drm/vram: Add helpers to validate a display mode's memory requirements

Devices with low amount of dedicated video memory may not be able
to use all possible display modes, as the framebuffers may not fit
into VRAM. The new helper function drm_vram_helper_mode_valid()
implements a simple test to sort out all display modes that can
not be used in any case. Drivers should call this function from
struct drm_mode_config_funcs.mode_valid.

The functionality was originally implemented by the ast driver, which
is being converted as well.

v2:
	* WARN_ON if VRAM memory manager has not been initialized
	* documentation fixes
	* unexported drm_vram_helper_mode_valid_internal()

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20200203155258.9346-2-tzimmermann@suse.de

1 files changed, 1 insertions, 23 deletions

diff --git a/drivers/gpu/drm/ast/ast_main.c b/drivers/gpu/drm/ast/ast_main.c
index b79f484e9bd2..18a0a4ce00f6 100644
--- a/drivers/gpu/drm/ast/ast_main.c
+++ b/drivers/gpu/drm/ast/ast_main.c
@@ -388,31 +388,9 @@ static int ast_get_dram_info(struct drm_device *dev)
 	return 0;
 }
 
-enum drm_mode_status ast_mode_config_mode_valid(struct drm_device *dev,
-						const struct drm_display_mode *mode)
-{
-	static const unsigned long max_bpp = 4; /* DRM_FORMAT_XRGBA8888 */
-
-	struct ast_private *ast = dev->dev_private;
-	unsigned long fbsize, fbpages, max_fbpages;
-
-	/* To support double buffering, a framebuffer may not
-	 * consume more than half of the available VRAM.
-	 */
-	max_fbpages = (ast->vram_size / 2) >> PAGE_SHIFT;
-
-	fbsize = mode->hdisplay * mode->vdisplay * max_bpp;
-	fbpages = DIV_ROUND_UP(fbsize, PAGE_SIZE);
-
-	if (fbpages > max_fbpages)
-		return MODE_MEM;
-
-	return MODE_OK;
-}
-
 static const struct drm_mode_config_funcs ast_mode_funcs = {
 	.fb_create = drm_gem_fb_create,
-	.mode_valid = ast_mode_config_mode_valid,
+	.mode_valid = drm_vram_helper_mode_valid,
 	.atomic_check = drm_atomic_helper_check,
 	.atomic_commit = drm_atomic_helper_commit,
 };