Re: [PATCH v2 2/3] cpufreq: qcom-nvmem: Enable virtual power domain devices

[Stephan Gerhold <stephan.gerhold@kernkonzept.com>]

On Wed, Oct 25, 2023 at 12:05:49PM +0200, Ulf Hansson wrote:
> On Tue, 24 Oct 2023 at 18:25, Stephan Gerhold <stephan@gerhold.net> wrote:
> > On Tue, Oct 24, 2023 at 06:11:34PM +0200, Ulf Hansson wrote:
> > > On Tue, 24 Oct 2023 at 15:07, Stephan Gerhold
> > > <stephan.gerhold@kernkonzept.com> wrote:
> > > > On Tue, Oct 24, 2023 at 02:49:32PM +0200, Ulf Hansson wrote:
> > > > > On Tue, 24 Oct 2023 at 14:03, Stephan Gerhold
> > > > > <stephan.gerhold@kernkonzept.com> wrote:
> > > > > > On Thu, Oct 19, 2023 at 01:26:19PM +0200, Ulf Hansson wrote:
> > > > > > > On Thu, 19 Oct 2023 at 12:24, Ulf Hansson <ulf.hansson@linaro.org> wrote:
> > > > > > > > On Wed, 18 Oct 2023 at 10:06, Stephan Gerhold
> > > > > > > > <stephan.gerhold@kernkonzept.com> wrote:
> > > > > > > > >
> > > > > > > > > The genpd core caches performance state votes from devices that are
> > > > > > > > > runtime suspended as of commit 3c5a272202c2 ("PM: domains: Improve
> > > > > > > > > runtime PM performance state handling"). They get applied once the
> > > > > > > > > device becomes active again.
> > > > > > > > >
> > > > > > > > > To attach the power domains needed by qcom-cpufreq-nvmem the OPP core
> > > > > > > > > calls genpd_dev_pm_attach_by_id(). This results in "virtual" dummy
> > > > > > > > > devices that use runtime PM only to control the enable and performance
> > > > > > > > > state for the attached power domain.
> > > > > > > > >
> > > > > > > > > However, at the moment nothing ever resumes the virtual devices created
> > > > > > > > > for qcom-cpufreq-nvmem. They remain permanently runtime suspended. This
> > > > > > > > > means that performance state votes made during cpufreq scaling get
> > > > > > > > > always cached and never applied to the hardware.
> > > > > > > > >
> > > > > > > > > Fix this by enabling the devices after attaching them and use
> > > > > > > > > dev_pm_syscore_device() to ensure the power domains also stay on when
> > > > > > > > > going to suspend. Since it supplies the CPU we can never turn it off
> > > > > > > > > from Linux. There are other mechanisms to turn it off when needed,
> > > > > > > > > usually in the RPM firmware (RPMPD) or the cpuidle path (CPR genpd).
> > > > > > > >
> > > > > > > > I believe we discussed using dev_pm_syscore_device() for the previous
> > > > > > > > version. It's not intended to be used for things like the above.
> > > > > > > >
> > > > > > > > Moreover, I was under the impression that it wasn't really needed. In
> > > > > > > > fact, I would think that this actually breaks things for system
> > > > > > > > suspend/resume, as in this case the cpr driver's genpd
> > > > > > > > ->power_on|off() callbacks are no longer getting called due this,
> > > > > > > > which means that the cpr state machine isn't going to be restored
> > > > > > > > properly. Or did I get this wrong?
> > > > > > >
> > > > > > > BTW, if you really need something like the above, the proper way to do
> > > > > > > it would instead be to call device_set_awake_path() for the device.
> > > > > > >
> > > > > >
> > > > > > Unfortunately this does not work correctly. When I use
> > > > > > device_set_awake_path() it does set dev->power.wakeup_path = true.
> > > > > > However, this flag is cleared again in device_prepare() when entering
> > > > > > suspend. To me it looks a bit like wakeup_path is not supposed to be set
> > > > > > directly by drivers? Before and after your commit 8512220c5782 ("PM /
> > > > > > core: Assign the wakeup_path status flag in __device_prepare()") it
> > > > > > seems to be internally bound to device_may_wakeup().
> > > > > >
> > > > > > It works if I make device_may_wakeup() return true, with
> > > > > >
> > > > > >         device_set_wakeup_capable(dev, true);
> > > > > >         device_wakeup_enable(dev);
> > > > > >
> > > > > > but that also allows *disabling* the wakeup from sysfs which doesn't
> > > > > > really make sense for the CPU.
> > > > > >
> > > > > > Any ideas?
> > > > >
> > > > > The device_set_awake_path() should be called from a system suspend
> > > > > callback. So you need to add that callback for the cpufreq driver.
> > > > >
> > > > > Sorry, if that wasn't clear.
> > > > >
> > > >
> > > > Hmm, but at the moment I'm calling this on the virtual genpd devices.
> > > > How would it work for them? I don't have a suspend callback for them.
> > > >
> > > > I guess could loop over the virtual devices in the cpufreq driver
> > > > suspend callback, but is my driver suspend callback really guaranteed to
> > > > run before the device_prepare() that clears "wakeup_path" on the virtual
> > > > devices?
> > >
> > > Yes, that's guaranteed. dpm_prepare() (which calls device_prepare())
> > > is always being executed before dpm_suspend().
> > >
> >
> > Thanks, I think I understand. Maybe. :-)
> >
> > Just to confirm, I should call device_set_awake_path() for the virtual
> > genpd devices as part of the PM ->suspend() callback? And this will be
> > guaranteed to run after the "prepare" phase but before the
> > "suspend_noirq" phase where the genpd core will check the wakeup flag?
> 
> Correct!
> 

