Re: [RFC v2 2/6] PM / Domains: prepare for devices that might register a power state

From: Marc Titinger
Date: Tue Oct 13 2015 - 06:29:59 EST

On 09/10/2015 20:22, Lina Iyer wrote:
On Fri, Oct 09 2015 at 03:39 -0600, Marc Titinger wrote:
On 08/10/2015 18:11, Lina Iyer wrote:
Hi Marc,

Thanks for rebasing on top of my latest series.

On Tue, Oct 06 2015 at 08:27 -0600, Marc Titinger wrote:
Devices may register an intermediate retention state into the domain
upon

I may agree with the usability of dynamic adding a state to the domain,
but I dont see why a device attaching to a domain should bring about a
new domain state.

Hi Lina,

thanks a lot for taking the time to look into this. The initial
discussion behind it was about to see how a device like a PMU, FPU,
cache, or a Healthcheck IP in the same power domain than CPUs, with
special retention states can be handled in a way 'unified' with CPUs.
Also I admit it is partly an attempt from us to create something
useful out of the "collision" of Axel's multiple states and your
CPUs-as-generic-power-domain-devices, hence the RFC!

Looking at Juno for instance, she currently has a platform-initiated
mode implemented in the arm-trusted-firmware through psci as a
cpuidle-driver. the menu governor will select a possibly deep c-state,
but the last-man CPU and actual power state is known to ATF. Similarly
my idea was to have a genpd-initiated mode so to say, where the actual
power state results from the cpu-domain's governor choice based on
possible retention states, and their latency.

Okay, I must admit that my ideas are quite partial to OS-initiated PSCI
(v1.0 onwards). So you have C-States that allow domains to enter idle as
well. Fair.

A Health-check IP or Cache will not (to my current knowledge) have a
driver calling runtime_put, but may have a retention state "D1_RET"
with a off/on latency between CPU_SLEEP and CLUSTER_SLEEP, so that
CLUSTER_SLEEP may be ruled out by the governor, but D1_RET is ok given
the time slot available.
A couple of questions here.

You say there is no driver for HIP, is there a device for it atleast?
How is the CPU/Domain going to know if the HIP is running or not?

To me this seems like you want to set a QoS on the PM domain here.

Some platform code can be called so that the cluster goes to D1_RET in
that case, upon the last-man CPU waiting-for-interrupt. Note that in
the case of a Health-Check HIP, the state my actually be a working
state (all CPUs power down, and time slot OK for sampling stuff).

Building on my previous statement, if you have a QoS for a domain and a
domain governor, it could consider the QoS requirement and choose to do
retention. However that needs a driver or some entity that know the HIP
is requesting a D1_RET mode only.

lets' consider a device like an L2-cache with a RAM retention state, (for instance looking at http://infocenter.arm.com/help/topic/com.arm.doc.ddi0500f/DDI0500F_cortex_a53_r0p4_trm.pdf page 41). the platform code and suspend sequence that will allow for setup of this L2 RAM Retention state will be partly common to handling deep c-states like 'CLUSTER_SLEEP'. Typically for a53, the manual describes a parent power domain PDCORTEXA53, child CPU domains PDCPUn and a child domain PDL2 that allows for L2 RAM retention. We can have all CPUs 'off' and PDL2 in retention.

In terms of 'multiple states', each CPU as a genpd device can independently set a constraint for the domain 'simple governor', ok it's not done through pm_qos_add_request, but through runtime_put, but since the c-states are soaked into the power domain as possible power-domain states, the domain will chose for the deepest possible c-state based on :

- cpus runtime_put (for c-states deeper than state0 "WFI")
- qos_requests from regular devices in the domain, or subdomains
- .. what about L2 or devices with their own power domain, that will not hook to pm_runtime ?

Beyond L2 controllers, you could have hard IPs for debug, monitoring, that will have a child power domain like above, but not necessarily hook to pm_runtime. Since the platform code for handling the CPU constraints on the domain QoS is the one for handling c-states, and the same for the L2-retention state, why not expose those constraints as all-c-states ?

