[PATCH v7 1/3] ACPI: CPPC: Add ospm_nominal_perf support

[Sumit Gupta <sumitg@nvidia.com>]

Expose the OSPM Nominal Performance register (ACPI 6.6, Section
8.4.6.1.2.6), which conveys the nominal performance level at which the
platform may run. Unlike the read-only Nominal Performance register, it
is writable, so OSPM can ask for a nominal level below the
platform-reported one, which then becomes the boundary between boosted
and throttled operation for the platform's power and thermal decisions.

Add cppc_set_ospm_nominal_perf() to write the register. Per the spec,
the value must lie in [Lowest Performance, Nominal Performance], which
the caller is responsible for validating.

Add cppc_ospm_nominal_perf_supported() to report whether the platform
implements the register as writable, since a write-only register cannot
be probed by reading it. Factor the writable-register check out of
cppc_set_reg_val() into cpc_reg_writable() and use it for both, so
support is never reported for a register that a write would reject.

Signed-off-by: Sumit Gupta <sumitg@nvidia.com>
---
 drivers/acpi/cppc_acpi.c | 48 ++++++++++++++++++++++++++++++++++++++--
 include/acpi/cppc_acpi.h | 10 +++++++++
 2 files changed, 56 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 9e882b3911e6..b6bf46cb06cb 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -1388,6 +1388,13 @@ static int cppc_set_reg_val_in_pcc(int cpu, struct cpc_register_resource *reg, u
 	return ret;
 }
 
+/* If a register is writeable, it must be a buffer and not null */
+static bool cpc_reg_writable(const struct cpc_register_resource *reg)
+{
+	return reg->type == ACPI_TYPE_BUFFER &&
+	       !IS_NULL_REG(&reg->cpc_entry.reg);
+}
+
 static int cppc_set_reg_val(int cpu, enum cppc_regs reg_idx, u64 val)
 {
 	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
@@ -1400,8 +1407,7 @@ static int cppc_set_reg_val(int cpu, enum cppc_regs reg_idx, u64 val)
 
 	reg = &cpc_desc->cpc_regs[reg_idx];
 
-	/* if a register is writeable, it must be a buffer and not null */
-	if ((reg->type != ACPI_TYPE_BUFFER) || IS_NULL_REG(&reg->cpc_entry.reg)) {
+	if (!cpc_reg_writable(reg)) {
 		pr_debug("CPC register is not supported\n");
 		return -EOPNOTSUPP;
 	}
@@ -1832,6 +1838,44 @@ int cppc_set_epp(int cpu, u64 epp_val)
 }
 EXPORT_SYMBOL_GPL(cppc_set_epp);
 
+/**
+ * cppc_set_ospm_nominal_perf() - Write OSPM Nominal Performance register.
+ * @cpu: CPU on which to write register.
+ * @ospm_nominal_perf: Value to write to the OSPM Nominal Performance register.
+ *
+ * OSPM Nominal Performance conveys the desired nominal performance level
+ * at which the platform may run. Per ACPI 6.6, s8.4.6.1.2.6, the value
+ * must lie within [Lowest Performance, Nominal Performance] and may be
+ * set independently of Minimum, Maximum and Desired performance. The
+ * caller is responsible for validating the range.
+ *
+ * Return: 0 on success or negative error code.
+ */
+int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
+{
+	return cppc_set_reg_val(cpu, OSPM_NOMINAL_PERF, ospm_nominal_perf);
+}
+EXPORT_SYMBOL_GPL(cppc_set_ospm_nominal_perf);
+
+/**
+ * cppc_ospm_nominal_perf_supported() - Check OSPM Nominal Performance support.
+ * @cpu: CPU to query.
+ *
+ * The OSPM Nominal Performance register is write-only, so its value
+ * cannot be read back. This only reports whether the platform implements
+ * it as a writable register.
+ *
+ * Return: true if the register is supported, false otherwise.
+ */
+bool cppc_ospm_nominal_perf_supported(int cpu)
+{
+	struct cpc_desc *cpc_desc = per_cpu(cpc_desc_ptr, cpu);
+
+	return cpc_desc &&
+	       cpc_reg_writable(&cpc_desc->cpc_regs[OSPM_NOMINAL_PERF]);
+}
+EXPORT_SYMBOL_GPL(cppc_ospm_nominal_perf_supported);
+
 /**
  * cppc_get_auto_act_window() - Read autonomous activity window register.
  * @cpu: CPU from which to read register.
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index 3394e1b208be..a078ad5964c2 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -185,6 +185,8 @@ extern int cpc_write_ffh(int cpunum, struct cpc_reg *reg, u64 val);
 extern int cppc_get_epp_perf(int cpunum, u64 *epp_perf);
 extern int cppc_set_epp_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls, bool enable);
 extern int cppc_set_epp(int cpu, u64 epp_val);
+extern int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf);
+extern bool cppc_ospm_nominal_perf_supported(int cpu);
 extern int cppc_get_auto_act_window(int cpu, u64 *auto_act_window);
 extern int cppc_set_auto_act_window(int cpu, u64 auto_act_window);
 extern int cppc_get_auto_sel(int cpu, u64 *enable);
@@ -277,6 +279,14 @@ static inline int cppc_set_epp(int cpu, u64 epp_val)
 {
 	return -EOPNOTSUPP;
 }
+static inline int cppc_set_ospm_nominal_perf(int cpu, u64 ospm_nominal_perf)
+{
+	return -EOPNOTSUPP;
+}
+static inline bool cppc_ospm_nominal_perf_supported(int cpu)
+{
+	return false;
+}
 static inline int cppc_get_auto_act_window(int cpu, u64 *auto_act_window)
 {
 	return -EOPNOTSUPP;
-- 
2.34.1