Thanks, this seems to works as intended! The diff I tested is below, in
case you already have some comments.

I'll put this into proper patches and will send a v3 after the merge
window.

Stephan

diff --git a/drivers/cpufreq/qcom-cpufreq-nvmem.c b/drivers/cpufreq/qcom-cpufreq-nvmem.c
index 7e9202080c98..e0c82c958018 100644
--- a/drivers/cpufreq/qcom-cpufreq-nvmem.c
+++ b/drivers/cpufreq/qcom-cpufreq-nvmem.c
@@ -23,6 +23,7 @@
 #include <linux/nvmem-consumer.h>
 #include <linux/of.h>
 #include <linux/platform_device.h>
+#include <linux/pm.h>
 #include <linux/pm_domain.h>
 #include <linux/pm_opp.h>
 #include <linux/pm_runtime.h>
@@ -426,6 +427,18 @@ static const struct qcom_cpufreq_match_data match_data_ipq8074 = {
 	.get_version = qcom_cpufreq_ipq8074_name_version,
 };
 
+static void qcom_cpufreq_suspend_virt_devs(struct qcom_cpufreq_drv *drv, unsigned cpu)
+{
+	const char * const *name = drv->data->genpd_names;
+	int i;
+
+	if (!drv->cpus[cpu].virt_devs)
+		return;
+
+	for (i = 0; *name; i++, name++)
+		device_set_awake_path(drv->cpus[cpu].virt_devs[i]);
+}
+
 static void qcom_cpufreq_put_virt_devs(struct qcom_cpufreq_drv *drv, unsigned cpu)
 {
 	const char * const *name = drv->data->genpd_names;
@@ -542,9 +555,6 @@ static int qcom_cpufreq_probe(struct platform_device *pdev)
 
 					goto free_opp;
 				}
-
-				/* Keep CPU power domain always-on */
-				dev_pm_syscore_device(virt_devs[i], true);
 			}
 			drv->cpus[cpu].virt_devs = virt_devs;
 		}
@@ -581,11 +591,25 @@ static void qcom_cpufreq_remove(struct platform_device *pdev)
 	}
 }
 
+static int qcom_cpufreq_suspend(struct device *dev)
+{
+	struct qcom_cpufreq_drv *drv = dev_get_drvdata(dev);
+	unsigned int cpu;
+
+	for_each_possible_cpu(cpu)
+		qcom_cpufreq_suspend_virt_devs(drv, cpu);
+
+	return 0;
+}
+
+static DEFINE_SIMPLE_DEV_PM_OPS(qcom_cpufreq_pm_ops, qcom_cpufreq_suspend, NULL);
+
 static struct platform_driver qcom_cpufreq_driver = {
 	.probe = qcom_cpufreq_probe,
 	.remove_new = qcom_cpufreq_remove,
 	.driver = {
 		.name = "qcom-cpufreq-nvmem",
+		.pm = pm_sleep_ptr(&qcom_cpufreq_pm_ops),
 	},
 };
 
diff --git a/drivers/pmdomain/qcom/rpmpd.c b/drivers/pmdomain/qcom/rpmpd.c
index abb62e4a2bdf..0f91e00b5909 100644
--- a/drivers/pmdomain/qcom/rpmpd.c
+++ b/drivers/pmdomain/qcom/rpmpd.c
@@ -1050,6 +1050,7 @@ static int rpmpd_probe(struct platform_device *pdev)
 		rpmpds[i]->pd.power_off = rpmpd_power_off;
 		rpmpds[i]->pd.power_on = rpmpd_power_on;
 		rpmpds[i]->pd.set_performance_state = rpmpd_set_performance;
+		rpmpds[i]->pd.flags = GENPD_FLAG_ACTIVE_WAKEUP;
 		pm_genpd_init(&rpmpds[i]->pd, NULL, true);
 
 		data->domains[i] = &rpmpds[i]->pd;

-- 
Stephan Gerhold <stephan.gerhold@kernkonzept.com>
Kernkonzept GmbH at Dresden, Germany, HRB 31129, CEO Dr.-Ing. Michael Hohmuth