Re: [PATCH 05/15] drm/panfrost: use spinlock instead of atomic

[Steven Price]

On 10/05/2020 17:55, Clément Péron wrote:

Convert busy_count to a simple int protected by spinlock.

Signed-off-by: Clément Péron <peron.c...@gmail.com>

Looks like a fairly mechanical cleanup.

Reviewed-by: Steven Price <steven.pr...@arm.com>

---
  drivers/gpu/drm/panfrost/panfrost_devfreq.c | 43 +++++++++++++++------
  drivers/gpu/drm/panfrost/panfrost_devfreq.h | 10 ++++-
  2 files changed, 41 insertions(+), 12 deletions(-)

diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.c 
b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
index 962550363391..78753cfb59fb 100644
--- a/drivers/gpu/drm/panfrost/panfrost_devfreq.c
+++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.c
@@ -12,16 +12,12 @@

static void panfrost_devfreq_update_utilization(struct panfrost_devfreq *pfdevfreq)

  {
-       ktime_t now;
-       ktime_t last;
-
-       if (!pfdevfreq->devfreq)
-               return;
+       ktime_t now, last;

now = ktime_get();

        last = pfdevfreq->time_last_update;

- if (atomic_read(&pfdevfreq->busy_count) > 0)

+       if (pfdevfreq->busy_count > 0)
                pfdevfreq->busy_time += ktime_sub(now, last);
        else
                pfdevfreq->idle_time += ktime_sub(now, last);
@@ -59,10 +55,14 @@ static int panfrost_devfreq_get_dev_status(struct device 
*dev,
  {
        struct panfrost_device *pfdev = dev_get_drvdata(dev);
        struct panfrost_devfreq *pfdevfreq = &pfdev->pfdevfreq;
+       unsigned long irqflags;
+
+       status->current_frequency = clk_get_rate(pfdev->clock);
+
+       spin_lock_irqsave(&pfdevfreq->lock, irqflags);

panfrost_devfreq_update_utilization(pfdevfreq); - status->current_frequency = clk_get_rate(pfdev->clock);

        status->total_time = ktime_to_ns(ktime_add(pfdevfreq->busy_time,
                                                   pfdevfreq->idle_time));

@@ -70,6 +70,8 @@ static int panfrost_devfreq_get_dev_status(struct device *dev, panfrost_devfreq_reset(pfdevfreq); + spin_unlock_irqrestore(&pfdevfreq->lock, irqflags);

+
        dev_dbg(pfdev->dev, "busy %lu total %lu %lu %% freq %lu MHz\n",
                status->busy_time, status->total_time,
                status->busy_time / (status->total_time / 100),
@@ -100,6 +102,8 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
        else if (ret)
                return ret;

+ spin_lock_init(&pfdevfreq->lock);

+
        panfrost_devfreq_reset(pfdevfreq);

cur_freq = clk_get_rate(pfdev->clock);

@@ -162,15 +166,32 @@ void panfrost_devfreq_suspend(struct panfrost_device 
*pfdev)

void panfrost_devfreq_record_busy(struct panfrost_devfreq *pfdevfreq)

  {
+       unsigned long irqflags;
+
+       if (!pfdevfreq->devfreq)
+               return;
+
+       spin_lock_irqsave(&pfdevfreq->lock, irqflags);
+
        panfrost_devfreq_update_utilization(pfdevfreq);
-       atomic_inc(&pfdevfreq->busy_count);
+
+       pfdevfreq->busy_count++;
+
+       spin_unlock_irqrestore(&pfdevfreq->lock, irqflags);
  }

void panfrost_devfreq_record_idle(struct panfrost_devfreq *pfdevfreq)

  {
-       int count;
+       unsigned long irqflags;
+
+       if (!pfdevfreq->devfreq)
+               return;
+
+       spin_lock_irqsave(&pfdevfreq->lock, irqflags);

panfrost_devfreq_update_utilization(pfdevfreq);

-       count = atomic_dec_if_positive(&pfdevfreq->busy_count);
-       WARN_ON(count < 0);
+
+       WARN_ON(--pfdevfreq->busy_count < 0);
+
+       spin_unlock_irqrestore(&pfdevfreq->lock, irqflags);
  }
diff --git a/drivers/gpu/drm/panfrost/panfrost_devfreq.h 
b/drivers/gpu/drm/panfrost/panfrost_devfreq.h
index 0697f8d5aa34..e6629900a618 100644
--- a/drivers/gpu/drm/panfrost/panfrost_devfreq.h
+++ b/drivers/gpu/drm/panfrost/panfrost_devfreq.h
@@ -4,6 +4,7 @@
  #ifndef __PANFROST_DEVFREQ_H__
  #define __PANFROST_DEVFREQ_H__

+#include <linux/spinlock.h>

  #include <linux/ktime.h>

struct devfreq;

@@ -14,10 +15,17 @@ struct panfrost_device;
  struct panfrost_devfreq {
        struct devfreq *devfreq;
        struct thermal_cooling_device *cooling;
+
        ktime_t busy_time;
        ktime_t idle_time;
        ktime_t time_last_update;
-       atomic_t busy_count;
+       int busy_count;
+       /*
+        * Protect busy_time, idle_time, time_last_update and busy_count
+        * because these can be updated concurrently, for example by the GP
+        * and PP interrupts.
+        */
+       spinlock_t lock;
  };

int panfrost_devfreq_init(struct panfrost_device *pfdev);