Re: [PATCH 2/5] drm: Add initial dnyamic power off feature

On Mon, Sep 10, 2012 at 02:31:52PM +1000, Dave Airlie wrote:

From: Dave Airlie airlied@redhat.com

For secondary GPUs in laptops, i.e. optimus or powerxpress, we have methods for powering down the GPU completely. This adds support to the drm core for powering back up the GPU on any access from ioctls or sysfs interfaces, and fires a 5s timer to test if we can power the GPU off.

This is just an initial implementation to get discussions started!

Signed-off-by: Dave Airlie airlied@redhat.com

drivers/gpu/drm/drm_drv.c | 68 +++++++++++++++++++++++++++++++++++++++++ drivers/gpu/drm/drm_fb_helper.c | 2 +- drivers/gpu/drm/drm_fops.c | 6 +++- drivers/gpu/drm/drm_stub.c | 1 + drivers/gpu/drm/drm_sysfs.c | 4 +++ include/drm/drmP.h | 9 ++++++ 6 files changed, 88 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/drm_drv.c b/drivers/gpu/drm/drm_drv.c index 9238de4..9fae62a 100644 --- a/drivers/gpu/drm/drm_drv.c +++ b/drivers/gpu/drm/drm_drv.c @@ -383,12 +383,17 @@ long drm_ioctl(struct file *filp, char stack_kdata[128]; char *kdata = NULL; unsigned int usize, asize;

• int ret;

  dev = file_priv->minor->dev;

  if (drm_device_is_unplugged(dev)) return -ENODEV;

• ret = drm_dynamic_power_wakeup(dev, __func__);

• if (ret)

• return ret;
  

• atomic_inc(&dev->ioctl_count); atomic_inc(&dev->counts[_DRM_STAT_IOCTLS]); ++file_priv->ioctl_count;

@@ -494,3 +499,66 @@ struct drm_local_map *drm_getsarea(struct drm_device *dev) return NULL; } EXPORT_SYMBOL(drm_getsarea);

+#define POWER_OFF_PERIOD (5*HZ)

+static void drm_dynamic_enable_poll(struct drm_device *dev) +{

• queue_delayed_work(system_nrt_wq, &dev->dynamic_power_poll, POWER_OFF_PERIOD);

+}

+static void drm_power_poll_execute(struct work_struct *work) +{

• struct delayed_work *delayed_work = to_delayed_work(work);
• struct drm_device *dev = container_of(delayed_work, struct drm_device, dynamic_power_poll);
• bool ret;
• /* ask driver if okay to power off */

My midlayer-smell-o-meter just cranked up to 11 when reading this comment ;-)

I'd have expected: - Drivers to check the power state and enable the gpu if it's off in their cs ioctl (instead of the brute-force every ioctl there is approach in the drm core) - Launch a delayed work item to cut the power again once they notice that the gpu is idle (dunno how radeon/nouveau work exactly, but i915 has this nice retire_requests work item which does a few similar things for power management, like lvds downclocking) - Same thing for any other kind of usage, like e.g. kms: Drivers can wrap the crtc helper set_mode to ensure the gpu is on and also check for any enabled outputs before launching the delayed power off switch. Same applies to any sysfs/debugfs files (although in the case of i915.ko, many of these don't need the hw to be on).

I guess you could add a small vga_switcheroo_dynamic_power_state struct or something with a few helpers to do that to extract some duplicated code from drivers. But tbh managing a piece of state lazily with a timer/delayed work item is a common code pattern, so I don't think even that little bit of code sharing is worth it.

Cheers, Daniel

PS: I've read a bit around in the switcheroo code and I think the switcheroo ->can_switch callback is actually worse ... since the drm drivers just check the open_count (which is hilariously racy in itself, too) and there's no locking to ensure that stays the same between the ->can_switch check and the actual ->set_state calls ...

/me needs morning coffee to think this through

• ret = dev->driver->dynamic_off_check(dev);
• if (ret == false)

• goto out_requeue;
  

• ret = dev->driver->dynamic_set_state(dev, DRM_SWITCH_POWER_DYNAMIC_OFF);
• DRM_INFO("powering down\n");
• return;

+out_requeue:

• queue_delayed_work(system_nrt_wq, delayed_work, POWER_OFF_PERIOD);

+}

+int drm_dynamic_power_wakeup(struct drm_device *dev, const char *reason) +{

• int ret;
• if (!dev->driver->dynamic_off_check)

• return 0;
  

• cancel_delayed_work_sync(&dev->dynamic_power_poll);
• ret = mutex_lock_interruptible(&dev->dynamic_power_lock);
• if (ret) {

• drm_dynamic_enable_poll(dev);
  

• return ret;
  

• }
• if (dev->switch_power_state != DRM_SWITCH_POWER_DYNAMIC_OFF) {

• mutex_unlock(&dev->dynamic_power_lock);
  

• drm_dynamic_enable_poll(dev);
  

• return 0;
  

