USB HOST和device切换原理--基于imx8qm

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USB_HOST_GADGET_SWITCH

相关文件

• kernel_imx\arch\arm64\boot\dts\freescale\fsl-imx8qm-mek-domu.dts: 如果开机固定为host模式，只需修改dr_mode = “host”;如果需要OTG功能切换，底层是根据ID PIN引脚的高低电平进行判断(host device),软件上通过otgsc register判断。

  &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: 由于我们ID脚悬空，则不适用OTG功能，在DTS中直接设置成host，则进入else判断分支。

  --------------------------------------------------
  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: 此为OTG功能时读取OTGSC寄存器进行判断。

  /**             * 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;elseval &= ~OTGSC_BSVIS;if (cable->connected)val |= OTGSC_BSV;elseval &= ~OTGSC_BSV;if (cable->enabled)val |= OTGSC_BSVIE;elseval &= ~OTGSC_BSVIE;}cable = &ci->platdata->id_extcon;if (!IS_ERR(cable->edev)) {if (cable->changed)val |= OTGSC_IDIS;elseval &= ~OTGSC_IDIS;if (cable->connected)val &= ~OTGSC_ID; /* host */elseval |= OTGSC_ID; /* device */if (cable->enabled)val |= OTGSC_IDIE;elseval &= ~OTGSC_IDIE;}return val & mask;
  }
  

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