MIPI DSI

Overview

The Display Serial Interface (DSI) is a specification developed by the Mobile Industry Processor Interface (MIPI) Alliance to reduce the cost of display controllers in mobile devices. In the Hardware Driver Foundation (HDF), the MIPI DSI module uses the service-free mode for API adaptation. The service-free mode applies to the devices that do not provide user-mode APIs or the operating system (OS) that does not distinguish the user mode and the kernel mode. In the service-free mode, DevHandle (a void pointer) directly points to the kernel-mode address of the device object.

Figure 1 Service-free mode

Available APIs

MipiDsiCntlrMethod:

struct MipiDsiCntlrMethod { // Member functions of the core layer structure
    int32_t (*setCntlrCfg)(struct MipiDsiCntlr *cntlr);
    int32_t (*setCmd)(struct MipiDsiCntlr *cntlr, struct DsiCmdDesc *cmd);
    int32_t (*getCmd)(struct MipiDsiCntlr *cntlr, struct DsiCmdDesc *cmd, uint32_t readLen, uint8_t *out);
    void (*toHs)(struct MipiDsiCntlr *cntlr);
    void (*toLp)(struct MipiDsiCntlr *cntlr);
    void (*enterUlps)(struct MipiDsiCntlr *cntlr);                      // (Optional) Enter the Ultra-Low Power State (ULPS).
    void (*exitUlps)(struct MipiDsiCntlr *cntlr);                       // (Optional) Exit the ULPS.
    int32_t (*powerControl)(struct MipiDsiCntlr *cntlr, uint8_t enable);// (Optional) Enable or disable power control.
    int32_t (*attach)(struct MipiDsiCntlr *cntlr);                      // (Optional) Attach a DSI device to the host.
};

Table 1 Description of the callback functions in MipiDsiCntlrMethod

How to Develop

The MIPI DSI module adaptation involves the following steps:

1. Configure attribute files.

   • Add the deviceNode description to the device_info.hcs file.
   • (Optional) Add the mipidsi_config.hcs file.

2. Instantiate the driver entry.

   • Instantiate the HdfDriverEntry structure.
   • Call HDF_INIT to register the HdfDriverEntry instance with the HDF.

3. Instantiate the MIPI DSI controller object.

   • Initialize MipiDsiCntlr.
   • Instantiate MipiDsiCntlrMethod in the MipiDsiCntlr object.

     NOTE
     For details about the functions in MipiDsiCntlrMethod, see Available APIs.

4. Debug the driver.

   (Optional) For new drivers, verify basic functions, for example, check the information returned after the driver is attached and whether data is successfully transmitted.

Development Example

The following uses mipi_tx_hi35xx.c as an example to present the contents that need to be provided by the vendor to implement device functions.

1. Configure the device attributes in xx_config.hcs and add the deviceNode information to the device_info.hcs file.

   The device attribute values are closely related to the default values or value range of the MipiDsiCntlr members at the core layer. The deviceNode information is related to the driver entry registration.

   In this example, no additional attribute needs to be configured for the MIPI DSI controller. If required, add the deviceMatchAttr information to deviceNode in the device_info file and add the mipidsi_config file.

   device_info.hcs configuration example:

   root {
   device_info {
       match_attr = "hdf_manager";
       platform :: host {
       hostName = "platform_host";
       priority = 50;
       device_mipi_dsi:: device {
           device0 :: deviceNode {
           policy = 0;
           priority = 150;
           permission = 0644;
           moduleName = "HDF_MIPI_TX";    // (Mandatory) Driver name, which must be the same as moduleName in the driver entry.
           serviceName = "HDF_MIPI_TX";   // (Mandatory) Unique name of the service published by the driver.
           }
       }
       }
   }
   }
   

2. Instantiate the driver entry.

   The driver entry must be a global variable of the HdfDriverEntry type (defined in hdf_device_desc.h), and the value of moduleName must be the same as that in device_info.hcs. The function pointer members in the HdfDriverEntry structure are filled by the vendors' operation functions. In the HDF, the start address of each HdfDriverEntry object of all loaded drivers is collected to form a segment address space similar to an array for the upper layer to invoke.

   Generally, the HDF calls the Bind function and then the Init function to load a driver. If Init fails to be called, the HDF calls Release to release driver resources and exit.

   MIPI DSI driver entry example:

   struct HdfDriverEntry g_mipiTxDriverEntry = {
       .moduleVersion = 1,             
       .Init = Hi35xxMipiTxInit,       // See the Init function.
       .Release = Hi35xxMipiTxRelease, // See the Release function.
       .moduleName = "HDF_MIPI_TX",    // (Mandatory) The value must be the same as that in the device_info.hcs file.
   };
   HDF_INIT(g_mipiTxDriverEntry);      // Call HDF_INIT to register the driver entry with the HDF.
   

3. Initialize the MipiDsiCntlr object at the core layer, including defining a custom structure (to pass parameters and data) and implementing the HdfDriverEntry member functions (Bind, Init and Release) to instantiate MipiDsiCntlrMethod in MipiDsiCntlr (so that the underlying driver functions can be called).

