Re: [V2 PATCH 02/10] added media agnostic (MA) USB HCD roothubs

[Alan Stern <stern@rowland.harvard.edu>]

On Wed, 12 Nov 2014, Sean O. Stalley wrote:

> > > --- /dev/null
> > > +++ b/drivers/staging/mausb/drivers/mausb_hub.c
> > 
> > > +/**
> > > + * Returns true if the given is the superspeed HCD. Note: The primary HCD is
> > > + * High Speed and the shared HCD is SuperSpeed.
> > > + */
> > 
> > Why in that order?
> > 
> 
> We should probably switch this & make the superspeed hub primary.
> That way we match the xhci driver.

xhci-hcd makes the high-speed hcd the primary one.  This is because it 
registers the high-speed hcd before the SuperSpeed hcd.  There was a 
good reason for doing it this way, but I can't remember what it was 
(it's buried somewhere in the email archives).

That's why when you look at the output from lsusb or something similar,
a SuperSpeed root hub has a bus number that is one higher than its peer
high-speed root hub.

> > > +int mausb_hub_status_data(struct usb_hcd *hcd, char *buf)
> > > +{
> > > +	int                      i;
> > > +	u16                      port_change = 0;
> > > +	u32                      status = 0;
> > > +	int                      ret = 1;
> > > +	struct mausb_hcd	 *mhcd = usb_hcd_to_mausb_hcd(hcd);
> > > +	struct mausb_root_hub	 *roothub = usb_hcd_to_roothub(hcd);
> > > +
> > > +	/*
> > > +	 * Buf should never be more that 2 bytes. USB 3.0 hubs cannot have
> > > +	 * more than 15 downstream ports.
> > > +	 */
> > > +	buf[0] = 0;
> > > +	if (MAUSB_ROOTHUB_NUM_PORTS > 7) {
> > > +		buf[1] = 0;
> > > +		ret++;
> > > +	}
> > 
> > Endianness bug.
> > 
> 
> Could you elaborate?
> It was my understanding that this buffer was host-endian.
> Is this an unacceptable way to clear the buffer?

I don't understand Oliver's objection here.  The buffer is 
little-endian, just as it is for real hubs.  The code seems correct.

Alan Stern