[PATCH 2/2] drm/msm/devfreq: Add 1ms delay before clamping freq

[Rob Clark]

From: Rob Clark <robdclark at chromium.org>

Add a short delay before clamping to idle frequency on active->idle
transition.  It takes ~0.5ms to increase the freq again on the next
idle->active transition, so this helps avoid extra freq transitions
on workloads that bounce between CPU and GPU.

Signed-off-by: Rob Clark <robdclark at chromium.org>
---
Note that this sort of re-introduces the theoretical race solved
by [1].. but that should not be a problem with something along the
lines of [2]. 

[1] https://patchwork.freedesktop.org/patch/455910/?series=95111&rev=1
[2] https://patchwork.freedesktop.org/patch/455928/?series=95119&rev=1

 drivers/gpu/drm/msm/msm_gpu.h         |  7 +++++
 drivers/gpu/drm/msm/msm_gpu_devfreq.c | 38 +++++++++++++++++++++------
 2 files changed, 37 insertions(+), 8 deletions(-)

diff --git a/drivers/gpu/drm/msm/msm_gpu.h b/drivers/gpu/drm/msm/msm_gpu.h
index 32a859307e81..2fcb6c195865 100644
--- a/drivers/gpu/drm/msm/msm_gpu.h
+++ b/drivers/gpu/drm/msm/msm_gpu.h
@@ -120,6 +120,13 @@ struct msm_gpu_devfreq {
 	 * it is inactive.
 	 */
 	unsigned long idle_freq;
+
+	/**
+	 * idle_work:
+	 *
+	 * Used to delay clamping to idle freq on active->idle transition.
+	 */
+	struct msm_hrtimer_work idle_work;
 };
 
 struct msm_gpu {
diff --git a/drivers/gpu/drm/msm/msm_gpu_devfreq.c b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
index 15b64f35c0f6..36e1930ee26d 100644
--- a/drivers/gpu/drm/msm/msm_gpu_devfreq.c
+++ b/drivers/gpu/drm/msm/msm_gpu_devfreq.c
@@ -96,8 +96,12 @@ static struct devfreq_dev_profile msm_devfreq_profile = {
 	.get_cur_freq = msm_devfreq_get_cur_freq,
 };
 
+static void msm_devfreq_idle_work(struct kthread_work *work);
+
 void msm_devfreq_init(struct msm_gpu *gpu)
 {
+	struct msm_gpu_devfreq *df = &gpu->devfreq;
+
 	/* We need target support to do devfreq */
 	if (!gpu->funcs->gpu_busy)
 		return;
@@ -113,25 +117,27 @@ void msm_devfreq_init(struct msm_gpu *gpu)
 	msm_devfreq_profile.freq_table = NULL;
 	msm_devfreq_profile.max_state = 0;
 
-	gpu->devfreq.devfreq = devm_devfreq_add_device(&gpu->pdev->dev,
+	df->devfreq = devm_devfreq_add_device(&gpu->pdev->dev,
 			&msm_devfreq_profile, DEVFREQ_GOV_SIMPLE_ONDEMAND,
 			NULL);
 
-	if (IS_ERR(gpu->devfreq.devfreq)) {
+	if (IS_ERR(df->devfreq)) {
 		DRM_DEV_ERROR(&gpu->pdev->dev, "Couldn't initialize GPU devfreq\n");
-		gpu->devfreq.devfreq = NULL;
+		df->devfreq = NULL;
 		return;
 	}
 
-	devfreq_suspend_device(gpu->devfreq.devfreq);
+	devfreq_suspend_device(df->devfreq);
 
-	gpu->cooling = of_devfreq_cooling_register(gpu->pdev->dev.of_node,
-			gpu->devfreq.devfreq);
+	gpu->cooling = of_devfreq_cooling_register(gpu->pdev->dev.of_node, df->devfreq);
 	if (IS_ERR(gpu->cooling)) {
 		DRM_DEV_ERROR(&gpu->pdev->dev,
 				"Couldn't register GPU cooling device\n");
 		gpu->cooling = NULL;
 	}
+
+	msm_hrtimer_work_init(&df->idle_work, gpu->worker, msm_devfreq_idle_work,
+			      CLOCK_MONOTONIC, HRTIMER_MODE_REL);
 }
 
 void msm_devfreq_cleanup(struct msm_gpu *gpu)
@@ -179,6 +185,11 @@ void msm_devfreq_active(struct msm_gpu *gpu)
 	unsigned int idle_time;
 	unsigned long target_freq = df->idle_freq;
 
+	/*
+	 * Cancel any pending transition to idle frequency:
+	 */
+	hrtimer_cancel(&df->idle_work.timer);
+
 	/*
 	 * Hold devfreq lock to synchronize with get_dev_status()/
 	 * target() callbacks
@@ -209,9 +220,12 @@ void msm_devfreq_active(struct msm_gpu *gpu)
 	mutex_unlock(&df->devfreq->lock);
 }
 
-void msm_devfreq_idle(struct msm_gpu *gpu)
+
+static void msm_devfreq_idle_work(struct kthread_work *work)
 {
-	struct msm_gpu_devfreq *df = &gpu->devfreq;
+	struct msm_gpu_devfreq *df = container_of(work,
+			struct msm_gpu_devfreq, idle_work.work);
+	struct msm_gpu *gpu = container_of(df, struct msm_gpu, devfreq);
 	unsigned long idle_freq, target_freq = 0;
 
 	/*
@@ -229,3 +243,11 @@ void msm_devfreq_idle(struct msm_gpu *gpu)
 
 	mutex_unlock(&df->devfreq->lock);
 }
+
+void msm_devfreq_idle(struct msm_gpu *gpu)
+{
+	struct msm_gpu_devfreq *df = &gpu->devfreq;
+
+	msm_hrtimer_queue_work(&df->idle_work, ms_to_ktime(1),
+			       HRTIMER_MODE_ABS);
+}
-- 
2.31.1