I reckon that alternatively, it could be interesting to model L2-cc as a regular peripheral on its own, and hook to pm_runtime instead, but then eventually will call the same monitor code code that handles the cpu-suspend. But it's maybe less architecture dependent and more in the initial spirit of "statement-of-work" motivating this series ?

M.


A domain should define its power states, independent of the devices that
may attach. The way I see it, devices have their own idle states and
domains have their own. I do see a relationship between possible domain
states depending on the states of the individual devices in the domain.
For ex, a CPU domain can only be in a retention state (low voltage,
memory retained), if its CPU devices are in retention state, i.e, the
domain cannot be powered off; alternately, the domain may be in
retention or power down if the CPU devices are in power down state.

Could you elaborate on why this is a need?

Well, it may not be a need TBH, it is an attempt to have cluster-level
devices act like hotplugged CPUs but with heterogeneous c-states and
latencies. I hope it makes some sense :)

Hmm.. Let me think about it.

What would be a difference between a cluster-level device and a CPU in
the same domain?

-- Lina

Thanks,
Marc.



Thanks,
Lina

attaching. Currently generic domain would register an array of states
upon
init. This patch prepares for later insertion (sort per depth, remove).

Signed-off-by: Marc Titinger <mtitinger+renesas@xxxxxxxxxxxx>
---
drivers/base/power/domain.c | 189
+++++++++++++++++++-------------------------
include/linux/pm_domain.h | 18 ++++-
2 files changed, 97 insertions(+), 110 deletions(-)

diff --git a/drivers/base/power/domain.c b/drivers/base/power/domain.c
index 3e27a2b..e5f4c00b 100644
--- a/drivers/base/power/domain.c
+++ b/drivers/base/power/domain.c
@@ -19,6 +19,7 @@
#include <linux/sched.h>
#include <linux/suspend.h>
#include <linux/export.h>
+#include <linux/sort.h>

#define GENPD_RETRY_MAX_MS 250 /* Approximate */

@@ -50,12 +51,6 @@
__retval; \
})

-#define GENPD_MAX_NAME_SIZE 20
-
-static int pm_genpd_alloc_states_names(struct generic_pm_domain
*genpd,
- const struct genpd_power_state *st,
- unsigned int st_count);
-
static LIST_HEAD(gpd_list);
static DEFINE_MUTEX(gpd_list_lock);

@@ -1364,46 +1359,6 @@ static void genpd_free_dev_data(struct device
*dev,
dev_pm_put_subsys_data(dev);
}

-static int genpd_alloc_states_data(struct generic_pm_domain *genpd,
- const struct genpd_power_state *st,
- unsigned int st_count)
-{
- int ret = 0;
- unsigned int i;
-
- if (IS_ERR_OR_NULL(genpd)) {
- ret = -EINVAL;
- goto err;
- }
-
- if (!st || (st_count < 1)) {
- ret = -EINVAL;
- goto err;
- }
-
- /* Allocate the local memory to keep the states for this genpd */
- genpd->states = kcalloc(st_count, sizeof(*st), GFP_KERNEL);
- if (!genpd->states) {
- ret = -ENOMEM;
- goto err;
- }
-
- for (i = 0; i < st_count; i++) {
- genpd->states[i].power_on_latency_ns =
- st[i].power_on_latency_ns;
- genpd->states[i].power_off_latency_ns =
- st[i].power_off_latency_ns;
- }
-
- genpd->state_count = st_count;
-
- /* to save memory, Name allocation will happen if debug is
enabled */
- pm_genpd_alloc_states_names(genpd, st, st_count);
-
-err:
- return ret;
-}
-
/**
* __pm_genpd_add_device - Add a device to an I/O PM domain.
* @genpd: PM domain to add the device to.
@@ -1833,6 +1788,75 @@ static void genpd_lock_init(struct
generic_pm_domain *genpd)
}
}

