On Wed, Jun 25, 2014 at 04:59:49PM +0100, Mark Rutland wrote:

On Wed, Jun 25, 2014 at 03:10:16PM +0100, Lorenzo Pieralisi wrote:

[...]

quoted

diff --git a/drivers/cpuidle/dt_idle_states.c b/drivers/cpuidle/dt_idle_states.c
new file mode 100644
index 0000000..5c16001c
--- /dev/null
+++ b/drivers/cpuidle/dt_idle_states.c

@@ -0,0 +1,283 @@
+/*
+ * DT idle states parsing code.
+ *
+ * Copyright (C) 2014 ARM Ltd.
+ * Author: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#define pr_fmt(fmt) "DT idle-states: " fmt
+
+#include <linux/cpuidle.h>
+#include <linux/cpumask.h>
+#include <linux/errno.h>
+#include <linux/kernel.h>
+#include <linux/list.h>
+#include <linux/list_sort.h>
+#include <linux/module.h>
+#include <linux/of.h>
+#include <linux/slab.h>
+
+#include "dt_idle_states.h"
+
+struct state_elem {
+	struct list_head list;
+	struct device_node *node;
+	u32 val;
+};

Ah. So the fixed-size entry parameter requirement is because this code
is in charge of allocating and freeing these structs?

Nope, I use this struct to sort the states and val is the value that
determines the order (ie power-rank) in this patch. If I used the
phandle lists for ordering nodes, this struct would disappear completely,
I have to check if that's feasible.

quoted

+
+static struct list_head head __initdata = LIST_HEAD_INIT(head);
+
+static bool __init state_cpu_valid(struct device_node *state_node,
+				   struct device_node *cpu_node)
+{
+	int i = 0;
+	struct device_node *cpu_state;
+
+	while ((cpu_state = of_parse_phandle(cpu_node,
+					     "cpu-idle-states", i++))) {
+		if (cpu_state && state_node == cpu_state) {

You can drop the cpu_state NULL check, it's implicit in the while loop.

Yep.

quoted

+			of_node_put(cpu_state);
+			return true;
+		}
+		of_node_put(cpu_state);
+	}
+	return false;
+}

Is it possible to use a bool ret variable to avoid the two of_node_put
cases? Or does that end up making this larger?

No, I think you are right.

quoted

+static bool __init state_cpus_valid(const cpumask_t *cpus,
+				    struct device_node *state_node)
+{
+	int cpu;
+	struct device_node *cpu_node;
+
+	/*
+	 * Check if state is valid on driver cpumask cpus
+	 */
+	for_each_cpu(cpu, cpus) {
+		cpu_node = of_get_cpu_node(cpu, NULL);
+
+		if (!cpu_node) {
+			pr_err("Missing device node for CPU %d\n", cpu);
+			return false;
+		}
+
+		if (!state_cpu_valid(state_node, cpu_node))
+			return false;
+	}
+
+	return true;
+}

Doesn't this leave all the cpu node refcounts incremented? (it's painful
to get device node refcounting right, I know).

I think you can use the similarly named of_cpu_device_node_get to find
the CPU node. It uses the pointer stored in cpu->dev.of_node, so it
doesn't have to walk the tree to find the CPU node. It also doesn't
increment the refcount.

Unless this is too early for that?

I think I can use of_cpu_device_node_get(...), but I should still manage
refcount properly on that, which I am not doing here, good catch.

quoted

+static void __init init_state_node(struct cpuidle_driver *drv,
+				   struct device_node *state_node,
+				   int *cnt)
+{
+	struct cpuidle_state *idle_state;
+
+	pr_debug(" * %s...\n", state_node->full_name);
+
+	idle_state = &drv->states[*cnt];
+
+	if (of_property_read_u32(state_node, "wakeup-latency-us",
+				 &idle_state->exit_latency)) {

I'm not a fan of this construction, as the obvious reading is that we
take the branch if we succeeded (which obviously isn't true as
of_property_read_* return error codes). 

Could we change it to something like:

	err = of_property_read_u32(state_node, "wakeup-latency-us",
				   &idle_state->exit_latency);
	if (err) {

You are right, I will update it.

quoted

+		u32 entry_latency, exit_latency;
+
+		if (of_property_read_u32(state_node, "entry-latency-us",
+					 &entry_latency)) {
+			pr_debug(" * %s missing entry-latency-us property\n",
+				 state_node->full_name);
+			return;
+		}

Returning without error code? Do the fields have sane default values?

Or is this safe because we didn't increment cnt?

