Some descriptions of Mipi protocol of LCD

MIPI：LCD LCD MIPI Interface is Mobile Industry Processor Interface Abbreviation .MIPI（ Mobile industry processor interface ） yes MIPI Open standards for mobile application processors initiated by the Alliance .MIPI It is a relatively new standard , Its specifications are also constantly revised and improved , At present, the more mature interface applications are DSI( Display interface ) and CSI（ Camera interface ）.CSI/DSI Respectively, it means that the bearing is aimed at Camera or Display Show apps , Both have complex protocol structures .

MIPI—DSI It's a kind of Lane Extensible interface ,1 A clock channel /1-4 Two data channels . most 4 Channels , Each channel supports one-way high-speed communication ,0 Low speed two-way communication can be selected for the channel .DSI There are generally two operation modes ：

• Command mode ：Command Mode. Generally, high-speed or low-power transmission mode is ok , Corresponding MCU Interface .
• Video mode ：Video Mode. High speed mode transmission must be used , Corresponding RGB Interface （ but LCD Set to Video Mode when , Usually call Command Mode Read / write operation register , To complete LCD Initialization of modules , Image data uses Video Mode） There are three modes of video transmission ：
  • Burst mode
  • Non-burst Mode Sync event （ Synchronous event mode ）
  • Non-burst Mode Sync pulses（ Synchronous pulse mode ）

DSI The agreement can be divided into 4 layer ： It is mainly divided into four layers ： application layer ( display )、 Protocol layer (dsi agreement )、 Channel management 、 The physical layer （D-PHY）.( host )cpu-> application layer （DDR）-> Protocol layer （DSI）-> Channel management -> The physical layer （DPHY） The physical layer -> Channel management -> Protocol layer -> application layer -> Display module .

MIPI-DSI Belong to MIPI Sub protocol , by Display Specifications and standards for display module interfaces developed by the working group .MIPI-DSI Use D-PHY Transmit as physical layer .D-PHY There are two transmission modes

• LP, Low power transmission mode ( Single signal ). Only applicable to 0 passageway , It is generally used to transmit control commands , At low speed, the data is not easy to make mistakes and easy to measure .10Mbps transmission speed , The voltage is generally 0-1.2V.
• HS： High speed transmission mode ( Differential signal ).4 Both channels can be used , Transmit high-speed image data .80M~1Gbps transmission speed , The voltage is generally 100~300mv, In general use 200mv .

MIPI-DSI Data transfer format ：

Composition of general command transmission types ： Package type 、 Time delay 、 The number of data （ register + value ）、 register 、 value . The composition order of different platform definitions is inconsistent . Such as sprd：0x29, 0x00, 0x00, 0x02, 0x4B, 0x1D. Package type ：0x29、 Time delay 0x00, 0x00、 The number of data 0x02（ register + value ）、 register 0x4B、 value 0x1D

Package type 0x29 and 0x39 Can mean multi parameter ,0x03 and 0x05 Can mean no parameter ,0x13 and 0x15 Can mean single parameter .DSI Agreement ,0x29 and 0x39 difference ： stay Mipi Agreement , Both of them mean Long bag （Long Packet） data type . however Mipi DSI Of Spec The difference between the two is written in 0x29 Belong to Generic long write ,0x39 Belong to DCS long write.

• DCS System read / write commands , With parameters , Commonly used in LCD Initialization parameter command .
• Generic Is a read / write command , It is a command outside the protocol specification , Usually a few IC custom , Just make sure that the host and peripherals agree with these data formats , Usually and DCS Universal .

MIPI host dts Configuration of

## MIPI Host To configure 
disp_mipi_init: mipi_dsi_init{
        compatible = "rockchip,mipi_dsi_init";
        rockchip,screen_init    = <1>; /*  Whether to be in  dtsi  In the initialization  1 0 */
        rockchip,dsi_lane       = <4>; /*  want ⼏ Data  lane , According to the schematic diagram and  mipi  Specifications */
        /* ddr clk ⼀ strip  lane  The transmission rate of  Mbits/s  */
        /* 100 + H_total×V_total×fps×3（⼀ individual rgb by 3 byte ）×8（8bits）/lanes  */
        /*  this ⾥ Of  total  refer to  sync + front + back + active */
        /* ⽐ Such as  H_total = Hsync + HFP(hfront-proch)  + HBP(hback-porch) + Hactive  */
        rockchip,dsi_hs_clk     = <1000>
        rockchip,mipi_dsi_num   = <1>; /*  single mipi  Or double  mipi*/
};

##  Panel power control configuration 
disp_mipi_power_ctr: mipi_power_ctr {
        compatible = "rockchip,mipi_power_ctr";
        mipi_lcd_rst:mipi_lcd_rst{
                compatible = "rockchip,lcd_rst";
                rockchip,gpios = <&gpio2 GPIO_B7 GPIO_ACTIVE_LOW>;
                rockchip,delay = <100>;
        };
        /*
        //  To configure  lcd_en GPIO  which ⼀ road , Maybe not  LCD_EN  So that is  VCC  Constant power supply 
        mipi_lcd_en:mipi_lcd_en {
                compatible = "rockchip,lcd_en";
                rockchip,gpios = <&gpio0 GPIO_C1 GPIO_ACTIVE_HIGH>;
                rockchip,delay = <100>;
        };
        */
        // There may be ⽚ choose  cs
};

##  Screen initialization sequence 
disp_mipi_init_cmds: screen-on-cmds {
        compatible = "rockchip,screen-on-cmds";
        rockchip,cmd_debug = <1>;
        rockchip,on-cmds1 { // refer to ⼀ Initialization commands 
                compatible = "rockchip,on-cmds";
                rockchip,cmd_type = <LPDT>; // The order is in  low power（LPDT） still  high speed（HSDT） Next send 
                rockchip,dsi_id = <2>;// Choose which mipi send out  0==》 single mipi0  1==》mipi1 2==》 double mipi0+1
                rockchip,cmd = <0x05 0x01>; // Initialization command 
                    // The first ⼀ Bytes  DSI  data type ;  The first ⼆ Bytes to  LCD  Of  CMD;  after ⾯ Is the instruction content 
                rockchip,cmd_delay = <0>;
        };

mipi rate
mipi_clk = resH * resW * 24 * 1.25 * fps / lane_num