drm/amd/display: Initial documentation for AMDgpu DC

[Why]
Documentation is helpful for the community to understand our code.
This change does some high-level documentation of some DM interfaces
with DRM, and the amdgpu base driver.

[How]
An entry for AMDgpu DC has been added to Documentation/gpu/drivers.rst
TOC. amdgpu-dc.rst is created to pull in inline doc-strings, which:
- Provides an overview for "What is DM?"
- Documents AMDgpu DM lifecyle
- Documents IRQ management
- Documents atomic_check and commit_tail interfaces

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

1 files changed, 102 insertions, 13 deletions

diff --git a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_irq.c b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_irq.c
index a212178f2edc..cd10f77cdeb0 100644
--- a/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_irq.c
+++ b/drivers/gpu/drm/amd/display/amdgpu_dm/amdgpu_dm_irq.c
@@ -32,16 +32,55 @@
 #include "amdgpu_dm.h"
 #include "amdgpu_dm_irq.h"
 
+/**
+ * DOC: overview
+ *
+ * DM provides another layer of IRQ management on top of what the base driver
+ * already provides. This is something that could be cleaned up, and is a
+ * future TODO item.
+ *
+ * The base driver provides IRQ source registration with DRM, handler
+ * registration into the base driver's IRQ table, and a handler callback
+ * amdgpu_irq_handler(), with which DRM calls on interrupts. This generic
+ * handler looks up the IRQ table, and calls the respective
+ * &amdgpu_irq_src_funcs.process hookups.
+ *
+ * What DM provides on top are two IRQ tables specifically for top-half and
+ * bottom-half IRQ handling, with the bottom-half implementing workqueues:
+ *
+ * - &amdgpu_display_manager.irq_handler_list_high_tab
+ * - &amdgpu_display_manager.irq_handler_list_low_tab
+ *
+ * They override the base driver's IRQ table, and the effect can be seen
+ * in the hooks that DM provides for &amdgpu_irq_src_funcs.process. They
+ * are all set to the DM generic handler amdgpu_dm_irq_handler(), which looks up
+ * DM's IRQ tables. However, in order for base driver to recognize this hook, DM
+ * still needs to register the IRQ with the base driver. See
+ * dce110_register_irq_handlers() and dcn10_register_irq_handlers().
+ *
+ * To expose DC's hardware interrupt toggle to the base driver, DM implements
+ * &amdgpu_irq_src_funcs.set hooks. Base driver calls it through
+ * amdgpu_irq_update() to enable or disable the interrupt.
+ */
+
 /******************************************************************************
  * Private declarations.
  *****************************************************************************/
 
+/**
+ * struct amdgpu_dm_irq_handler_data - Data for DM interrupt handlers.
+ *
+ * @list: Linked list entry referencing the next/previous handler
+ * @handler: Handler function
+ * @handler_arg: Argument passed to the handler when triggered
+ * @dm: DM which this handler belongs to
+ * @irq_source: DC interrupt source that this handler is registered for
+ */
 struct amdgpu_dm_irq_handler_data {
 	struct list_head list;
 	interrupt_handler handler;
 	void *handler_arg;
 
-	/* DM which this handler belongs to */
 	struct amdgpu_display_manager *dm;
 	/* DAL irq source which registered for this interrupt. */
 	enum dc_irq_source irq_source;
@@ -68,7 +107,7 @@ static void init_handler_common_data(struct amdgpu_dm_irq_handler_data *hcd,
 }
 
 /**
- * dm_irq_work_func - Handle an IRQ outside of the interrupt handler proper.
+ * dm_irq_work_func() - Handle an IRQ outside of the interrupt handler proper.
  *
  * @work: work struct
  */
@@ -99,8 +138,8 @@ static void dm_irq_work_func(struct work_struct *work)
 	 * (The most common use is HPD interrupt) */
 }
 
-/**
- * Remove a handler and return a pointer to hander list from which the
+/*
+ * Remove a handler and return a pointer to handler list from which the
  * handler was removed.
  */
 static struct list_head *remove_irq_handler(struct amdgpu_device *adev,
@@ -203,6 +242,24 @@ static bool validate_irq_unregistration_params(enum dc_irq_source irq_source,
  * Note: caller is responsible for input validation.
  *****************************************************************************/
 
