[PATCH V2 4/5] ACPI/CPPC: set a non-zero value for transition_latency

Prashanth Prakash
2016-07-26T19:46:03Z

Compute the expected transition latency for frequency transitions
using the values from the PCCT tables when the desired perf
register is in PCC.

Cc: "Rafael J. Wysocki" <rjw@rjwysocki.net>
Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
---
drivers/acpi/cppc_acpi.c | 46 ++++++++++++++++++++++++++++++++++++++++--
drivers/cpufreq/cppc_cpufreq.c | 1 +
include/acpi/cppc_acpi.h | 1 +
3 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 4a887d4..93abaec 100644
--- a/drivers/acpi/cppc_acpi.c
+++ b/drivers/acpi/cppc_acpi.c
@@ -85,7 +85,7 @@ static void __iomem *pcc_comm_addr;
static int pcc_subspace_idx = -1;
static bool pcc_channel_acquired;
static ktime_t deadline;
-static unsigned int pcc_mpar, pcc_mrtt;
+static unsigned int pcc_mpar, pcc_mrtt, pcc_nominal;

/* pcc mapped address + header size + offset within PCC subspace */
#define GET_PCC_VADDR(offs) (pcc_comm_addr + 0x8 + (offs))
@@ -462,7 +462,6 @@ static int register_pcc_channel(int pcc_subspace_idx)
return -ENODEV;
}

-
/*
* cppc_ss->latency is just a Nominal value. In reality
* the remote processor could be much slower to reply.
@@ -472,6 +471,7 @@ static int register_pcc_channel(int pcc_subspace_idx)
deadline = ns_to_ktime(usecs_lat * NSEC_PER_USEC);
pcc_mrtt = cppc_ss->min_turnaround_time;
pcc_mpar = cppc_ss->max_access_rate;
+ pcc_nominal = cppc_ss->latency;

pcc_comm_addr = acpi_os_ioremap(cppc_ss->base_address, cppc_ss->length);
if (!pcc_comm_addr) {
@@ -1036,3 +1036,45 @@ int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls)
return ret;
}
EXPORT_SYMBOL_GPL(cppc_set_perf);
+
+/**
+ * cppc_get_transition_latency - returns frequency transition latency in ns
+ *
+ * ACPI CPPC does not explicitly specifiy how a platform can specify the
+ * transition latency for perfromance change requests. The closest we have
+ * is the timing information from the PCCT tables which provides the info
+ * on the number and frequency of PCC commands the platform can handle.
+ */
+unsigned int cppc_get_transition_latency(int cpu_num)
+{
+ /*
+ * Expected transition latency is based on the PCCT timing values
+ * Below are definition from ACPI spec:
+ * pcc_nominal- Expected latency to process a command, in microseconds
+ * pcc_mpar - The maximum number of periodic requests that the subspace
+ * channel can support, reported in commands per minute. 0
+ * indicates no limitation.
+ * pcc_mrtt - The minimum amount of time that OSPM must wait after the
+ * completion of a command before issuing the next command,
+ * in microseconds.
+ */
+ unsigned int latency_ns = 0;
+ struct cpc_desc *cpc_desc;
+ struct cpc_register_resource *desired_reg;
+
+ cpc_desc = per_cpu(cpc_desc_ptr, cpu_num);
+ if (!cpc_desc)
+ return CPUFREQ_ETERNAL;
+
+ desired_reg = &cpc_desc->cpc_regs[DESIRED_PERF];
+ if (!CPC_IN_PCC(desired_reg))
+ return CPUFREQ_ETERNAL;
+
+ if (pcc_mpar)
+ latency_ns = 60 * (1000 * 1000 * 1000 / pcc_mpar);
+
+ latency_ns = max(latency_ns, (pcc_nominal + pcc_mrtt) * 1000);
+
+ return latency_ns;
+}
+EXPORT_SYMBOL_GPL(cppc_get_transition_latency);
diff --git a/drivers/cpufreq/cppc_cpufreq.c b/drivers/cpufreq/cppc_cpufreq.c
index 8882b8e..e6a3359 100644
--- a/drivers/cpufreq/cppc_cpufreq.c
+++ b/drivers/cpufreq/cppc_cpufreq.c
@@ -98,6 +98,7 @@ static int cppc_cpufreq_cpu_init(struct cpufreq_policy *policy)
policy->max = cpu->perf_caps.highest_perf;
policy->cpuinfo.min_freq = policy->min;
policy->cpuinfo.max_freq = policy->max;
+ policy->cpuinfo.transition_latency = cppc_get_transition_latency(cpu_num);
policy->shared_type = cpu->shared_type;

if (policy->shared_type == CPUFREQ_SHARED_TYPE_ANY)
diff --git a/include/acpi/cppc_acpi.h b/include/acpi/cppc_acpi.h
index 36ff5c6..7b7e2e1 100644
--- a/include/acpi/cppc_acpi.h
+++ b/include/acpi/cppc_acpi.h
@@ -129,5 +129,6 @@ extern int cppc_get_perf_ctrs(int cpu, struct cppc_perf_fb_ctrs *perf_fb_ctrs);
extern int cppc_set_perf(int cpu, struct cppc_perf_ctrls *perf_ctrls);
extern int cppc_get_perf_caps(int cpu, struct cppc_perf_caps *caps);
extern int acpi_get_psd_map(struct cpudata **);
+extern unsigned int cppc_get_transition_latency(int cpu);

#endif /* _CPPC_ACPI_H*/
--
Qualcomm Datacenter Technologies on behalf of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.