linux-kernel - [PATCH] drm/vc4: Use runtime autosuspend to avoid thrashing V3D power state.

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Date:   Fri,  4 Nov 2016 16:32:38 -0700
From:   Eric Anholt <eric@...olt.net>
To:     dri-devel@...ts.freedesktop.org
Cc:     linux-kernel@...r.kernel.org, Eric Anholt <eric@...olt.net>
Subject: [PATCH] drm/vc4: Use runtime autosuspend to avoid thrashing V3D power state.

The pm_runtime_put() we were using immediately released power on the
device, which meant that we were generally turning the device off and
on once per frame.  In many profiles I've looked at, that added up to
about 1% of CPU time, but this could get worse in the case of frequent
rendering and readback (as may happen in X rendering).  By keeping the
device on until we've been idle for a couple of frames, we drop the
overhead of runtime PM down to sub-.1%.

Signed-off-by: Eric Anholt <eric@...olt.net>
---
 drivers/gpu/drm/vc4/vc4_drv.c | 9 ++++++---
 drivers/gpu/drm/vc4/vc4_gem.c | 6 ++++--
 drivers/gpu/drm/vc4/vc4_v3d.c | 2 ++
 3 files changed, 12 insertions(+), 5 deletions(-)

diff --git a/drivers/gpu/drm/vc4/vc4_drv.c b/drivers/gpu/drm/vc4/vc4_drv.c
index b087404c2784..7abfe088f2d1 100644
--- a/drivers/gpu/drm/vc4/vc4_drv.c
+++ b/drivers/gpu/drm/vc4/vc4_drv.c
@@ -61,21 +61,24 @@ static int vc4_get_param_ioctl(struct drm_device *dev, void *data,
 		if (ret < 0)
 			return ret;
 		args->value = V3D_READ(V3D_IDENT0);
-		pm_runtime_put(&vc4->v3d->pdev->dev);
+		pm_runtime_mark_last_busy(&vc4->v3d->pdev->dev);
+		pm_runtime_put_autosuspend(&vc4->v3d->pdev->dev);
 		break;
 	case DRM_VC4_PARAM_V3D_IDENT1:
 		ret = pm_runtime_get_sync(&vc4->v3d->pdev->dev);
 		if (ret < 0)
 			return ret;
 		args->value = V3D_READ(V3D_IDENT1);
-		pm_runtime_put(&vc4->v3d->pdev->dev);
+		pm_runtime_mark_last_busy(&vc4->v3d->pdev->dev);
+		pm_runtime_put_autosuspend(&vc4->v3d->pdev->dev);
 		break;
 	case DRM_VC4_PARAM_V3D_IDENT2:
 		ret = pm_runtime_get_sync(&vc4->v3d->pdev->dev);
 		if (ret < 0)
 			return ret;
 		args->value = V3D_READ(V3D_IDENT2);
-		pm_runtime_put(&vc4->v3d->pdev->dev);
+		pm_runtime_mark_last_busy(&vc4->v3d->pdev->dev);
+		pm_runtime_put_autosuspend(&vc4->v3d->pdev->dev);
 		break;
 	case DRM_VC4_PARAM_SUPPORTS_BRANCHES:
 	case DRM_VC4_PARAM_SUPPORTS_ETC1:
diff --git a/drivers/gpu/drm/vc4/vc4_gem.c b/drivers/gpu/drm/vc4/vc4_gem.c
index 303f23c96220..db920771bfb5 100644
--- a/drivers/gpu/drm/vc4/vc4_gem.c
+++ b/drivers/gpu/drm/vc4/vc4_gem.c
@@ -709,8 +709,10 @@ vc4_complete_exec(struct drm_device *dev, struct vc4_exec_info *exec)
 	}
 
 	mutex_lock(&vc4->power_lock);
-	if (--vc4->power_refcount == 0)
-		pm_runtime_put(&vc4->v3d->pdev->dev);
+	if (--vc4->power_refcount == 0) {
+		pm_runtime_mark_last_busy(&vc4->v3d->pdev->dev);
+		pm_runtime_put_autosuspend(&vc4->v3d->pdev->dev);
+	}
 	mutex_unlock(&vc4->power_lock);
 
 	kfree(exec);
diff --git a/drivers/gpu/drm/vc4/vc4_v3d.c b/drivers/gpu/drm/vc4/vc4_v3d.c
index e6d3c6028341..7cc346ad9b0b 100644
--- a/drivers/gpu/drm/vc4/vc4_v3d.c
+++ b/drivers/gpu/drm/vc4/vc4_v3d.c
@@ -222,6 +222,8 @@ static int vc4_v3d_bind(struct device *dev, struct device *master, void *data)
 		return ret;
 	}
 
+	pm_runtime_use_autosuspend(dev);
+	pm_runtime_set_autosuspend_delay(dev, 40); /* a little over 2 frames. */
 	pm_runtime_enable(dev);
 
 	return 0;
-- 
2.10.2