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

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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>
This commit is contained in:
Prakash, Prashanth 2016-08-16 14:39:41 -06:00 committed by Rafael J. Wysocki
parent 80b8286aee
commit be8b88d7d9
3 changed files with 46 additions and 2 deletions
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46
drivers/acpi/cppc_acpi.c
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@ -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);

1
drivers/cpufreq/cppc_cpufreq.c
View File

@ -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)

1
include/acpi/cppc_acpi.h
View File

@ -131,5 +131,6 @@ 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*/