drm/amd/display: Start documentation of DC

[Why]
There are a lot of unintuitive parts of the dm-dc interface.
It would help us if these were documented to provide
a common understanding of what they are supposed to do

[How]
Most of this documentation is stubs, to be filled out more
thoroughly by the experts

Not every dm-accessible function and struct is mentioned.
Simple functions like getters, setters, retain, release,
create, destroy can be left unadorned.

Signed-off-by: David Francis <David.Francis@amd.com>
Reviewed-by: Harry Wentland <Harry.Wentland@amd.com>
Acked-by: Leo Li <sunpeng.li@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dc/core/dc.c

@@ -62,6 +62,55 @@
 
 const static char DC_BUILD_ID[] = "production-build";
 
+/**
+ * DOC: Overview
+ *
+ * DC is the OS-agnostic component of the amdgpu DC driver.
+ *
+ * DC maintains and validates a set of structs representing the state of the
+ * driver and writes that state to AMD hardware
+ *
+ * Main DC HW structs:
+ *
+ * struct dc - The central struct.  One per driver.  Created on driver load,
+ * destroyed on driver unload.
+ *
+ * struct dc_context - One per driver.
+ * Used as a backpointer by most other structs in dc.
+ *
+ * struct dc_link - One per connector (the physical DP, HDMI, miniDP, or eDP
+ * plugpoints).  Created on driver load, destroyed on driver unload.
+ *
+ * struct dc_sink - One per display.  Created on boot or hotplug.
+ * Destroyed on shutdown or hotunplug.  A dc_link can have a local sink
+ * (the display directly attached).  It may also have one or more remote
+ * sinks (in the Multi-Stream Transport case)
+ *
+ * struct resource_pool - One per driver.  Represents the hw blocks not in the
+ * main pipeline.  Not directly accessible by dm.
+ *
+ * Main dc state structs:
+ *
+ * These structs can be created and destroyed as needed.  There is a full set of
+ * these structs in dc->current_state representing the currently programmed state.
+ *
+ * struct dc_state - The global DC state to track global state information,
+ * such as bandwidth values.
+ *
+ * struct dc_stream_state - Represents the hw configuration for the pipeline from
+ * a framebuffer to a display.  Maps one-to-one with dc_sink.
+ *
+ * struct dc_plane_state - Represents a framebuffer.  Each stream has at least one,
+ * and may have more in the Multi-Plane Overlay case.
+ *
+ * struct resource_context - Represents the programmable state of everything in
+ * the resource_pool.  Not directly accessible by dm.
+ *
+ * struct pipe_ctx - A member of struct resource_context.  Represents the
+ * internal hardware pipeline components.  Each dc_plane_state has either
+ * one or two (in the pipe-split case).
+ */
+
 /*******************************************************************************
  * Private functions
  ******************************************************************************/
@@ -240,7 +289,7 @@ bool dc_stream_get_crtc_position(struct dc *dc,
 }
 
 /**
- * dc_stream_configure_crc: Configure CRC capture for the given stream.
+ * dc_stream_configure_crc() - Configure CRC capture for the given stream.
  * @dc: DC Object
  * @stream: The stream to configure CRC on.
  * @enable: Enable CRC if true, disable otherwise.
@@ -292,7 +341,7 @@ bool dc_stream_configure_crc(struct dc *dc, struct dc_stream_state *stream,
 }
 
 /**
- * dc_stream_get_crc: Get CRC values for the given stream.
+ * dc_stream_get_crc() - Get CRC values for the given stream.
  * @dc: DC object
  * @stream: The DC stream state of the stream to get CRCs from.
  * @r_cr, g_y, b_cb: CRC values for the three channels are stored here.
@@ -1329,6 +1378,11 @@ static enum surface_update_type check_update_surfaces_for_stream(
 	return overall_type;
 }
 
