USB HOST和device切換原理--基於imx8qm

USB_HOST_GADGET_SWITCH

相關文件

• kernel_imx\arch\arm64\boot\dts\freescale\fsl-imx8qm-mek-domu.dts: 如果開機固定爲host模式，只需修改dr_mode = “host”;如果需要OTG功能切換，底層是根據ID PIN引腳的高低電平進行判斷(host device),軟件上通過otgsc register判斷。

  &usbotg1 {
  	pinctrl-names = "default";
  	pinctrl-0 = <&pinctrl_usbotg1>;
  	srp-disable;
  	hnp-disable;
  	adp-disable;
  	power-polarity-active-high;
  	disable-over-current;
  	dr_mode = "host";
  	status = "okay";
  };
  

• kernel_imx/drivers/usb/common/common.c

  --------------------------------------------------
  platform_device->
      ci_get_platdata(dev, platdata);
          ->usb_get_dr_mode(dev);
  --------------------------------------------------
  
  enum usb_dr_mode usb_get_dr_mode(struct device *dev)
  {               
          const char *dr_mode;
          int err;
          
          err = device_property_read_string(dev, "dr_mode", &dr_mode);
          if (err < 0)
                  return USB_DR_MODE_UNKNOWN;
                  
          return usb_get_dr_mode_from_string(dr_mode);
  }       
  EXPORT_SYMBOL_GPL(usb_get_dr_mode); 
  
  

• kernel_imx\drivers\usb\chipidea\core.c: 由於我們ID腳懸空，則不適用OTG功能，在DTS中直接設置成host，則進入else判斷分支。

  --------------------------------------------------
  ci_hdrc_probe->
      -> ci->role = ci_get_role(ci);
  --------------------------------------------------    
  static enum ci_role ci_get_role(struct ci_hdrc *ci)
  {
  	if (ci->roles[CI_ROLE_HOST] && ci->roles[CI_ROLE_GADGET]) {
  		if (ci->is_otg) {
  			hw_write_otgsc(ci, OTGSC_IDIE, OTGSC_IDIE);
  			return ci_otg_role(ci);
  		} else {
  			/*
  			 * If the controller is not OTG capable, but support
  			 * role switch, the defalt role is gadget, and the
  			 * user can switch it through debugfs.
  			 */
  			return CI_ROLE_GADGET;
  		}
  	} else {
  		return ci->roles[CI_ROLE_HOST]
  			? CI_ROLE_HOST
  			: CI_ROLE_GADGET;
  	}
  }
  

• kernel_imx/drivers/usb/chipidea/otg.c: 此爲OTG功能時讀取OTGSC寄存器進行判斷。

  /**             
   * ci_otg_role - pick role based on ID pin state
   * @ci: the controller  
   */             
  enum ci_role ci_otg_role(struct ci_hdrc *ci)
  {
          enum ci_role role = hw_read_otgsc(ci, OTGSC_ID)
                  ? CI_ROLE_GADGET
                  : CI_ROLE_HOST;
                          
          return role;
  }  
  
  /**
   * hw_read_otgsc returns otgsc register bits value.
   * @mask: bitfield mask
   */
  u32 hw_read_otgsc(struct ci_hdrc *ci, u32 mask)
  {
          struct ci_hdrc_cable *cable;
          u32 val = hw_read(ci, OP_OTGSC, mask);
  
          /*
           * If using extcon framework for VBUS and/or ID signal
           * detection overwrite OTGSC register value
           */
          cable = &ci->platdata->vbus_extcon;
          if (!IS_ERR(cable->edev)) {
                  if (cable->changed)
                          val |= OTGSC_BSVIS;
                  else
                          val &= ~OTGSC_BSVIS;
  
                  if (cable->connected)
                          val |= OTGSC_BSV;
                  else
                          val &= ~OTGSC_BSV;
  
                  if (cable->enabled)
                          val |= OTGSC_BSVIE;
                  else
                          val &= ~OTGSC_BSVIE;
          }
  
          cable = &ci->platdata->id_extcon;
          if (!IS_ERR(cable->edev)) {
                  if (cable->changed)
                          val |= OTGSC_IDIS;
                  else
                          val &= ~OTGSC_IDIS;
  
                  if (cable->connected)
                          val &= ~OTGSC_ID; /* host */
                  else
                          val |= OTGSC_ID; /* device */
  
                  if (cable->enabled)
                          val |= OTGSC_IDIE;
                  else
                          val &= ~OTGSC_IDIE;
          }
  
          return val & mask;
  }