drm: Extend framebuffer_check to handle formats with cpp/char_per_block 0

For formats that are supported only with non-linear modifiers it
doesn't make to much sense to define cpp or char_per_block, so that
will be set to 0.

This patch adds a restriction to force having a modifier attached when
cpp/char_per_block is 0, and to bypass checking the pitch restriction.

This had been discussed here.
[1] https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&highlight_names=&date=2018-09-13&show_html=trueReviewed-by: Brian Starkey <brian.starkey@arm.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Alexandru Gheorghe <alexandru-cosmin.gheorghe@arm.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181101151051.1509-5-alexandru-cosmin.gheorghe@arm.com

drivers/gpu/drm/drm_framebuffer.c

@@ -195,8 +195,14 @@ static int framebuffer_check(struct drm_device *dev,
 	for (i = 0; i < info->num_planes; i++) {
 		unsigned int width = fb_plane_width(r->width, info, i);
 		unsigned int height = fb_plane_height(r->height, info, i);
+		unsigned int block_size = info->char_per_block[i];
 		u64 min_pitch = drm_format_info_min_pitch(info, i, width);
 
+		if (!block_size && (r->modifier[i] == DRM_FORMAT_MOD_LINEAR)) {
+			DRM_DEBUG_KMS("Format requires non-linear modifier for plane %d\n", i);
+			return -EINVAL;
+		}
+
 		if (!r->handles[i]) {
 			DRM_DEBUG_KMS("no buffer object handle for plane %d\n", i);
 			return -EINVAL;
@@ -208,7 +214,7 @@ static int framebuffer_check(struct drm_device *dev,
 		if ((uint64_t) height * r->pitches[i] + r->offsets[i] > UINT_MAX)
 			return -ERANGE;
 
-		if (r->pitches[i] < min_pitch) {
+		if (block_size && r->pitches[i] < min_pitch) {
 			DRM_DEBUG_KMS("bad pitch %u for plane %d\n", r->pitches[i], i);
 			return -EINVAL;
 		}