+/**
+ * amdgpu_dm_irq_register_interrupt() - Register a handler within DM.
+ * @adev: The base driver device containing the DM device.
+ * @int_params: Interrupt parameters containing the source, and handler context
+ * @ih: Function pointer to the interrupt handler to register
+ * @handler_args: Arguments passed to the handler when the interrupt occurs
+ *
+ * Register an interrupt handler for the given IRQ source, under the given
+ * context. The context can either be high or low. High context handlers are
+ * executed directly within ISR context, while low context is executed within a
+ * workqueue, thereby allowing operations that sleep.
+ *
+ * Registered handlers are called in a FIFO manner, i.e. the most recently
+ * registered handler will be called first.
+ *
+ * Return: Handler data &struct amdgpu_dm_irq_handler_data containing the IRQ
+ *         source, handler function, and args
+ */
 void *amdgpu_dm_irq_register_interrupt(struct amdgpu_device *adev,
 				       struct dc_interrupt_params *int_params,
 				       void (*ih)(void *),
@@ -261,6 +318,15 @@ void *amdgpu_dm_irq_register_interrupt(struct amdgpu_device *adev,
 	return handler_data;
 }
 
+/**
+ * amdgpu_dm_irq_unregister_interrupt() - Remove a handler from the DM IRQ table
+ * @adev: The base driver device containing the DM device
+ * @irq_source: IRQ source to remove the given handler from
+ * @ih: Function pointer to the interrupt handler to unregister
+ *
+ * Go through both low and high context IRQ tables, and find the given handler
+ * for the given irq source. If found, remove it. Otherwise, do nothing.
+ */
 void amdgpu_dm_irq_unregister_interrupt(struct amdgpu_device *adev,
 					enum dc_irq_source irq_source,
 					void *ih)
@@ -295,6 +361,20 @@ void amdgpu_dm_irq_unregister_interrupt(struct amdgpu_device *adev,
 	}
 }
 
+/**
+ * amdgpu_dm_irq_init() - Initialize DM IRQ management
+ * @adev:  The base driver device containing the DM device
+ *
+ * Initialize DM's high and low context IRQ tables.
+ *
+ * The N by M table contains N IRQ sources, with M
+ * &struct amdgpu_dm_irq_handler_data hooked together in a linked list. The
+ * list_heads are initialized here. When an interrupt n is triggered, all m
+ * handlers are called in sequence, FIFO according to registration order.
+ *
+ * The low context table requires special steps to initialize, since handlers
+ * will be deferred to a workqueue. See &struct irq_list_head.
+ */
 int amdgpu_dm_irq_init(struct amdgpu_device *adev)
 {
 	int src;
@@ -317,7 +397,12 @@ int amdgpu_dm_irq_init(struct amdgpu_device *adev)
 	return 0;
 }
 
-/* DM IRQ and timer resource release */
+/**
+ * amdgpu_dm_irq_fini() - Tear down DM IRQ management
+ * @adev: The base driver device containing the DM device
+ *
+ * Flush all work within the low context IRQ table.
+ */
 void amdgpu_dm_irq_fini(struct amdgpu_device *adev)
 {
 	int src;
@@ -414,7 +499,7 @@ int amdgpu_dm_irq_resume_late(struct amdgpu_device *adev)
 	return 0;
 }
 
-/**
+/*
  * amdgpu_dm_irq_schedule_work - schedule all work items registered for the
  * "irq_source".
  */
@@ -439,8 +524,9 @@ static void amdgpu_dm_irq_schedule_work(struct amdgpu_device *adev,
 
 }
 
-/** amdgpu_dm_irq_immediate_work
- *  Callback high irq work immediately, don't send to work queue
+/*
+ * amdgpu_dm_irq_immediate_work
+ * Callback high irq work immediately, don't send to work queue
  */
 static void amdgpu_dm_irq_immediate_work(struct amdgpu_device *adev,
 					 enum dc_irq_source irq_source)
@@ -467,11 +553,14 @@ static void amdgpu_dm_irq_immediate_work(struct amdgpu_device *adev,
 	DM_IRQ_TABLE_UNLOCK(adev, irq_table_flags);
 }
 
-/*
- * amdgpu_dm_irq_handler
+/**
+ * amdgpu_dm_irq_handler - Generic DM IRQ handler
+ * @adev: amdgpu base driver device containing the DM device
+ * @source: Unused
+ * @entry: Data about the triggered interrupt
  *
- * Generic IRQ handler, calls all registered high irq work immediately, and
- * schedules work for low irq
+ * Calls all registered high irq work immediately, and schedules work for low
+ * irq. The DM IRQ table is used to find the corresponding handlers.
  */
 static int amdgpu_dm_irq_handler(struct amdgpu_device *adev,
 				 struct amdgpu_irq_src *source,
@@ -613,7 +702,7 @@ void amdgpu_dm_set_irq_funcs(struct amdgpu_device *adev)
 	adev->hpd_irq.funcs = &dm_hpd_irq_funcs;
 }
 
-/*
+/**
  * amdgpu_dm_hpd_init - hpd setup callback.
  *
  * @adev: amdgpu_device pointer