[9/9] drm: Clarify semantics of struct drm_mode_config.{min, max}_{width, height}

Commit Message

Thomas Zimmermann Oct. 22, 2021, 1:28 p.m. UTC

Add additional information on the semantics of the size fields in
struct drm_mode_config. Also add a TODO to review all driver for
correct usage of these fields.

Signed-off-by: Thomas Zimmermann <[e-mail]>
---
 Documentation/gpu/todo.rst    | 15 +++++++++++++++
 include/drm/drm_mode_config.h | 13 +++++++++++++
 2 files changed, 28 insertions(+)

Patch

diff --git a/Documentation/gpu/todo.rst b/Documentation/gpu/todo.rst
index 60d1d7ee0719..f4e1d72149f7 100644
--- a/Documentation/gpu/todo.rst
+++ b/Documentation/gpu/todo.rst
@@ -463,6 +463,21 @@  Contact: Thomas Zimmermann <[e-mail]>, Christian König, Daniel Vette
 
 Level: Intermediate
 
+Review all drivers for setting struct drm_mode_config.{max_width,max_height} correctly
+--------------------------------------------------------------------------------------
+
+The values in struct drm_mode_config.{max_width,max_height} describe the
+maximum supported framebuffer size. It's the virtual screen size, but many
+drivers treat it like limitations of the physical resolution.
+
+The maximum width depends on the hardware's maximum scanline pitch. The
+maximum height depends on the amount of addressable video memory. Review all
+drivers to initialize the fields to the correct values.
+
+Contact: Thomas Zimmermann <[e-mail]>
+
+Level: Intermediate
+
 
 Core refactorings
 =================
diff --git a/include/drm/drm_mode_config.h b/include/drm/drm_mode_config.h
index 48b7de80daf5..91ca575a78de 100644
--- a/include/drm/drm_mode_config.h
+++ b/include/drm/drm_mode_config.h
@@ -359,6 +359,19 @@  struct drm_mode_config_funcs {
  * Core mode resource tracking structure.  All CRTC, encoders, and connectors
  * enumerated by the driver are added here, as are global properties.  Some
  * global restrictions are also here, e.g. dimension restrictions.
+ *
+ * Framebuffer sizes refer to the virtual screen that can be displayed by
+ * the CRTC. This can be different from the physical resolution programmed.
+ * The minimum width and height, stored in @min_width and @min_height,
+ * describe the smallest size of the framebuffer. It correlates to the
+ * minimum programmable resolution.
+ * The maximum width, stored in @max_width, is typically limited by the
+ * maximum pitch between two adjacent scanlines. The maximum height, stored
+ * in @max_height, is usually only limited by the amount of addressable video
+ * memory. For hardware that has no real maximum, drivers should pick a
+ * reasonable default.
+ *
+ * See also @DRM_SHADOW_PLANE_MAX_WIDTH and @DRM_SHADOW_PLANE_MAX_HEIGHT.
  */
 struct drm_mode_config {
 	/**