ACPI / CPPC: set a non-zero value for transition_latency

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

Signed-off-by: Prashanth Prakash <pprakash@codeaurora.org>
Reviewed-by: Alexey Klimov <alexey.klimov@arm.com>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

1 files changed, 44 insertions, 2 deletions

diff --git a/drivers/acpi/cppc_acpi.c b/drivers/acpi/cppc_acpi.c
index 5623fca54ca1..6c54a8f16706 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))
@@ -473,7 +473,6 @@ 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.
@@ -483,6 +482,7 @@ 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) {
@@ -1048,3 +1048,45 @@ 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);