1/* SPDX-License-Identifier: GPL-2.0+ */
2/*
3 * (C) 2015 Siarhei Siamashka <siarhei.siamashka@gmail.com>
4 */
5
6/*
7 * Support for the SSD2828 bridge chip, which can take pixel data coming
8 * from a parallel LCD interface and translate it on the flight into MIPI DSI
9 * interface for driving a MIPI compatible TFT display.
10 *
11 * Implemented as a utility function. To be used from display drivers, which are
12 * responsible for driving parallel LCD hardware in front of the video pipeline.
13 */
14
15#ifndef _SSD2828_H
16#define _SSD2828_H
17
18struct ctfb_res_modes;
19
20struct ssd2828_config {
21	/*********************************************************************/
22	/* SSD2828 configuration                                             */
23	/*********************************************************************/
24
25	/*
26	 * The pins, which are used for SPI communication. This is only used
27	 * for configuring SSD2828, so the performance is irrelevant (only
28	 * around a hundred of bytes is moved). Also these can be any arbitrary
29	 * GPIO pins (not necessarily the pins having hardware SPI function).
30	 * Moreover, the 'sdo' pin may be even not wired up in some devices.
31	 *
32	 * These configuration variables need to be set as pin numbers for
33	 * the standard u-boot GPIO interface (gpio_get_value/gpio_set_value
34	 * functions). Note that -1 value can be used for the pins, which are
35	 * not really wired up.
36	 */
37	int csx_pin;
38	int sck_pin;
39	int sdi_pin;
40	int sdo_pin;
41	/* SSD2828 reset pin (shared with LCD panel reset) */
42	int reset_pin;
43
44	/*
45	 * The SSD2828 has its own dedicated clock source 'tx_clk' (connected
46	 * to TX_CLK_XIO/TX_CLK_XIN pins), which is necessary at least for
47	 * clocking SPI after reset. The exact clock speed is not strictly,
48	 * defined, but the datasheet says that it must be somewhere in the
49	 * 8MHz - 30MHz range (see "TX_CLK Timing" section). It can be also
50	 * used as a reference clock for PLL. If the exact clock frequency
51	 * is known, then it can be specified here. If it is unknown, or the
52	 * information is not trustworthy, then it can be set to 0.
53	 *
54	 * If unsure, set to 0.
55	 */
56	int ssd2828_tx_clk_khz;
57
58	/*
59	 * This is not a property of the used LCD panel, but more like a
60	 * property of the SSD2828 wiring. See the "SSD2828QN4 RGB data
61	 * arrangement" table in the datasheet. The SSD2828 pins are arranged
62	 * in such a way that 18bpp and 24bpp configurations are completely
63	 * incompatible with each other.
64	 *
65	 * Depending on the color depth, this must be set to 16, 18 or 24.
66	 */
67	int ssd2828_color_depth;
68
69	/*********************************************************************/
70	/* LCD panel configuration                                           */
71	/*********************************************************************/
72
73	/*
74	 * The number of lanes in the MIPI DSI interface. May vary from 1 to 4.
75	 *
76	 * This information can be found in the LCD panel datasheet.
77	 */
78	int mipi_dsi_number_of_data_lanes;
79
80	/*
81	 * Data transfer bit rate per lane. Please note that it is expected
82	 * to be higher than the pixel clock rate of the used video mode when
83	 * multiplied by the number of lanes. This is perfectly normal because
84	 * MIPI DSI handles data transfers in periodic bursts, and uses the
85	 * idle time between bursts for sending configuration information and
86	 * commands. Or just for saving power.
87	 *
88	 * The necessary Mbps/lane information can be found in the LCD panel
89	 * datasheet. Note that the transfer rate can't be always set precisely
90	 * and it may be rounded *up* (introducing no more than 10Mbps error).
91	 */
92	int mipi_dsi_bitrate_per_data_lane_mbps;
93
94	/*
95	 * Setting this to 1 enforces packing of 18bpp pixel data in 24bpp
96	 * envelope when sending it over the MIPI DSI link.
97	 *
98	 * If unsure, set to 0.
99	 */
100	int mipi_dsi_loosely_packed_pixel_format;
101
102	/*
103	 * According to the "Example for system sleep in and out" section in
104	 * the SSD2828 datasheet, some LCD panel specific delays are necessary
105	 * after MIPI DCS commands EXIT_SLEEP_MODE and SET_DISPLAY_ON.
106	 *
107	 * For example, Allwinner uses 100 milliseconds delay after
108	 * EXIT_SLEEP_MODE and 200 milliseconds delay after SET_DISPLAY_ON.
109	 */
110	int mipi_dsi_delay_after_exit_sleep_mode_ms;
111	int mipi_dsi_delay_after_set_display_on_ms;
112};
113
114/*
115 * Initialize the SSD2828 chip. It needs the 'ssd2828_config' structure
116 * and also the video mode timings.
117 *
118 * The right place to insert this function call is after the parallel LCD
119 * interface is initialized and before turning on the backlight. This is
120 * advised in the "Example for system sleep in and out" section of the
121 * SSD2828 datasheet. And also SS2828 may use 'pclk' as the clock source
122 * for PLL, which means that the input signal must be already there.
123 */
124int ssd2828_init(const struct ssd2828_config *cfg,
125		 const struct ctfb_res_modes *mode);
126
127#endif
128