+
+/*
+* state depth comparison function.
+*/
+static int state_cmp(const void *a, const void *b)
+{
+ struct genpd_power_state *state_a = (struct genpd_power_state
*)(a);
+ struct genpd_power_state *state_b = (struct genpd_power_state
*)(b);
+
+ s64 depth_a =
+ state_a->power_on_latency_ns + state_a->power_off_latency_ns;
+ s64 depth_b =
+ state_b->power_on_latency_ns + state_b->power_off_latency_ns;
+
+ return (depth_a > depth_b) ? 0 : -1;
+}
+
+/*
+* TODO: antagonist routine.
+*/
+int pm_genpd_insert_state(struct generic_pm_domain *genpd,
+ const struct genpd_power_state *state)
+{
+ int ret = 0;
+ int state_count = genpd->state_count;
+
+ if (IS_ERR_OR_NULL(genpd) || (!state))
+ ret = -EINVAL;
+
+ if (state_count >= GENPD_POWER_STATES_MAX)
+ ret = -ENOMEM;
+
+#ifdef CONFIG_PM_ADVANCED_DEBUG
+ /* to save memory, Name allocation will happen if debug is
enabled */
+ genpd->states[state_count].name = kstrndup(state->name,
+ GENPD_MAX_NAME_SIZE,
+ GFP_KERNEL);
+ if (!genpd->states[state_count].name) {
+ pr_err("%s Failed to allocate state '%s' name.\n",
+ genpd->name, state->name);
+ ret = -ENOMEM;
+ }
+#endif
+ genpd_lock(genpd);
+
+ if (!ret) {
+ genpd->states[state_count].power_on_latency_ns =
+ state->power_on_latency_ns;
+ genpd->states[state_count].power_off_latency_ns =
+ state->power_off_latency_ns;
+ genpd->state_count++;
+ }
+
+ /* sort from shallowest to deepest */
+ sort(genpd->states, genpd->state_count,
+ sizeof(genpd->states[0]), state_cmp, NULL /*generic swap */);
+
+ /* Sanity check for current state index */
+ if (genpd->state_idx >= genpd->state_count) {
+ pr_warn("pm domain %s Invalid initial state.\n", genpd->name);
+ genpd->state_idx = genpd->state_count - 1;
+ }
+
+ genpd_unlock(genpd);
+
+ return ret;
+}
+
+
/**
* pm_genpd_init - Initialize a generic I/O PM domain object.
* @genpd: PM domain object to initialize.
@@ -1846,36 +1870,24 @@ void pm_genpd_init(struct generic_pm_domain
*genpd,
const struct genpd_power_state *states,
unsigned int state_count, bool is_off)
{
- static const struct genpd_power_state genpd_default_state[] = {
- {
- .name = "OFF",
- .power_off_latency_ns = 0,
- .power_on_latency_ns = 0,
- },
- };
- int ret;
+ int i;

if (IS_ERR_OR_NULL(genpd))
return;

- /* If no states defined, use the default OFF state */
- if (!states || (state_count < 1))
- ret = genpd_alloc_states_data(genpd, genpd_default_state,
- ARRAY_SIZE(genpd_default_state));
- else
- ret = genpd_alloc_states_data(genpd, states, state_count);
-
- if (ret) {
- pr_err("Fail to allocate states for %s\n", genpd->name);
- return;
- }
+ /* simply use an array, we wish to add/remove new retention states
+ from later device init/exit. */
+ memset(genpd->states, 0, GENPD_POWER_STATES_MAX
+ * sizeof(struct genpd_power_state));

- /* Sanity check for initial state */
- if (genpd->state_idx >= genpd->state_count) {
- pr_warn("pm domain %s Invalid initial state.\n",
- genpd->name);
- genpd->state_idx = genpd->state_count - 1;
- }
+ if (!states || !state_count) {
+ /* require a provider for a default state */
+ genpd->state_count = 0;
+ genpd->state_idx = 0;
+ } else
+ for (i = 0; i < state_count; i++)
+ if (pm_genpd_insert_state(genpd, &states[i]))
+ return;