The latter, but it isn't nice, agreed, it is just an internal interface
though. I will make it less opaque and easier to understand.

quoted

+
+		if (of_property_read_u32(state_node, "exit-latency-us",
+					 &exit_latency)) {
+			pr_debug(" * %s missing exit-latency-us property\n",
+				 state_node->full_name);
+			return;
+		}
+		/*
+		 * If wakeup-latency-us is missing, default to entry+exit
+		 * latencies as defined in idle states bindings
+		 */
+		idle_state->exit_latency = entry_latency + exit_latency;
+	}
+
+	if (of_property_read_u32(state_node, "min-residency-us",
+				 &idle_state->target_residency)) {
+		pr_debug(" * %s missing min-residency-us property\n",
+			     state_node->full_name);
+		return;
+	}
+
+	idle_state->flags = CPUIDLE_FLAG_TIME_VALID;
+	if (!of_property_read_bool(state_node, "timer-state-retained"))
+		idle_state->flags |= CPUIDLE_FLAG_TIMER_STOP;
+ 	strncpy(idle_state->name, state_node->name, CPUIDLE_NAME_LEN);
+	strncpy(idle_state->desc, state_node->name, CPUIDLE_NAME_LEN);

Does the name make sense as a desc? Is a desc necessary?

CPUIDLE_DESC_LEN seems to exist, and is double CPUIDLE_NAME_LEN.

Yes, that's a copy and paste typo that I missed. BTW this code is likely
to disappear, since the way CPUidle driver manages these strings is changing.

As to is desc really needed, I need to check all existing drivers to
provide a complete answer.

quoted

+static void __init add_idle_states(struct cpuidle_driver *drv,
+				   struct device_node *idle_states)
+{
+	struct device_node *state_node;
+
+	for_each_child_of_node(idle_states, state_node) {
+		if ((!of_device_is_compatible(state_node, "arm,idle-state"))) {

Holy brackets batman! I think we can drop the outer ones given there's
no assignment we want to supress warnings for.

Eheh sorry, should be a leftover, fixed.

quoted

+			pr_warn(" * %s: children of /cpus/idle-states must be \"arm,idle-state\" compatible\n",
+				     state_node->full_name);

Presumably the entire reason for having the compatible string is for
future extensibility.

It would probably be better to have something like:

	pr_warn("Node %s has unrecognised/missing compatible string\n",
		state_node->full_name);

It makes sense, so I will change the pr_warn.

quoted

+			continue;
+		}
+		/*
+		 * If memory allocation fails, better bail out.
+		 * Initialized nodes are freed at initialization
+		 * completion in of_init_idle_driver().
+		 */
+		if ((add_state_node(drv->cpumask, state_node) == -ENOMEM))
+			break;

Can we not return? Or is the list sort important in the error case too?

Well, we might have a valid list of states that have to be sorted and I
think that's correct to break and not just return in that case.

Let's see if I can avoid the sorting altogether.

quoted

+	}
+	/*
+	 * Sort the states list before initializing the CPUidle driver
+	 * states array.
+	 */
+	list_sort(NULL, &head, state_cmp);
+}
+
+/**
+ * dt_init_idle_driver() - Parse the DT idle states and initialize the
+ *			   idle driver states array
+ *
+ * @drv:	  Pointer to CPU idle driver to be initialized
+ * @state_nodes:  Array of struct device_nodes to be initialized if
+ *		  init_nodes == true. Must be sized CPUIDLE_STATE_MAX
+ * @start_idx:    First idle state index to be initialized
+ * @init_nodes:   Boolean to request device nodes initialization
+ *
+ * On success the states array in the cpuidle driver contains
+ * initialized entries in the states array, starting from index start_idx.
+ * If init_nodes == true, on success the state_nodes array is initialized
+ * with idle state DT node pointers, starting from index start_idx,
+ * in a 1:1 relation with the idle driver states array.
+ *
+ * Return:
+ *	0 on success
+ *	<0 on failure
+ */
+int __init dt_init_idle_driver(struct cpuidle_driver *drv,
+			       struct device_node *state_nodes[],
+			       unsigned int start_idx, bool init_nodes)
+{
+	struct device_node *idle_states_node;
+	int ret;
+
+	if (start_idx >= CPUIDLE_STATE_MAX) {
+		pr_warn("State index exceeds static CPU idle driver states array size\n");
+		return -EINVAL;
+	}
+
+	if (WARN(init_nodes && !state_nodes,
+		"Requested nodes stashing in an invalid nodes container\n"))
+		return -EINVAL;

That warning message is somewhat confusing, and I'm not sure I
follow the logic.

It is a belt and braces check to make sure that, if the dt init code is
requested to fill in the state_nodes array (init_nodes == true), at least
the array base was passed and it is not a NULL pointer. I think I'd better
remove it and let the kernel oops if the interface is used wrongly, that would
be a kernel bug and there is not much to WARN about.

Thanks,
Lorenzo