drm/tilcdc: adding some more devicetree config

Adding support for max-pixelclock and max-width device tree
entries. As some devices that use the tilcdc hardware module
have restrictions on the allowed/tested values. Also update DT
bindings document to reflect new parameters.

Signed-off-by: Darren Etheridge <[e-mail]>
Acked-by: Rob Clark <[e-mail]>
Signed-off-by: Dave Airlie <[e-mail]>

Documentation/devicetree/bindings/drm/tilcdc/tilcdc.txt

···
    services interrupts for this device.
  - ti,hwmods: Name of the hwmod associated to the LCDC
 
+Optional properties:
+ - max-bandwidth: The maximum pixels per second that the memory
+   interface / lcd controller combination can sustain
+ - max-width: The maximum horizontal pixel width supported by
+   the lcd controller.
+ - max-pixelclock: The maximum pixel clock that can be supported
+   by the lcd controller in KHz.
+
 Example:
 
 	fb: fb@4830e000 {

drivers/gpu/drm/tilcdc/tilcdc_crtc.c

···
 	if (mode->vdisplay > 2048)
 		return MODE_VIRTUAL_Y;
 
+	/*
+	 * some devices have a maximum allowed pixel clock
+	 * configured from the DT
+	 */
+	if (mode->clock > priv->max_pixelclock) {
+		DBG("Pruning mode, pixel clock too high");
+		return MODE_CLOCK_HIGH;
+	}
+
+	/*
+	 * some devices further limit the max horizontal resolution
+	 * configured from the DT
+	 */
+	if (mode->hdisplay > priv->max_width)
+		return MODE_BAD_WIDTH;
+
 	/* filter out modes that would require too much memory bandwidth: */
-	bandwidth = mode->hdisplay * mode->vdisplay * drm_mode_vrefresh(mode);
-	if (bandwidth > priv->max_bandwidth)
+	bandwidth = mode->hdisplay * mode->vdisplay *
+		drm_mode_vrefresh(mode);
+	if (bandwidth > priv->max_bandwidth) {
+		DBG("Pruning mode, exceeds defined bandwidth limit");
 		return MODE_BAD;
+	}
 
 	return MODE_OK;
 }

drivers/gpu/drm/tilcdc/tilcdc_drv.c

···
 #endif
 
 	if (of_property_read_u32(node, "max-bandwidth", &priv->max_bandwidth))
-		priv->max_bandwidth = 1280 * 1024 * 60;
+		priv->max_bandwidth = TILCDC_DEFAULT_MAX_BANDWIDTH;
+
+	DBG("Maximum Bandwidth Value %d", priv->max_bandwidth);
+
+	if (of_property_read_u32(node, "ti,max-width", &priv->max_width))
+		priv->max_width = TILCDC_DEFAULT_MAX_WIDTH;
+
+	DBG("Maximum Horizontal Pixel Width Value %dpixels", priv->max_width);
+
+	if (of_property_read_u32(node, "ti,max-pixelclock",
+					&priv->max_pixelclock))
+		priv->max_pixelclock = TILCDC_DEFAULT_MAX_PIXELCLOCK;
+
+	DBG("Maximum Pixel Clock Value %dKHz", priv->max_pixelclock);
 
 	pm_runtime_enable(dev->dev);
 

drivers/gpu/drm/tilcdc/tilcdc_drv.h

···
 #include <drm/drm_gem_cma_helper.h>
 #include <drm/drm_fb_cma_helper.h>
 
+/* Defaulting to pixel clock defined on AM335x */
+#define TILCDC_DEFAULT_MAX_PIXELCLOCK  126000
+/* Defaulting to max width as defined on AM335x */
+#define TILCDC_DEFAULT_MAX_WIDTH  2048
+/*
+ * This may need some tweaking, but want to allow at least 1280x1024@60
+ * with optimized DDR & EMIF settings tweaked 1920x1080@24 appears to
+ * be supportable
+ */
+#define TILCDC_DEFAULT_MAX_BANDWIDTH  (1280*1024*60)
+
+
 struct tilcdc_drm_private {
 	void __iomem *mmio;
 
···
 
 	/* don't attempt resolutions w/ higher W * H * Hz: */
 	uint32_t max_bandwidth;
+	/*
+	 * Pixel Clock will be restricted to some value as
+	 * defined in the device datasheet measured in KHz
+	 */
+	uint32_t max_pixelclock;
+	/*
+	 * Max allowable width is limited on a per device basis
+	 * measured in pixels
+	 */
+	uint32_t max_width;
 
 	/* register contents saved across suspend/resume: */
 	u32 saved_register[12];