drm: Docbook integration and over sections for all the new helpers

In all cases the text requires that new drivers are converted to the
atomic interfaces.

v2: Add overview for state handling.

v3: Review from Sean: Some spelling fixes and drop the misguided
hunk to remove rgba8888 from the plane helpers compat list.

Cc: Sean Paul <seanpaul@chromium.org>
Reviewed-by: Sean Paul <seanpaul@chromium.org>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

3 files changed, 82 insertions, 0 deletions

diff --git a/drivers/gpu/drm/drm_atomic_helper.c b/drivers/gpu/drm/drm_atomic_helper.c
index 2c38bda217ec..2b1db0c12fdc 100644
--- a/drivers/gpu/drm/drm_atomic_helper.c
+++ b/drivers/gpu/drm/drm_atomic_helper.c
@@ -32,6 +32,27 @@
 #include <drm/drm_atomic_helper.h>
 #include <linux/fence.h>
 
+/**
+ * DOC: overview
+ *
+ * This helper library provides implementations of check and commit functions on
+ * top of the CRTC modeset helper callbacks and the plane helper callbacks. It
+ * also provides convenience implementations for the atomic state handling
+ * callbacks for drivers which don't need to subclass the drm core structures to
+ * add their own additional internal state.
+ *
+ * This library also provides default implementations for the check callback in
+ * drm_atomic_helper_check and for the commit callback with
+ * drm_atomic_helper_commit. But the individual stages and callbacks are expose
+ * to allow drivers to mix and match and e.g. use the plane helpers only
+ * together with a driver private modeset implementation.
+ *
+ * This library also provides implementations for all the legacy driver
+ * interfaces on top of the atomic interface. See drm_atomic_helper_set_config,
+ * drm_atomic_helper_disable_plane, drm_atomic_helper_disable_plane and the
+ * various functions to implement set_property callbacks. New drivers must not
+ * implement these functions themselves but must use the provided helpers.
+ */
 static void
 drm_atomic_helper_plane_changed(struct drm_atomic_state *state,
 				struct drm_plane_state *plane_state,
@@ -1708,6 +1729,21 @@ backoff:
 EXPORT_SYMBOL(drm_atomic_helper_page_flip);
 
 /**
+ * DOC: atomic state reset and initialization
+ *
+ * Both the drm core and the atomic helpers assume that there is always the full
+ * and correct atomic software state for all connectors, CRTCs and planes
+ * available. Which is a bit a problem on driver load and also after system
+ * suspend. One way to solve this is to have a hardware state read-out
+ * infrastructure which reconstructs the full software state (e.g. the i915
+ * driver).
+ *
+ * The simpler solution is to just reset the software state to everything off,
+ * which is easiest to do by calling drm_mode_config_reset(). To facilitate this
+ * the atomic helpers provide default reset implementations for all hooks.
+ */
+
+/**
  * drm_atomic_helper_crtc_reset - default ->reset hook for CRTCs
  * @crtc: drm CRTC
  *
diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
index 46728a8ac622..33195e9adaab 100644
--- a/drivers/gpu/drm/drm_crtc_helper.c
+++ b/drivers/gpu/drm/drm_crtc_helper.c
@@ -41,6 +41,26 @@
 #include <drm/drm_plane_helper.h>
 #include <drm/drm_edid.h>
 
+/**
+ * DOC: overview
+ *
+ * The CRTC modeset helper library provides a default set_config implementation
+ * in drm_crtc_helper_set_config(). Plus a few other convenience functions using
+ * the same callbacks which drivers can use to e.g. restore the modeset
+ * configuration on resume with drm_helper_resume_force_mode().
+ *
+ * The driver callbacks are mostly compatible with the atomic modeset helpers,
+ * except for the handling of the primary plane: Atomic helpers require that the
+ * primary plane is implemented as a real standalone plane and not directly tied
+ * to the CRTC state. For easier transition this library provides functions to
+ * implement the old semantics required by the CRTC helpers using the new plane
+ * and atomic helper callbacks.
+ *
+ * Drivers are strongly urged to convert to the atomic helpers (by way of first
+ * converting to the plane helpers). New drivers must not use these functions
+ * but need to implement the atomic interface instead, potentially using the
+ * atomic helpers for that.
+ */
 MODULE_AUTHOR("David Airlie, Jesse Barnes");
 MODULE_DESCRIPTION("DRM KMS helper");
 MODULE_LICENSE("GPL and additional rights");
diff --git a/drivers/gpu/drm/drm_plane_helper.c b/drivers/gpu/drm/drm_plane_helper.c
index a5a295872fbb..fa56bb5da6c3 100644
--- a/drivers/gpu/drm/drm_plane_helper.c
+++ b/drivers/gpu/drm/drm_plane_helper.c
@@ -31,6 +31,32 @@
 
 #define SUBPIXEL_MASK 0xffff
 
+/**
+ * DOC: overview
+ *
+ * This helper library has two parts. The first part has support to implement
+ * primary plane support on top of the normal CRTC configuration interface.
+ * Since the legacy ->set_config interface ties the primary plane together with
+ * the CRTC state this does not allow userspace to disable the primary plane
+ * itself.  To avoid too much duplicated code use
+ * drm_plane_helper_check_update() which can be used to enforce the same
+ * restrictions as primary planes had thus. The default primary plane only
+ * expose XRBG8888 and ARGB8888 as valid pixel formats for the attached
+ * framebuffer.
+ *
+ * Drivers are highly recommended to implement proper support for primary
+ * planes, and newly merged drivers must not rely upon these transitional
+ * helpers.
+ *
+ * The second part also implements transitional helpers which allow drivers to
+ * gradually switch to the atomic helper infrastructure for plane updates. Once
+ * that switch is complete drivers shouldn't use these any longer, instead using
+ * the proper legacy implementations for update and disable plane hooks provided
+ * by the atomic helpers.
+ *
+ * Again drivers are strongly urged to switch to the new interfaces.
+ */
+
 /*
  * This is the minimal list of formats that seem to be safe for modeset use
  * with all current DRM drivers.  Most hardware can actually support more