drm: simple_kms_helper: Fix .mode_valid() documentation

This fixes up the .mode_valid() vtable entry documentation
by copyediting the documentation from the .mode_valid()
documentation in the drm_modeset_helper_vtables.h file.

Fixes: 40275dc4edb4 ("drm: simple_kms_helper: Add mode_valid() callback support")
Suggested-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20180227101109.6088-1-linus.walleij@linaro.org

diff --git a/include/drm/drm_simple_kms_helper.h b/include/drm/drm_simple_kms_helper.h
index c4e32c5..1b4e352 100644 (file)
--- a/include/drm/drm_simple_kms_helper.h
+++ b/include/drm/drm_simple_kms_helper.h
@@ -24,9 +24,30 @@ struct drm_simple_display_pipe_funcs {
        /**
         * @mode_valid:
         *
-        * This function is called to filter out valid modes from the
-        * suggestions suggested by the bridge or display. This optional
-        * hook is passed in when initializing the pipeline.
+        * This callback is used to check if a specific mode is valid in the
+        * crtc used in this simple display pipe. This should be implemented
+        * if the display pipe has some sort of restriction in the modes
+        * it can display. For example, a given display pipe may be responsible
+        * to set a clock value. If the clock can not produce all the values
+        * for the available modes then this callback can be used to restrict
+        * the number of modes to only the ones that can be displayed. Another
+        * reason can be bandwidth mitigation: the memory port on the display
+        * controller can have bandwidth limitations not allowing pixel data
+        * to be fetched at any rate.
+        *
+        * This hook is used by the probe helpers to filter the mode list in
+        * drm_helper_probe_single_connector_modes(), and it is used by the
+        * atomic helpers to validate modes supplied by userspace in
+        * drm_atomic_helper_check_modeset().
+        *
+        * This function is optional.
+        *
+        * NOTE:
+        *
+        * Since this function is both called from the check phase of an atomic
+        * commit, and the mode validation in the probe paths it is not allowed
+        * to look at anything else but the passed-in mode, and validate it
+        * against configuration-invariant hardware constraints.
         *
         * RETURNS:
         *