drm/panfrost: Select devfreq

Currently, there is some logic for the driver to work without devfreq.
However, the driver actually fails to probe if !CONFIG_PM_DEVFREQ.

Fix this by selecting devfreq, and drop the additional checks
for devfreq.
Signed-off-by: Ezequiel Garcia <ezequiel@collabora.com>
Signed-off-by: Rob Herring <robh@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190517150042.776-1-ezequiel@collabora.com

drivers/gpu/drm/panfrost/Kconfig

@@ -9,6 +9,7 @@ config DRM_PANFROST
 	select IOMMU_SUPPORT
 	select IOMMU_IO_PGTABLE_LPAE
 	select DRM_GEM_SHMEM_HELPER
+	select PM_DEVFREQ
 	help
 	  DRM driver for ARM Mali Midgard (T6xx, T7xx, T8xx) and
 	  Bifrost (G3x, G5x, G7x) GPUs.

drivers/gpu/drm/panfrost/panfrost_devfreq.c

@@ -140,8 +140,8 @@ int panfrost_devfreq_init(struct panfrost_device *pfdev)
 		return 0;
 
 	ret = dev_pm_opp_of_add_table(&pfdev->pdev->dev);
-	if (ret == -ENODEV) /* Optional, continue without devfreq */
-		return 0;
+	if (ret)
+		return ret;
 
 	panfrost_devfreq_reset(pfdev);
 
@@ -170,9 +170,6 @@ void panfrost_devfreq_resume(struct panfrost_device *pfdev)
 {
 	int i;
 
-	if (!pfdev->devfreq.devfreq)
-		return;
-
 	panfrost_devfreq_reset(pfdev);
 	for (i = 0; i < NUM_JOB_SLOTS; i++)
 		pfdev->devfreq.slot[i].busy = false;
@@ -182,9 +179,6 @@ void panfrost_devfreq_resume(struct panfrost_device *pfdev)
 
 void panfrost_devfreq_suspend(struct panfrost_device *pfdev)
 {
-	if (!pfdev->devfreq.devfreq)
-		return;
-
 	devfreq_suspend_device(pfdev->devfreq.devfreq);
 }
 
@@ -194,9 +188,6 @@ static void panfrost_devfreq_update_utilization(struct panfrost_device *pfdev, i
 	ktime_t now;
 	ktime_t last;
 
-	if (!pfdev->devfreq.devfreq)
-		return;
-
 	now = ktime_get();
 	last = pfdev->devfreq.slot[slot].time_last_update;