INIT_LIST_HEAD(&genpd->master_links);
INIT_LIST_HEAD(&genpd->slave_links);
@@ -2233,33 +2245,6 @@ EXPORT_SYMBOL_GPL(genpd_dev_pm_attach);
#include <linux/kobject.h>
static struct dentry *pm_genpd_debugfs_dir;

-static int pm_genpd_alloc_states_names(struct generic_pm_domain
*genpd,
- const struct genpd_power_state *st,
- unsigned int st_count)
-{
- unsigned int i;
-
- if (IS_ERR_OR_NULL(genpd))
- return -EINVAL;
-
- if (genpd->state_count != st_count) {
- pr_err("Invalid allocated state count\n");
- return -EINVAL;
- }
-
- for (i = 0; i < st_count; i++) {
- genpd->states[i].name = kstrndup(st[i].name,
- GENPD_MAX_NAME_SIZE, GFP_KERNEL);
- if (!genpd->states[i].name) {
- pr_err("%s Failed to allocate state %d name.\n",
- genpd->name, i);
- return -ENOMEM;
- }
- }
-
- return 0;
-}
-
/*
* TODO: This function is a slightly modified version of
rtpm_status_show
* from sysfs.c, so generalize it.
@@ -2398,12 +2383,4 @@ static void __exit pm_genpd_debug_exit(void)
{
debugfs_remove_recursive(pm_genpd_debugfs_dir);
}
-__exitcall(pm_genpd_debug_exit);
-#else
-static inline int pm_genpd_alloc_states_names(struct
generic_pm_domain *genpd,
- const struct genpd_power_state *st,
- unsigned int st_count)
-{
- return 0;
-}
#endif /* CONFIG_PM_ADVANCED_DEBUG */
diff --git a/include/linux/pm_domain.h b/include/linux/pm_domain.h
index 9d37292..8a4eab0 100644
--- a/include/linux/pm_domain.h
+++ b/include/linux/pm_domain.h
@@ -45,6 +45,13 @@ struct gpd_cpuidle_data {
struct cpuidle_state *idle_state;
};

+
+/* Arbitrary max number of devices registering a special
+ * retention state with the PD, to keep things simple.
+ */
+#define GENPD_POWER_STATES_MAX 12
+#define GENPD_MAX_NAME_SIZE 40
+
struct genpd_power_state {
char *name;
s64 power_off_latency_ns;
@@ -80,7 +87,8 @@ struct generic_pm_domain {
struct device *dev);
unsigned int flags; /* Bit field of configs for genpd */

- struct genpd_power_state *states;
+ struct genpd_power_state states[GENPD_POWER_STATES_MAX];
+
unsigned int state_count; /* number of states */
unsigned int state_idx; /* state that genpd will go to when off */

@@ -159,10 +167,12 @@ extern int pm_genpd_attach_cpuidle(struct
generic_pm_domain *genpd, int state);
extern int pm_genpd_name_attach_cpuidle(const char *name, int state);
extern int pm_genpd_detach_cpuidle(struct generic_pm_domain *genpd);
extern int pm_genpd_name_detach_cpuidle(const char *name);
+extern int pm_genpd_insert_state(struct generic_pm_domain *genpd,
+ const struct genpd_power_state *state);
extern void pm_genpd_init(struct generic_pm_domain *genpd,
- struct dev_power_governor *gov,
- const struct genpd_power_state *states,
- unsigned int state_count, bool is_off);
+ struct dev_power_governor *gov,
+ const struct genpd_power_state *states,
+ unsigned int state_count, bool is_off);

extern int pm_genpd_poweron(struct generic_pm_domain *genpd);
extern int pm_genpd_name_poweron(const char *domain_name);
--
1.9.1



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