drm/omap: handle incompatible buffer stride and pixel size

omapdrm doesn't check if the pitch of the framebuffer and the color
format's bits-per-pixel are compatible. omapdss requires that the stride
of a buffer is an integer number of pixels

For example, when using modetest with a display that has x resolution of
1280, and using packed 24 RGB mode (3 bytes per pixel), modetest
allocates a buffer with a byte stride of 4 * 1280 = 5120. But 5120 / 3 =
1706.666... pixels, which causes wrong colors and a tilt on the screen.

Add a check into omapdrm to return an error if the user tries to use
such a combination.

Note: this is not a HW requirement at least for non-rotation use cases,
but a SW driver requirement. In the future we should study if also
rotation use cases are fine with any stride size, and if so, change the
driver to allow these strides.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

drivers/gpu/drm/omapdrm/omap_fb.c

@@ -423,6 +423,14 @@ struct drm_framebuffer *omap_framebuffer_init(struct drm_device *dev,
 			goto fail;
 		}
 
+		if (pitch % format->planes[i].stride_bpp != 0) {
+			dev_err(dev->dev,
+				"buffer pitch (%d bytes) is not a multiple of pixel size (%d bytes)\n",
+				pitch, format->planes[i].stride_bpp);
+			ret = -EINVAL;
+			goto fail;
+		}
+
 		size = pitch * mode_cmd->height / format->planes[i].sub_y;
 
 		if (size > (omap_gem_mmap_size(bos[i]) - mode_cmd->offsets[i])) {