drm: add some caps for userspace to discover more info for dumb KMS driver (v2)

For the simple KMS driver case we need some more info about what the preferred
depth and if a shadow framebuffer is preferred.

I've only added this for intel/radeon which support the dumb ioctls so far.

If you need something really fancy you should be writing a real X.org driver.

v2: drop cursor information, just return an error from the cursor ioctls
and we can make userspace fallback to sw cursor in that case, cursor
info was getting too messy, best to start smaller.
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/drm_ioctl.c

@@ -277,6 +277,12 @@ int drm_getcap(struct drm_device *dev, void *data, struct drm_file *file_priv)
 	case DRM_CAP_VBLANK_HIGH_CRTC:
 		req->value = 1;
 		break;
+	case DRM_CAP_DUMB_PREFERRED_DEPTH:
+		req->value = dev->mode_config.preferred_depth;
+		break;
+	case DRM_CAP_DUMB_PREFER_SHADOW:
+		req->value = dev->mode_config.prefer_shadow;
+		break;
 	default:
 		return -EINVAL;
 	}

drivers/gpu/drm/i915/intel_display.c

@@ -9089,6 +9089,9 @@ void intel_modeset_init(struct drm_device *dev)
 	dev->mode_config.min_width = 0;
 	dev->mode_config.min_height = 0;
 
+	dev->mode_config.preferred_depth = 24;
+	dev->mode_config.prefer_shadow = 1;
+
 	dev->mode_config.funcs = (void *)&intel_mode_funcs;
 
 	intel_init_quirks(dev);

drivers/gpu/drm/radeon/radeon_display.c

@@ -1240,6 +1240,9 @@ int radeon_modeset_init(struct radeon_device *rdev)
 		rdev->ddev->mode_config.max_height = 4096;
 	}
 
+	rdev->ddev->mode_config.preferred_depth = 24;
+	rdev->ddev->mode_config.prefer_shadow = 1;
+
 	rdev->ddev->mode_config.fb_base = rdev->mc.aper_base;
 
 	ret = radeon_modeset_create_props(rdev);

include/drm/drm.h

@@ -761,6 +761,8 @@ struct drm_event_vblank {
 
 #define DRM_CAP_DUMB_BUFFER 0x1
 #define DRM_CAP_VBLANK_HIGH_CRTC 0x2
+#define DRM_CAP_DUMB_PREFERRED_DEPTH 0x3
+#define DRM_CAP_DUMB_PREFER_SHADOW 0x4
 
 /* typedef area */
 #ifndef __KERNEL__

include/drm/drm_crtc.h

@@ -796,6 +796,9 @@ struct drm_mode_config {
 	struct drm_property *scaling_mode_property;
 	struct drm_property *dithering_mode_property;
 	struct drm_property *dirty_info_property;
+
+	/* dumb ioctl parameters */
+	uint32_t preferred_depth, prefer_shadow;
 };
 
 #define obj_to_crtc(x) container_of(x, struct drm_crtc, base)