drm/i915/dsb: Documentation for DSB.

Added docbook info regarding Display State Buffer(DSB) which
is added from gen12 onwards to batch submit display HW programming.

v1: Initial version as RFC.

Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Shashank Sharma <shashank.sharma@intel.com>
Reviewed-by: Shashank Sharma <shashank.sharma@intel.com>
Signed-off-by: Animesh Manna <animesh.manna@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190920115930.27829-11-animesh.manna@intel.com

Documentation/gpu/i915.rst

@@ -246,6 +246,15 @@ Display PLLs
 .. kernel-doc:: drivers/gpu/drm/i915/display/intel_dpll_mgr.h
    :internal:
 
+Display State Buffer
+--------------------
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_dsb.c
+   :doc: DSB
+
+.. kernel-doc:: drivers/gpu/drm/i915/display/intel_dsb.c
+   :internal:
+
 Memory Management and Command Submission
 ========================================
 

drivers/gpu/drm/i915/display/intel_dsb.c

@@ -9,6 +9,23 @@
 
 #define DSB_BUF_SIZE    (2 * PAGE_SIZE)
 
+/**
+ * DOC: DSB
+ *
+ * A DSB (Display State Buffer) is a queue of MMIO instructions in the memory
+ * which can be offloaded to DSB HW in Display Controller. DSB HW is a DMA
+ * engine that can be programmed to download the DSB from memory.
+ * It allows driver to batch submit display HW programming. This helps to
+ * reduce loading time and CPU activity, thereby making the context switch
+ * faster. DSB Support added from Gen12 Intel graphics based platform.
+ *
+ * DSB's can access only the pipe, plane, and transcoder Data Island Packet
+ * registers.
+ *
+ * DSB HW can support only register writes (both indexed and direct MMIO
+ * writes). There are no registers reads possible with DSB HW engine.
+ */
+
 /* DSB opcodes. */
 #define DSB_OPCODE_SHIFT		24
 #define DSB_OPCODE_MMIO_WRITE		0x1
@@ -66,6 +83,17 @@ static inline bool intel_dsb_disable_engine(struct intel_dsb *dsb)
 	return true;
 }
 
+/**
+ * intel_dsb_get() - Allocate DSB context and return a DSB instance.
+ * @crtc: intel_crtc structure to get pipe info.
+ *
+ * This function provides handle of a DSB instance, for the further DSB
+ * operations.
+ *
+ * Returns: address of Intel_dsb instance requested for.
+ * Failure: Returns the same DSB instance, but without a command buffer.
+ */
+
 struct intel_dsb *
 intel_dsb_get(struct intel_crtc *crtc)
 {
@@ -116,6 +144,14 @@ intel_dsb_get(struct intel_crtc *crtc)
 	return dsb;
 }
 
+/**
+ * intel_dsb_put() - To destroy DSB context.
+ * @dsb: intel_dsb structure.
+ *
+ * This function destroys the DSB context allocated by a dsb_get(), by
+ * unpinning and releasing the VMA object associated with it.
+ */
+
 void intel_dsb_put(struct intel_dsb *dsb)
 {
 	struct intel_crtc *crtc = container_of(dsb, typeof(*crtc), dsb);
@@ -138,6 +174,19 @@ void intel_dsb_put(struct intel_dsb *dsb)
 	}
 }
 
+/**
+ * intel_dsb_indexed_reg_write() -Write to the DSB context for auto
+ * increment register.
+ * @dsb: intel_dsb structure.
+ * @reg: register address.
+ * @val: value.
+ *
+ * This function is used for writing register-value pair in command
+ * buffer of DSB for auto-increment register. During command buffer overflow,
+ * a warning is thrown and rest all erroneous condition register programming
+ * is done through mmio write.
+ */
+
 void intel_dsb_indexed_reg_write(struct intel_dsb *dsb, i915_reg_t reg,
 				 u32 val)
 {
@@ -202,6 +251,18 @@ void intel_dsb_indexed_reg_write(struct intel_dsb *dsb, i915_reg_t reg,
 		buf[dsb->free_pos] = 0;
 }
 
+/**
+ * intel_dsb_reg_write() -Write to the DSB context for normal
+ * register.
+ * @dsb: intel_dsb structure.
+ * @reg: register address.
+ * @val: value.
+ *
+ * This function is used for writing register-value pair in command
+ * buffer of DSB. During command buffer overflow, a warning  is thrown
+ * and rest all erroneous condition register programming is done
+ * through mmio write.
+ */
 void intel_dsb_reg_write(struct intel_dsb *dsb, i915_reg_t reg, u32 val)
 {
 	struct intel_crtc *crtc = container_of(dsb, typeof(*crtc), dsb);
@@ -225,6 +286,13 @@ void intel_dsb_reg_write(struct intel_dsb *dsb, i915_reg_t reg, u32 val)
 			       i915_mmio_reg_offset(reg);
 }
 
+/**
+ * intel_dsb_commit() - Trigger workload execution of DSB.
+ * @dsb: intel_dsb structure.
+ *
+ * This function is used to do actual write to hardware using DSB.
+ * On errors, fall back to MMIO. Also this function help to reset the context.
+ */
 void intel_dsb_commit(struct intel_dsb *dsb)
 {
 	struct intel_crtc *crtc = container_of(dsb, typeof(*crtc), dsb);