Re: [PATCH v6] usb: Adding SuperSpeed support to dummy_hcd

[Alan Stern]

On Thu, 18 Nov 2010, Tatyana Brokhman wrote:

> USB 3.0 hub includes 2 hubs - HS and SS ones.
> Thus, when dummy_hcd enabled it will register 2 root hubs (SS and HS).

Hmm.  A quick comparison with the original source shows that you
neglected to add code for SuperSpeed transfers to periodic_bytes() and
show_urb().

> @@ -1352,6 +1544,9 @@ static void dummy_timer (unsigned long _dum)
>  	case USB_SPEED_HIGH:
>  		total = 512/*bytes*/ * 13/*packets*/ * 8/*uframes*/;
>  		break;
> +	case USB_SPEED_SUPER:
> +		total = 400 << 20; /* 400MB = 400*(2^20) bytes */
> +		break;

Somehow I doubt that SuperSpeed USB, quick though it is, can transfer
400 MB in one millisecond.  Where did you get that number from?

I can't find the appropriate table in the USB-3.0 spec (it might not be
there at all), but with a bus transfer rate of 500 million bytes/s it
seems clear that you can't transfer more than 500000 bytes per frame.  
The actual limit must be lower than that, maybe something like 1024
bytes/packet * 60 packets/uframe * 8 uframes/frame = 491520 
bytes/frame.

Alan Stern

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