + max = BIT(width) - 1;
>>> + if (to_reg)
>>> + return DIV_ROUND_CLOSEST_ULL(epp * max,
>>> + CPPC_EPP_ENERGY_EFFICIENCY_PREF);
>>> +
>>> + return DIV_ROUND_CLOSEST_ULL(epp * CPPC_EPP_ENERGY_EFFICIENCY_PREF,
>>> + max);
>>> +}
>>> +
>>> /**
>>> * cppc_get_epp_perf - Get the epp register value.
>>> * @cpunum: CPU from which to get epp preference value.
>>> @@ -2850,7 +2870,15 @@ EXPORT_SYMBOL_GPL(cppc_get_highest_perf);
>>> */
>>> int cppc_get_epp_perf(int cpunum, u64 *epp_perf)
>>> {
>>> - return cppc_get_reg_val(cpunum, ENERGY_PERF, epp_perf);
>>> + struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpunum);
>>> + int ret;
>>> +
>>> + ret = cppc_get_reg_val(cpunum, ENERGY_PERF, epp_perf);
>>> + if (!ret)
>>> + *epp_perf = cppc_scale_epp(&cpc_desc->cpc_regs[ENERGY_PERF],
>>> + *epp_perf, false);
>>> +
>>> + return ret;
>>> }
>>> EXPORT_SYMBOL_GPL(cppc_get_epp_perf);
>>>
>>> @@ -3150,6 +3178,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
>>> bool auto_sel_non_pcc;
>>> bool epp_pcc;
>>> bool epp_non_pcc;
>>> + u64 epp;
>>> int ret;
>>>
>>> if (!cpc_desc) {
>>> @@ -3159,6 +3188,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
>>>
>>> auto_sel_reg = &cpc_desc->cpc_regs[AUTO_SEL_ENABLE];
>>> epp_set_reg = &cpc_desc->cpc_regs[ENERGY_PERF];
>>> + epp = cppc_scale_epp(epp_set_reg, perf_ctrls->energy_perf, true);
>>> if (!enable && auto_sel_reg->type == ACPI_TYPE_INTEGER &&
>>> auto_sel_reg->cpc_entry.int_value == 1)
>>> return -EOPNOTSUPP;
>>> @@ -3177,7 +3207,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
>>> return ret;
>>> }
>>> if (epp_non_pcc) {
>>> - ret = cpc_write(cpu, epp_set_reg, perf_ctrls->energy_perf);
>>> + ret = cpc_write(cpu, epp_set_reg, epp);
>>> if (ret)
>>> return ret;
>>> }
>>> @@ -3205,7 +3235,7 @@ int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable)
>>> }
>>>
>>> if (epp_pcc) {
>>> - ret = cpc_write(cpu, epp_set_reg, perf_ctrls->energy_perf);
>>> + ret = cpc_write(cpu, epp_set_reg, epp);
>>> if (ret)
>>> goto out_unlock;
>>> }
>>> @@ -3235,9 +3265,17 @@ EXPORT_SYMBOL_GPL(cppc_set_epp_perf);
>>> */
>>> int cppc_set_epp(int cpu, u64 epp_val)
>>> {
>>> + struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
>>> +
>>> if (epp_val > CPPC_EPP_ENERGY_EFFICIENCY_PREF)
>>> return -EINVAL;
>>>
>>> + if (!cpc_desc)
>>> + return -ENODEV;
>>> +
>>> + epp_val = cppc_scale_epp(&cpc_desc->cpc_regs[ENERGY_PERF],
>>> + epp_val, true);
>>> +
>>> return cppc_set_reg_val(cpu, ENERGY_PERF, epp_val);
>>> }
>>> EXPORT_SYMBOL_GPL(cppc_set_epp);
>>> @@ -3496,7 +3534,7 @@ int cppc_get_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
>>> if (ret)
>>> goto out_err;
>>> }
>>> - perf_ctrls->energy_perf = energy_perf;
>>> + perf_ctrls->energy_perf = cppc_scale_epp(energy_perf_reg, energy_perf, false);
>>>
>>> if (CPC_SUPPORTED(auto_sel_reg)) {
>>> ret = cpc_read(cpu, auto_sel_reg, &auto_sel);
>>
>> +CC Sumit's actual email, sorry about that.
>
> So I'm assuming that this one is for Sumit to pick up and send again
> along with a new version of
>
> https://lore.kernel.org/linux-acpi/20261112080442.4007723-1-sumitg@nvidia.com/
>
> Or please let me know if that is not the case.
Yup, while it fixes an issue by itself technically, I don't think there
are any affected platforms.
I'm hoping that Sumit this (and the limit-write-at-init) patch as a series
for all our convenience (and hopefully to get Sashiko to review them too).
(I guess I should've mentioned that in the notes.)
And sorry about ACPI/CPPC having such high traffic lately, I'm expecting once
we've got the issues ironed out and the new features supported it'll be a
lot more boring :)
^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2026-11-12 14:06 UTC | newest]
Thread overview: 4+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2026-11-12 13:13 [PATCH] ACPI: CPPC: Scale EPP values to the register width Christian Loehle
2026-11-12 13:58 ` Christian Loehle
2026-11-12 14:01 ` Rafael J. Wysocki (Intel)
2026-11-12 14:05 ` Christian Loehle
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