• }
• DRM_INFO("waking up GPU for %s\n", reason);
• ret = dev->driver->dynamic_set_state(dev, DRM_SWITCH_POWER_ON);
• mutex_unlock(&dev->dynamic_power_lock);
• drm_dynamic_enable_poll(dev);
• return 0;

+} +EXPORT_SYMBOL(drm_dynamic_power_wakeup);

+void drm_dynamic_power_init(struct drm_device *dev) +{

• INIT_DELAYED_WORK(&dev->dynamic_power_poll, drm_power_poll_execute);
• if (dev->driver->dynamic_off_check)

• drm_dynamic_enable_poll(dev);
  

+} +EXPORT_SYMBOL(drm_dynamic_power_init); diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c index f546d1e..9a2c56b 100644 --- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -245,7 +245,7 @@ bool drm_fb_helper_force_kernel_mode(void) return false;

list_for_each_entry(helper, &kernel_fb_helper_list, kernel_fb_list) {

• if (helper->dev->switch_power_state == DRM_SWITCH_POWER_OFF)
  

• if (helper->dev->switch_power_state == DRM_SWITCH_POWER_OFF || helper->dev->switch_power_state == DRM_SWITCH_POWER_DYNAMIC_OFF)
  continue;
  
  

  ret = drm_fb_helper_restore_fbdev_mode(helper);

diff --git a/drivers/gpu/drm/drm_fops.c b/drivers/gpu/drm/drm_fops.c index 5062eec..285e53f 100644 --- a/drivers/gpu/drm/drm_fops.c +++ b/drivers/gpu/drm/drm_fops.c @@ -239,9 +239,13 @@ static int drm_open_helper(struct inode *inode, struct file *filp, return -EBUSY; /* No exclusive opens */ if (!drm_cpu_valid()) return -EINVAL;

• if (dev->switch_power_state != DRM_SWITCH_POWER_ON)

• if (dev->switch_power_state != DRM_SWITCH_POWER_ON && dev->switch_power_state != DRM_SWITCH_POWER_DYNAMIC_OFF) return -EINVAL;

• ret = drm_dynamic_power_wakeup(dev, __func__);

• if (ret)

• return ret;
  

• DRM_DEBUG("pid = %d, minor = %d\n", task_pid_nr(current), minor_id);

  priv = kzalloc(sizeof(*priv), GFP_KERNEL);

diff --git a/drivers/gpu/drm/drm_stub.c b/drivers/gpu/drm/drm_stub.c index 21bcd4a..0e56a40 100644 --- a/drivers/gpu/drm/drm_stub.c +++ b/drivers/gpu/drm/drm_stub.c @@ -273,6 +273,7 @@ int drm_fill_in_dev(struct drm_device *dev, spin_lock_init(&dev->event_lock); mutex_init(&dev->struct_mutex); mutex_init(&dev->ctxlist_mutex);

• mutex_init(&dev->dynamic_power_lock);

  if (drm_ht_create(&dev->map_hash, 12)) { return -ENOMEM;

diff --git a/drivers/gpu/drm/drm_sysfs.c b/drivers/gpu/drm/drm_sysfs.c index 45ac8d6..850c210 100644 --- a/drivers/gpu/drm/drm_sysfs.c +++ b/drivers/gpu/drm/drm_sysfs.c @@ -162,6 +162,10 @@ static ssize_t status_show(struct device *device, enum drm_connector_status status; int ret;

• ret = drm_dynamic_power_wakeup(connector->dev, __func__);
• if (ret)

• return ret;
  

• ret = mutex_lock_interruptible(&connector->dev->mode_config.mutex); if (ret) return ret;

diff --git a/include/drm/drmP.h b/include/drm/drmP.h index d6b67bb..65154b0 100644 --- a/include/drm/drmP.h +++ b/include/drm/drmP.h @@ -933,6 +933,9 @@ struct drm_driver { struct drm_device *dev, uint32_t handle);

• bool (*dynamic_off_check)(struct drm_device *dev);
• int (*dynamic_set_state)(struct drm_device *dev, int state);
• /* Driver private ops for this object */ const struct vm_operations_struct *gem_vm_ops;

@@ -1197,11 +1200,15 @@ struct drm_device { int switch_power_state;

atomic_t unplugged; /* device has been unplugged or gone away */

• struct delayed_work dynamic_power_poll;
• struct mutex dynamic_power_lock;

};

#define DRM_SWITCH_POWER_ON 0 #define DRM_SWITCH_POWER_OFF 1 #define DRM_SWITCH_POWER_CHANGING 2 +#define DRM_SWITCH_POWER_DYNAMIC_OFF 3

static __inline__ int drm_core_check_feature(struct drm_device *dev, int feature) @@ -1770,5 +1777,7 @@ static __inline__ bool drm_can_sleep(void) return true; }

+void drm_dynamic_power_init(struct drm_device *dev); +int drm_dynamic_power_wakeup(struct drm_device *dev, const char *reason); #endif /* __KERNEL__ */

#endif

1.7.12

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