[PATCH 3/3] drm/omap: Filter displays mode based on bandwidth limit

[Peter Ujfalusi]

If we have memory bandwidth limit configured, reject the modes which would
require more bandwidth than the limit if it is used with one full
resolution plane (most common use case).

This filtering is not providing full protection as it is possible that
application would pick smaller crtc resolution with high resolution planes
and down scaling, or can enable more smaller planes where the sum of their
bandwidth need would be higher than the limit.

This patch only allows us to filter out modes which would need more
bandwidth if they were used with one full screen plane.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi at ti.com>
---
 drivers/gpu/drm/omapdrm/omap_connector.c | 24 ++++++++++++++++++++++++
 drivers/gpu/drm/omapdrm/omap_drv.c       |  5 +++++
 drivers/gpu/drm/omapdrm/omap_drv.h       |  3 +++
 3 files changed, 32 insertions(+)

diff --git a/drivers/gpu/drm/omapdrm/omap_connector.c b/drivers/gpu/drm/omapdrm/omap_connector.c
index aa5ba9ae2191..c693d22960c8 100644
--- a/drivers/gpu/drm/omapdrm/omap_connector.c
+++ b/drivers/gpu/drm/omapdrm/omap_connector.c
@@ -159,6 +159,7 @@ static int omap_connector_mode_valid(struct drm_connector *connector,
 				 struct drm_display_mode *mode)
 {
 	struct omap_connector *omap_connector = to_omap_connector(connector);
+	struct omap_drm_private *priv = connector->dev->dev_private;
 	struct omap_dss_device *dssdev = omap_connector->dssdev;
 	struct omap_dss_driver *dssdrv = dssdev->driver;
 	struct videomode vm = {0};
@@ -203,6 +204,29 @@ static int omap_connector_mode_valid(struct drm_connector *connector,
 		drm_mode_destroy(dev, new_mode);
 	}
 
+	/* Check for bandwidth limit */
+	if (!r && priv->max_bandwidth) {
+		unsigned int bandwidth, real_refresh;
+
+		/*
+		 * Estimation for the bandwidth need of a given mode with one
+		 * full screen plane:
+		 * resolution * 32bpp * (real) refresh rate
+		 */
+		real_refresh = drm_mode_vrefresh(mode);
+		if (mode->flags & DRM_MODE_FLAG_INTERLACE)
+			real_refresh /= 2;
+
+		bandwidth = vm.hactive * vm.vactive * 4 * real_refresh;
+
+		/*
+		 * Reject modes which would need more bandwidth if used with one
+		 * full resolution plane (most common use case).
+		 */
+		if (priv->max_bandwidth < bandwidth)
+			ret = MODE_BAD;
+	}
+
 	DBG("connector: mode %s: "
 			"%d:\"%s\" %d %d %d %d %d %d %d %d %d %d 0x%x 0x%x",
 			(ret == MODE_OK) ? "valid" : "invalid",
diff --git a/drivers/gpu/drm/omapdrm/omap_drv.c b/drivers/gpu/drm/omapdrm/omap_drv.c
index 528cf5c25bec..58b4a0e149e0 100644
--- a/drivers/gpu/drm/omapdrm/omap_drv.c
+++ b/drivers/gpu/drm/omapdrm/omap_drv.c
@@ -701,6 +701,11 @@ static int pdev_probe(struct platform_device *pdev)
 	spin_lock_init(&priv->list_lock);
 	INIT_LIST_HEAD(&priv->obj_list);
 
+	/* Get memory bandwidth limits */
+	if (priv->dispc_ops->get_memory_bandwidth_limit)
+		priv->max_bandwidth =
+				priv->dispc_ops->get_memory_bandwidth_limit();
+
 	omap_gem_init(ddev);
 
 	ret = omap_modeset_init(ddev);
diff --git a/drivers/gpu/drm/omapdrm/omap_drv.h b/drivers/gpu/drm/omapdrm/omap_drv.h
index cccaae787a7c..d49715272080 100644
--- a/drivers/gpu/drm/omapdrm/omap_drv.h
+++ b/drivers/gpu/drm/omapdrm/omap_drv.h
@@ -86,6 +86,9 @@ struct omap_drm_private {
 	spinlock_t wait_lock;		/* protects the wait_list */
 	struct list_head wait_list;	/* list of omap_irq_wait */
 	uint32_t irq_mask;		/* enabled irqs in addition to wait_list */
+
+	/* memory bandwidth limit if it is needed on the platform */
+	unsigned int max_bandwidth;
 };
 
 
-- 
Peter

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