[U-Boot] [PATCH v4 2/4] USB: host: Add the USB3 host driver

[Marek Vasut]

On 8/20/19 5:42 PM, Sherry Sun wrote:
[...]

>>>>>>> +U_BOOT_DRIVER(xhci_imx8) = {
>>>>>>> +	.name	= "xhci_imx8",
>>>>>>> +	.id	= UCLASS_USB,
>>>>>>> +	.of_match = xhci_usb_ids,
>>>>>>> +	.probe = xhci_imx8_probe,
>>>>>>> +	.remove = xhci_imx8_remove,
>>>>>>> +	.ops	= &xhci_usb_ops,
>>>>>>> +	.platdata_auto_alloc_size = sizeof(struct usb_platdata),
>>>>>>> +	.priv_auto_alloc_size = sizeof(struct xhci_ctrl),
>>>>>>> +	.flags	= DM_FLAG_ALLOC_PRIV_DMA,
>>>>>>
>>>>>> I think you also need DM_FLAG_OS_PREPARE to trigger .remove before
>>>>>> booting Linux, but I might be wrong. Please check that.
>>>>>
>>>>> When use usb stop command to stop the usb host driver,
>>>>> device_remove(bus, DM_REMOVE_NORMAL) is called by usb_stop(), so
>>>>> normally we don’t need the DM_FLAG_OS_PREPARE flag.
>>>>> But considering some special circumstances, maybe add this flag is helpful.
>>>>
>>>> I'm not talking about "usb stop", I am talking about booting Linux.
>>>> That's when then .remove should be called to tear down the driver. Is it?
>>>
>>> I know what you mean. The only function of DM_FLAG_OS_PREPARE is to
>>> call .remove before booting kernel, to make sure the device is
>>> removed.
>>> But normally, the host device is removed every time after we use it.
>>
>> How so ? The controller is left running until you call .remove()
> 
> We usually start the host driver in uboot by using the usb start command, right?
> And we will call usb stop command to finish the usb start command.
> .remove will be called in usb_stop(). So I think the controller has already been teared before booting kernel.

That is only if you assume that every user will manually call usb stop,
always, and never fail to do so. And also every piece of code which
might have inited the USB will also tear down the controller. That is
not realistic.

Hence. you should call the .remove() before boot to tear down the
controller.