drm/tegra: dsi: Enhance runtime power management

The MIPI DSI output on Tegra SoCs requires some external logic to
calibrate the MIPI pads before a video signal can be transmitted. This
MIPI calibration logic requires to be powered on while the MIPI pads are
being used, which is currently done as part of the DSI driver's probe
implementation.

This is suboptimal because it will leave the MIPI calibration logic
powered up even if the DSI output is never used.

On Tegra114 and earlier this behaviour also causes the driver to hang
while trying to power up the MIPI calibration logic because the power
partition that contains the MIPI calibration logic will be powered on
by the display controller at output pipeline configuration time. Thus
the power up sequence for the MIPI calibration logic happens before
it's power partition is guaranteed to be enabled.

Fix this by splitting up the API into a request/free pair of functions
that manage the runtime dependency between the DSI and the calibration
modules (no registers are accessed) and a set of enable, calibrate and
disable functions that program the MIPI calibration logic at points in
time where the power partition is really enabled.

While at it, make sure that the runtime power management also works in
ganged mode, which is currently also broken.

Reported-by: Jonathan Hunter <jonathanh@nvidia.com>
Tested-by: Jonathan Hunter <jonathanh@nvidia.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>

drivers/gpu/drm/tegra/dsi.c

@@ -840,6 +840,21 @@ static const struct drm_encoder_funcs tegra_dsi_encoder_funcs = {
 	.destroy = tegra_output_encoder_destroy,
 };
 
+static void tegra_dsi_unprepare(struct tegra_dsi *dsi)
+{
+	int err;
+
+	if (dsi->slave)
+		tegra_dsi_unprepare(dsi->slave);
+
+	err = tegra_mipi_disable(dsi->mipi);
+	if (err < 0)
+		dev_err(dsi->dev, "failed to disable MIPI calibration: %d\n",
+			err);
+
+	pm_runtime_put(dsi->dev);
+}
+
 static void tegra_dsi_encoder_disable(struct drm_encoder *encoder)
 {
 	struct tegra_output *output = encoder_to_output(encoder);
@@ -876,7 +891,26 @@ static void tegra_dsi_encoder_disable(struct drm_encoder *encoder)
 
 	tegra_dsi_disable(dsi);
 
-	pm_runtime_put(dsi->dev);
+	tegra_dsi_unprepare(dsi);
+}
+
+static void tegra_dsi_prepare(struct tegra_dsi *dsi)
+{
+	int err;
+
+	pm_runtime_get_sync(dsi->dev);
+
+	err = tegra_mipi_enable(dsi->mipi);
+	if (err < 0)
+		dev_err(dsi->dev, "failed to enable MIPI calibration: %d\n",
+			err);
+
+	err = tegra_dsi_pad_calibrate(dsi);
+	if (err < 0)
+		dev_err(dsi->dev, "MIPI calibration failed: %d\n", err);
+
+	if (dsi->slave)
+		tegra_dsi_prepare(dsi->slave);
 }
 
 static void tegra_dsi_encoder_enable(struct drm_encoder *encoder)
@@ -887,13 +921,8 @@ static void tegra_dsi_encoder_enable(struct drm_encoder *encoder)
 	struct tegra_dsi *dsi = to_dsi(output);
 	struct tegra_dsi_state *state;
 	u32 value;
-	int err;
-
-	pm_runtime_get_sync(dsi->dev);
 
-	err = tegra_dsi_pad_calibrate(dsi);
-	if (err < 0)
-		dev_err(dsi->dev, "MIPI calibration failed: %d\n", err);
+	tegra_dsi_prepare(dsi);
 
 	state = tegra_dsi_get_state(dsi);
 

drivers/gpu/host1x/mipi.c

@@ -242,20 +242,6 @@ struct tegra_mipi_device *tegra_mipi_request(struct device *device)
 	dev->pads = args.args[0];
 	dev->device = device;
 
-	mutex_lock(&dev->mipi->lock);
-
-	if (dev->mipi->usage_count++ == 0) {
-		err = tegra_mipi_power_up(dev->mipi);
-		if (err < 0) {
-			dev_err(dev->mipi->dev,
-				"failed to power up MIPI bricks: %d\n",
-				err);
-			return ERR_PTR(err);
-		}
-	}
-
-	mutex_unlock(&dev->mipi->lock);
-
 	return dev;
 
 put:
@@ -270,29 +256,42 @@ EXPORT_SYMBOL(tegra_mipi_request);
 
 void tegra_mipi_free(struct tegra_mipi_device *device)
 {
-	int err;
+	platform_device_put(device->pdev);
+	kfree(device);
+}
+EXPORT_SYMBOL(tegra_mipi_free);
 
-	mutex_lock(&device->mipi->lock);
+int tegra_mipi_enable(struct tegra_mipi_device *dev)
+{
+	int err = 0;
 
-	if (--device->mipi->usage_count == 0) {
-		err = tegra_mipi_power_down(device->mipi);
-		if (err < 0) {
-			/*
-			 * Not much that can be done here, so an error message
-			 * will have to do.
-			 */
-			dev_err(device->mipi->dev,
-				"failed to power down MIPI bricks: %d\n",
-				err);
-		}
-	}
+	mutex_lock(&dev->mipi->lock);
 
-	mutex_unlock(&device->mipi->lock);
+	if (dev->mipi->usage_count++ == 0)
+		err = tegra_mipi_power_up(dev->mipi);
+
+	mutex_unlock(&dev->mipi->lock);
+
+	return err;
 
-	platform_device_put(device->pdev);
-	kfree(device);
 }
-EXPORT_SYMBOL(tegra_mipi_free);
+EXPORT_SYMBOL(tegra_mipi_enable);
+
+int tegra_mipi_disable(struct tegra_mipi_device *dev)
+{
+	int err = 0;
+
+	mutex_lock(&dev->mipi->lock);
+
+	if (--dev->mipi->usage_count == 0)
+		err = tegra_mipi_power_down(dev->mipi);
+
+	mutex_unlock(&dev->mipi->lock);
+
+	return err;
+
+}
+EXPORT_SYMBOL(tegra_mipi_disable);
 
 static int tegra_mipi_wait(struct tegra_mipi *mipi)
 {

include/linux/host1x.h

@@ -304,6 +304,8 @@ struct tegra_mipi_device;
 
 struct tegra_mipi_device *tegra_mipi_request(struct device *device);
 void tegra_mipi_free(struct tegra_mipi_device *device);
+int tegra_mipi_enable(struct tegra_mipi_device *device);
+int tegra_mipi_disable(struct tegra_mipi_device *device);
 int tegra_mipi_calibrate(struct tegra_mipi_device *device);
 
 #endif