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

[Sherry Sun]

Hi Marek,

> 
> 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.

Okay, you are right, I will add this flag, thanks.

Best regards
Sherry sun