   • Defining a custom structure

     To the driver, the custom structure holds parameters and data. Generally, the values in the config file are used to initialize the structure members. However, in this example, the MIPI DSI has no device attribute file. Therefore, the basic member structure is similar to that of MipiDsiCntlr.

     typedef struct {
       unsigned int devno;                   // Device number
       short           laneId[LANE_MAX_NUM]; // Lane ID
       OutPutModeTag   outputMode;           // Output mode, which can be CSI mode, DSI Video mode, or DSI Command mode.
       VideoModeTag    videoMode;            // Synchronization mode of the display device
       OutputFormatTag outputFormat;         // Format of the output DSI image, which can be RGB or YUV.
       SyncInfoTag syncInfo;                 // Settings related to timing
       unsigned int phyDataRate;             // Data rate, in Mbit/s
       unsigned int    pixelClk;             // Clock, in kHz
     } ComboDevCfgTag;
     
     // MipiDsiCntlr is the controller structure at the core layer. The Init function assigns values to the members of MipiDsiCntlr.
     struct MipiDsiCntlr {
       struct IDeviceIoService service;
       struct HdfDeviceObject *device;
       unsigned int devNo;         // Device number
       struct MipiCfg cfg;
       struct MipiDsiCntlrMethod *ops;
       struct OsalMutex  lock;
       void *priv;
     };
     

   • Instantiating MipiDsiCntlrMethod in MipiDsiCntlr (other members are initialized by Init)

     static struct MipiDsiCntlrMethod g_method = {
         .setCntlrCfg = Hi35xxSetCntlrCfg,
         .setCmd = Hi35xxSetCmd,
         .getCmd = Hi35xxGetCmd,
         .toHs = Hi35xxToHs,
         .toLp = Hi35xxToLp,
     };
     

   • Init function

     Input parameter:

     HdfDeviceObject, an interface parameter exposed by the driver, contains the .hcs information.

     Return value:

     HDF_STATUS

     The table below describes some status. For more information, see HDF_STATUS in the /drivers/framework/include/utils/hdf_base.h file.

 **Function description**:

 Attaches the **MipiDsiCntlrMethod** instance, calls **MipiDsiRegisterCntlr**, and performs other vendor-defined initialization operations.

 ```
  static int32_t Hi35xxMipiTxInit(struct HdfDeviceObject *device)
  {
  int32_t ret;
  g_mipiTx.priv = NULL;                         // g_mipiTx is a global variable defined.
                                                 // static struct MipiDsiCntlr g_mipiTx { 
                                                 //     .devNo=0
                                                 //};
  g_mipiTx.ops = &g_method;                     // Attach the MipiDsiCntlrMethod instance.
  ret = MipiDsiRegisterCntlr(&g_mipiTx, device);// (Mandatory) Call the function at the core layer and g_mipiTx to initialize global variables at the core layer.
  ...
  return MipiTxDrvInit(0);                      // (Mandatory) Device initialization customized by the vendor.
  }
   
  // mipi_dsi_core.c file
  int32_t MipiDsiRegisterCntlr(struct MipiDsiCntlr *cntlr, struct HdfDeviceObject *device)
  {
  ...
  // Define the global variable static struct MipiDsiHandle g_mipiDsihandle[MAX_CNTLR_CNT].
  if (g_mipiDsihandle[cntlr->devNo].cntlr == NULL) {
      (void)OsalMutexInit(&g_mipiDsihandle[cntlr->devNo].lock);
      (void)OsalMutexInit(&(cntlr->lock));
   
      g_mipiDsihandle[cntlr->devNo].cntlr = cntlr;// Initialize MipiDsiHandle.
      g_mipiDsihandle[cntlr->devNo].priv = NULL;  
      cntlr->device = device;                     // Prerequisites for conversion between HdfDeviceObject and MipiDsiHandle.
      device->service = &(cntlr->service);       // Prerequisites for conversion between HdfDeviceObject and MipiDsiHandle.
      cntlr->priv = NULL;    
      ...
      return HDF_SUCCESS;
  }
  ...
  return HDF_FAILURE;
  }
 ```

• Release function

  Input parameter:

  HdfDeviceObject, an interface parameter exposed by the driver, contains the .hcs information.

  Return value:

  No value is returned.

  Function description:

  Releases the memory and deletes the controller. This function assigns values to the Release API in the driver entry structure. When the HDF fails to call the Init function to initialize the driver, the Release function can be called to release driver resources.

  NOTE

  All forced conversion operations for obtaining the corresponding object can be successful only when the Init function has the corresponding value assignment operations.

   static void Hi35xxMipiTxRelease(struct HdfDeviceObject *device)
   {
   struct MipiDsiCntlr *cntlr = NULL;
   ...
   cntlr = MipiDsiCntlrFromDevice(device);// A forced conversion from HdfDeviceObject to MipiDsiCntlr is involved.
                                            // return (device == NULL) ? NULL : (struct MipiDsiCntlr *)device->service;
   ...
   MipiTxDrvExit(;                        // (Mandatory) Release the resources occupied by the vendor's devices.
   MipiDsiUnregisterCntlr(&g_mipiTx);     // Empty function
   g_mipiTx.priv = NULL;
   HDF_LOGI("%s: unload mipi_tx driver 1212!", __func__);
   }