[U-Boot] [PATCH] usb_ether: register usb ethernet gadget at each eth init

[Vitaly Kuzmichev]

Hi Lei,

Lei Wen wrote:
> [...]
>>> For current ether.c state, there is no usb_gadget_unregister_driver in
>>> it. Even it has, we still need
>>> usb_gadget_register_driver call in each eth_init().
>>
>> Yes, if we do 'unregister' we should do 'register' somewhere before. If
>> we do 'register' we should do 'unregister' somewhere after.
>> This is the symmetry such like in dynamic data allocation (like
>> malloc/free), and we should comply it.
>> The reason why there is no 'usb_gadget_unregister_driver' in the Ether
>> driver yet is that there is no symmetrical function for
>> 'usb_eth_initialize' because there is no way to remove a network device
>> from the U-Boot environment.
>>
> What we need to do is not trying to remove the network device, but to register
> another gadget when we want to switch from tftp to fastboot, and make UDC take
> a different protocol to communicate with host.

I have not asked you to remove network device, I have talked about the
reason for the following:
> For current ether.c state, there is no usb_gadget_unregister_driver in
> it.

> [...]
>>> Right, if at the same time certainly need to return error.
>>
>> So your code that expects successful register will make Ether gadget
>> broken...
> 
> Don't understand here, why the Ether gadget would be broken?

Because UDC driver does not allow to register more than 1 gadget driver
in the same time. It just returns EBUSY. Even if the first gadget driver
is idle (when Ether gadget driver is registered but tftp command is not
issued). This is done to protect against memory leaks.
Just checkout  cdc-at91  branch in  u-boot-usb.git  for example of UDC
driver (drivers/usb/gadget/at91_udc.c). Or look at any UDC driver in
linux kernel.


> [...]
>> This means that if you want 2 gadgets you need to register each one
>> right before transferring data and unregister right after the data was
>> transferred. By doing gadget unregister you will free allocated
>> resources (such as USB endpoints and USB requests) in UDC and Ether
>> drivers properly. Otherwise you will have memory leaks.
> 
> Sure, so we comes into a conclusion that add register call in the
> eth_init and unregister call
> in eth_halt? In unregister call, the UDC driver should free the ep as you said.

Yes, it will free by 'eth_unbind' called from
'usb_gadget_unregister_driver'.

Note that 'usb_gadget_register_driver' should be removed from
'usb_eth_initialize' and dev->gadget checking should be added in eth_halt.

> 
> Best regards,
> Lei

Best regards,
Vitaly.