+/**
+ * dc_check_update_surfaces_for_stream() - Determine update type (fast, med, or full)
+ *
+ * See :c:type:`enum surface_update_type <surface_update_type>` for explanation of update types
+ */
 enum surface_update_type dc_check_update_surfaces_for_stream(
 		struct dc *dc,
 		struct dc_surface_update *updates,
@@ -1631,6 +1685,9 @@ enum dc_irq_source dc_interrupt_to_irq_source(
 	return dal_irq_service_to_irq_source(dc->res_pool->irqs, src_id, ext_id);
 }
 
+/**
+ * dc_interrupt_set() - Enable/disable an AMD hw interrupt source
+ */
 bool dc_interrupt_set(struct dc *dc, enum dc_irq_source src, bool enable)
 {
 
@@ -1724,6 +1781,11 @@ static bool link_add_remote_sink_helper(struct dc_link *dc_link, struct dc_sink
 	return true;
 }
 
+/**
+ * dc_link_add_remote_sink() - Create a sink and attach it to an existing link
+ *
+ * EDID length is in bytes
+ */
 struct dc_sink *dc_link_add_remote_sink(
 		struct dc_link *link,
 		const uint8_t *edid,
@@ -1782,6 +1844,12 @@ fail_add_sink:
 	return NULL;
 }
 
+/**
+ * dc_link_remove_remote_sink() - Remove a remote sink from a dc_link
+ *
+ * Note that this just removes the struct dc_sink - it doesn't
+ * program hardware or alter other members of dc_link
+ */
 void dc_link_remove_remote_sink(struct dc_link *link, struct dc_sink *sink)
 {
 	int i;

drivers/gpu/drm/amd/display/dc/core/dc_link.c

@@ -198,6 +198,13 @@ static bool program_hpd_filter(
 	return result;
 }
 
+/**
+ * dc_link_detect_sink() - Determine if there is a sink connected
+ *
+ * @type: Returned connection type
+ * Does not detect downstream devices, such as MST sinks
+ * or display connected through active dongles
+ */
 bool dc_link_detect_sink(struct dc_link *link, enum dc_connection_type *type)
 {
 	uint32_t is_hpd_high = 0;
@@ -324,9 +331,9 @@ static enum signal_type get_basic_signal_type(
 	return SIGNAL_TYPE_NONE;
 }
 
-/*
- * @brief
- * Check whether there is a dongle on DP connector
+/**
+ * dc_link_is_dp_sink_present() - Check if there is a native DP
+ * or passive DP-HDMI dongle connected
  */
 bool dc_link_is_dp_sink_present(struct dc_link *link)
 {
@@ -593,6 +600,14 @@ static bool is_same_edid(struct dc_edid *old_edid, struct dc_edid *new_edid)
 	return (memcmp(old_edid->raw_edid, new_edid->raw_edid, new_edid->length) == 0);
 }
 
+/**
+ * dc_link_detect() - Detect if a sink is attached to a given link
+ *
+ * link->local_sink is created or destroyed as needed.
+ *
+ * This does not create remote sinks but will trigger DM
+ * to start MST detection if a branch is detected.
+ */
 bool dc_link_detect(struct dc_link *link, enum dc_detect_reason reason)
 {
 	struct dc_sink_init_data sink_init_data = { 0 };

drivers/gpu/drm/amd/display/dc/core/dc_resource.c

@@ -1447,6 +1447,14 @@ static bool are_stream_backends_same(
 	return true;
 }
 
+/**
+ * dc_is_stream_unchanged() - Compare two stream states for equivalence.
+ *
+ * Checks if there a difference between the two states
+ * that would require a mode change.
+ *
+ * Does not compare cursor position or attributes.
+ */
 bool dc_is_stream_unchanged(
 	struct dc_stream_state *old_stream, struct dc_stream_state *stream)
 {
@@ -1457,6 +1465,9 @@ bool dc_is_stream_unchanged(
 	return true;
 }
 
+/**
+ * dc_is_stream_scaling_unchanged() - Compare scaling rectangles of two streams.
+ */
 bool dc_is_stream_scaling_unchanged(
 	struct dc_stream_state *old_stream, struct dc_stream_state *stream)
 {
@@ -1616,6 +1627,9 @@ bool resource_is_stream_unchanged(
 	return false;
 }
 
