drm/amd/display: Expand documentation for timing

The timing programming inside DCN is far from trivial, it has multiple
parameters associated with that, and the lack of documentation does not
help comprehend this already complicated topic. This commit tries to
improve this situation by expanding the documentation of dc_crtc_timing
and the VTG program function.

Reviewed-by: Harry Wentland <[e-mail]>
Acked-by: Tom Chung <[e-mail]>
Signed-off-by: Rodrigo Siqueira <[e-mail]>
Tested-by: Daniel Wheeler <[e-mail]>
Signed-off-by: Alex Deucher <[e-mail]>

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

···
 	bool is_dp; /* indicate if DSC is applied based on DP's capability */
 	uint32_t mst_pbn; /* pbn of display on dsc mst hub */
 };
+
+/**
+ * struct dc_crtc_timing - Timing parameters used to configure DCN blocks
+ *
+ * DCN provides multiple signals and parameters that can be used to adjust
+ * timing parameters, this struct aggregate multiple of these values for easy
+ * access. In this struct, fields prefixed with h_* are related to horizontal
+ * timing, and v_* to vertical timing. Keep in mind that when we talk about
+ * vertical timings, the values, in general, are described in the number of
+ * lines; on the other hand, the horizontal values are in pixels.
+ */
 struct dc_crtc_timing {
+	/**
+	 * @h_total: The total number of pixels from the rising edge of HSync
+	 * until the rising edge of the current HSync.
+	 */
 	uint32_t h_total;
+
+	/**
+	 * @h_border_left: The black pixels related to the left border
+	 */
 	uint32_t h_border_left;
+
+	/**
+	 * @h_addressable: It is the range of pixels displayed horizontally.
+	 * For example, if the display resolution is 3840@2160, the horizontal
+	 * addressable area is 3840.
+	 */
 	uint32_t h_addressable;
+
+	/**
+	 * @h_border_right: The black pixels related to the right border
+	 */
 	uint32_t h_border_right;
+
+	/**
+	 * @h_front_porch: Period (in pixels) between HBlank start and the
+	 * rising edge of HSync.
+	 */
 	uint32_t h_front_porch;
+
+	/**
+	 * @h_sync_width: HSync duration in pixels.
+	 */
 	uint32_t h_sync_width;
 
+	/**
+	 * @v_total: It is the total number of lines from the rising edge of
+	 * the previous VSync until the rising edge of the current VSync.
+	 *
+	 *          |--------------------------|
+	 *          +-+        V_TOTAL         +-+
+	 *          | |                        | |
+	 * VSync ---+ +--------- // -----------+ +---
+	 */
 	uint32_t v_total;
+
+	/**
+	 * @v_border_top: The black border on the top.
+	 */
 	uint32_t v_border_top;
+
+	/**
+	 * @v_addressable: It is the range of the scanout at which the
+	 * framebuffer is displayed. For example, if the display resolution is
+	 * 3840@2160, the addressable area is 2160 lines, or if the resolution
+	 * is 1920x1080, the addressable area is 1080 lines.
+	 */
 	uint32_t v_addressable;
+
+	/**
+	 * @v_border_bottom: The black border on the bottom.
+	 */
 	uint32_t v_border_bottom;
+
+	/**
+	 * @v_front_porch: Period (in lines) between VBlank start and rising
+	 * edge of VSync.
+	 *                  +-+
+	 * VSync            | |
+	 *        ----------+ +--------...
+	 *          +------------------...
+	 * VBlank   |
+	 *        --+
+	 *          |-------|
+	 *        v_front_porch
+	 */
 	uint32_t v_front_porch;
+
+	/**
+	 * @v_sync_width: VSync signal width in lines.
+	 */
 	uint32_t v_sync_width;
 
+	/**
+	 * @pix_clk_100hz: Pipe pixel precision
+	 *
+	 * This field is used to communicate pixel clocks with 100 Hz accuracy
+	 * from dc_crtc_timing to BIOS command table.
+	 */
 	uint32_t pix_clk_100hz;
+
 	uint32_t min_refresh_in_uhz;
 
 	uint32_t vic;

drivers/gpu/drm/amd/display/dc/dcn10/dcn10_optc.c

···
 	}
 }
 
+/**
+ * optc1_set_vtg_params - Set Vertical Timing Generator (VTG) parameters
+ *
+ * @optc: timing_generator struct used to extract the optc parameters
+ * @dc_crtc_timing: Timing parameters configured
+ * @program_fp2: Boolean value indicating if FP2 will be programmed or not
+ *
+ * OTG is responsible for generating the global sync signals, including
+ * vertical timing information for each HUBP in the dcfclk domain. Each VTG is
+ * associated with one OTG that provides HUBP with vertical timing information
+ * (i.e., there is 1:1 correspondence between OTG and VTG). This function is
+ * responsible for setting the OTG parameters to the VTG during the pipe
+ * programming.
+ */
 void optc1_set_vtg_params(struct timing_generator *optc,
 		const struct dc_crtc_timing *dc_crtc_timing, bool program_fp2)
 {