Re: [PATCH v6 4/5] arm64: add support for ACPI Low Power Idle(LPI)

From: Daniel Lezcano
Date: Mon Jun 27 2016 - 12:29:29 EST

On 06/22/2016 04:17 PM, Lorenzo Pieralisi wrote:
Hi Sudeep,

On Tue, Jun 14, 2016 at 03:48:38PM +0100, Sudeep Holla wrote:
This patch adds appropriate callbacks to support ACPI Low Power Idle
(LPI) on ARM64.

Now that arm_enter_idle_state is exactly same in both generic ARM{32,64}
CPUIdle driver and ARM64 backend for ACPI processor idle driver, we can
unify it and move to cpuidle-arm.h header.

Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx>
Cc: Mark Rutland <mark.rutland@xxxxxxx>
Cc: Daniel Lezcano <daniel.lezcano@xxxxxxxxxx>
Cc: "Rafael J. Wysocki" <rjw@xxxxxxxxxxxxx>
Cc: linux-arm-kernel@xxxxxxxxxxxxxxxxxxx
Signed-off-by: Sudeep Holla <sudeep.holla@xxxxxxx>
---
arch/arm64/kernel/cpuidle.c | 17 +++++++++++++
drivers/cpuidle/cpuidle-arm.c | 23 ++----------------
drivers/firmware/psci.c | 56 +++++++++++++++++++++++++++++++++++++++++++
include/linux/cpuidle-arm.h | 30 +++++++++++++++++++++++
4 files changed, 105 insertions(+), 21 deletions(-)
create mode 100644 include/linux/cpuidle-arm.h

This patch seems fine by me, it would be good if Daniel can have
a look too.

Some minor comments below.

[...]

diff --git a/drivers/firmware/psci.c b/drivers/firmware/psci.c
index 03e04582791c..c6caa863d156 100644
--- a/drivers/firmware/psci.c
+++ b/drivers/firmware/psci.c
@@ -13,6 +13,7 @@

#define pr_fmt(fmt) "psci: " fmt

+#include <linux/acpi.h>
#include <linux/arm-smccc.h>
#include <linux/cpuidle.h>
#include <linux/errno.h>
@@ -310,11 +311,66 @@ static int psci_dt_cpu_init_idle(struct device_node *cpu_node, int cpu)
return ret;
}

+#ifdef CONFIG_ACPI
+#include <acpi/processor.h>
+
+static int __maybe_unused psci_acpi_cpu_init_idle(unsigned int cpu)
+{
+ int i, count;
+ u32 *psci_states;
+ struct acpi_processor *pr;
+ struct acpi_lpi_state *lpi;
+
+ pr = per_cpu(processors, cpu);
+ if (unlikely(!pr || !pr->flags.has_lpi))
+ return -EINVAL;
+
+ /*
+ * If the PSCI cpu_suspend function hook has not been initialized
+ * idle states must not be enabled, so bail out
+ */
+ if (!psci_ops.cpu_suspend)
+ return -EOPNOTSUPP;
+
+ count = pr->power.count - 1;
+ if (count <= 0)
+ return -ENODEV;
+
+ psci_states = kcalloc(count, sizeof(*psci_states), GFP_KERNEL);
+ if (!psci_states)
+ return -ENOMEM;
+
+ for (i = 0; i < count; i++) {
+ u32 state;
+
+ lpi = &pr->power.lpi_states[i + 1];
+ state = lpi->address & 0xFFFFFFFF;

Why mask 'address' if 'state' is u32 ?

+ if (!psci_power_state_is_valid(state)) {
+ pr_warn("Invalid PSCI power state %#x\n", state);
+ kfree(psci_states);
+ return -EINVAL;
+ }
+ psci_states[i] = state;
+ }
+ /* Idle states parsed correctly, initialize per-cpu pointer */
+ per_cpu(psci_power_state, cpu) = psci_states;
+ return 0;

The ACPI and the PSCI code are not self contained here.

It would be nice to move this function to the ACPI code.

+}
+#else
+static int __maybe_unused psci_acpi_cpu_init_idle(unsigned int cpu)
+{
+ return -EINVAL;
+}
+#endif
+
int psci_cpu_init_idle(unsigned int cpu)
{
struct device_node *cpu_node;
int ret;

+ if (!acpi_disabled)
+ return psci_acpi_cpu_init_idle(cpu);
+

acpi_disabled - acpi_disabled - acpi_disabled everywhere :/

The enable-method approach is not straightforward and now it is polluted by acpi-disabled.

So IIUC,

smp_init_cpus (contains acpi_disabled)
smp_cpu_setup
cpu_read_ops
cpu_read_enable_method (contains acpi_disabled)
acpi_get_enable_method (returns 'psci' after checking psci_is_present)

Then psci_cpu_init_idle is called... and check again acpi_disabled.

IMO, the circumlocution with the psci vs acpi vs acpi_disabled is getting unnecessary too complex, is prone to error and will lead to unmaintainable code very soon.

I suggest to sort out encapsulation and self-contained code before adding more feature in this area.


cpu_node = of_get_cpu_node(cpu, NULL);
if (!cpu_node)
return -ENODEV;
diff --git a/include/linux/cpuidle-arm.h b/include/linux/cpuidle-arm.h
new file mode 100644
index 000000000000..b99bcb3f43dd
--- /dev/null
+++ b/include/linux/cpuidle-arm.h

arm-cpuidle.h for consistency with other (ARM) include/linux files ?

@@ -0,0 +1,30 @@
+#include <linux/cpu_pm.h>
+
+#include <asm/cpuidle.h>
+
+/*
+ * arm_enter_idle_state - Programs CPU to enter the specified state
+ */
+static int arm_generic_enter_idle_state(int idx)
+{
+ int ret;
+
+ if (!idx) {
+ cpu_do_idle();
+ return idx;
+ }
+
+ ret = cpu_pm_enter();
+ if (!ret) {
+ /*
+ * Pass idle state index to cpu_suspend which in turn will
+ * call the CPU ops suspend protocol with idle index as a
+ * parameter.
+ */
+ ret = arm_cpuidle_suspend(idx);
+
+ cpu_pm_exit();
+ }
+
+ return ret ? -1 : idx;
+}

Either you do this, or we have to add it somehow somewhere in
drivers/cpuidle to avoid duplicating it.

@Daniel: do you have an opinion on this please ?

I don't like the idea to add an ARM arch specific header in include/linux. I thought this directory was supposed to contain as much as possible arch agnostic headers.

May be the name can be changed to something more generic:

eg.

int cpuidle_generic_enter(int idx);

and then add an option:

HAVE_CPUIDLE_GENERIC_ENTER

, then in the generic header:

#ifdef HAVE_CPUIDLE_GENERIC_ENTER
int cpuidle_generic_enter(int idx);
#endif

, change the function name in cpuidle-arm .c

and finally add in the ARM and ARM64 Kconfig's option HAVE_CPUIDLE_GENERIC_ENTER.


-- Daniel

--
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