+/**
+ * dc_add_stream_to_ctx() - Add a new dc_stream_state to a dc_state.
+ */
 enum dc_status dc_add_stream_to_ctx(
 		struct dc *dc,
 		struct dc_state *new_ctx,
@@ -1640,6 +1654,9 @@ enum dc_status dc_add_stream_to_ctx(
 	return res;
 }
 
+/**
+ * dc_remove_stream_from_ctx() - Remove a stream from a dc_state.
+ */
 enum dc_status dc_remove_stream_from_ctx(
 			struct dc *dc,
 			struct dc_state *new_ctx,
@@ -1860,6 +1877,12 @@ enum dc_status resource_map_pool_resources(
 	return DC_ERROR_UNEXPECTED;
 }
 
+/**
+ * dc_resource_state_copy_construct_current() - Creates a new dc_state from existing state
+ * Is a shallow copy.  Increments refcounts on existing streams and planes.
+ * @dc: copy out of dc->current_state
+ * @dst_ctx: copy into this
+ */
 void dc_resource_state_copy_construct_current(
 		const struct dc *dc,
 		struct dc_state *dst_ctx)
@@ -1875,6 +1898,14 @@ void dc_resource_state_construct(
 	dst_ctx->dccg = dc->res_pool->clk_mgr;
 }
 
+/**
+ * dc_validate_global_state() - Determine if HW can support a given state
+ * Checks HW resource availability and bandwidth requirement.
+ * @dc: dc struct for this driver
+ * @new_ctx: state to be validated
+ *
+ * Return: DC_OK if the result can be programmed.  Otherwise, an error code.
+ */
 enum dc_status dc_validate_global_state(
 		struct dc *dc,
 		struct dc_state *new_ctx)
@@ -2364,10 +2395,6 @@ void dc_resource_state_destruct(struct dc_state *context)
 	}
 }
 
-/*
- * Copy src_ctx into dst_ctx and retain all surfaces and streams referenced
- * by the src_ctx
- */
 void dc_resource_state_copy_construct(
 		const struct dc_state *src_ctx,
 		struct dc_state *dst_ctx)

drivers/gpu/drm/amd/display/dc/core/dc_stream.c

@@ -170,7 +170,7 @@ struct dc_stream_status *dc_stream_get_status(
 }
 
 /**
- * Update the cursor attributes and set cursor surface address
+ * dc_stream_set_cursor_attributes() - Update cursor attributes and set cursor surface address
  */
 bool dc_stream_set_cursor_attributes(
 	struct dc_stream_state *stream,

drivers/gpu/drm/amd/display/dc/dc_link.h

@@ -128,8 +128,10 @@ struct dc_link {
 
 const struct dc_link_status *dc_link_get_status(const struct dc_link *dc_link);
 
-/*
- * Return an enumerated dc_link.  dc_link order is constant and determined at
+/**
+ * dc_get_link_at_index() - Return an enumerated dc_link.
+ *
+ * dc_link order is constant and determined at
  * boot time.  They cannot be created or destroyed.
  * Use dc_get_caps() to get number of links.
  */

drivers/gpu/drm/amd/display/dc/inc/core_types.h

@@ -272,6 +272,17 @@ union bw_context {
 	struct dce_bw_output dce;
 };
 
+/**
+ * struct dc_state - The full description of a state requested by a user
+ *
+ * @streams: Stream properties
+ * @stream_status: The planes on a given stream
+ * @res_ctx: Persistent state of resources
+ * @bw: The output from bandwidth and watermark calculations
+ * @pp_display_cfg: PowerPlay clocks and settings
+ * @dcn_bw_vars: non-stack memory to support bandwidth calculations
+ *
+ */
 struct dc_state {
 	struct dc_stream_state *streams[MAX_PIPES];
 	struct dc_stream_status stream_status[MAX_PIPES];
@@ -279,7 +290,6 @@ struct dc_state {
 
 	struct resource_context res_ctx;
 
-	/* The output from BW and WM calculations. */
 	union bw_context bw;
 
 	/* Note: these are big structures, do *not* put on stack! */