Re: [PATCH v2] char: xillybus: Check endpoint type before allocing

[Eli Billauer]

On 23/05/22 20:15, Greg KH wrote:
> > Rather, it works like this: The driver uses the EP 1 IN and OUT endpoints to
> > >  query the device for a data structure, which contains information on the
> > >  device's communication channels. The driver sets up device files
> > >  accordingly, and it also gets informed on which bulk OUT endpoints are
> > >  present.
> > >  
> > >  For what it's worth, I think it's fairly safe to assume that if a device
> > >  returns a legal data structure (which passes a CRC test), it's a XillyUSB
> > >  device.
> >      
> Why?  You still need to verify that the requested endpoints match up
> with what the device really has.
>    
OK. So to summarize:

EP 1 IN and EP 1 OUT are always present in XillyUSB devices.

On top of these, there might be additional bulk OUT endpoints. The 
driver resolves which ones in setup_channels(), by scanning a data blob 
it has received from the device. This takes place in the for-loop inside 
this function. When (out_desc & 0x80) is true for a given @i in the 
loop, the device has a bulk OUT endpoint with address i+2 (e.g. if this 
condition is met for i==2, the device has a bulk OUT EP 4).

So it seems like setup_channels() would be the right place to make this 
check, since it's called during the device's probe.

I guess it would likewise make sense to check for EP 1 IN and OUT in 
xillyusb_setup_base_eps().

Thanks,
   Eli