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Commit be8b88d7 authored by Prakash, Prashanth's avatar Prakash, Prashanth Committed by Rafael J. Wysocki
Browse files

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: default avatarPrashanth Prakash <pprakash@codeaurora.org>
Reviewed-by: default avatarAlexey Klimov <alexey.klimov@arm.com>
Signed-off-by: default avatarRafael J. Wysocki <rafael.j.wysocki@intel.com>
parent 80b8286a

drivers/acpi/cppc_acpi.c

+44 −2
Original line number Diff line number Diff line
@@ -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);

drivers/cpufreq/cppc_cpufreq.c

+1 −0
Original line number Diff line number Diff line
@@ -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)

include/acpi/cppc_acpi.h

+1 −0
Original line number Diff line number Diff line
@@ -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*/