Re: [PATCH v7 1/5] usb: Adding SuperSpeed support to dummy_hcd
From: Alan Stern
Date: Thu Jan 27 2011 - 11:27:31 EST
On Thu, 27 Jan 2011, Tatyana Brokhman wrote:
> This patch adds SS support to the dummy hcd module. It may be used to test
> SS device when no (SS) HW is available.
> USB 3.0 hub includes 2 hubs - HS and SS ones.
> This patch adds support for a SS hub in the dummy_hcd module. Thus, when
> dummy_hcd enabled it will register 2 root hubs (SS and HS).
Getting there. A few spots could still use some attention.
Also, you might try running this patch through checkpatch.pl and fixing
any complaints it makes.
> @@ -343,7 +431,13 @@ dummy_enable (struct usb_ep *_ep, const struct usb_endpoint_descriptor *desc)
> dum = ep_to_dummy (ep);
> if (!dum->driver || !is_enabled (dum))
> return -ESHUTDOWN;
> - max = le16_to_cpu(desc->wMaxPacketSize) & 0x3ff;
> + max = le16_to_cpu(desc->wMaxPacketSize) ;
> + /*
> + * For HS/FS devices only bits 0..9 of the wMaxPacketSize represent the
> + * maximum packet size
> + */
> + if (dum->gadget.speed < USB_SPEED_SUPER)
> + max &= 0x3ff;
Strictly speaking, both the old and the new code are wrong. For all
devices, regardless of speed, we should say:
max = le16_to_cpu(desc->wMaxPacketSize) & 0x7ff;
In other words, the speed is contained in bits 0..10 (not 0..9).
> @@ -1352,6 +1559,10 @@ static void dummy_timer (unsigned long _dum)
> case USB_SPEED_HIGH:
> total = 512/*bytes*/ * 13/*packets*/ * 8/*uframes*/;
> + case USB_SPEED_SUPER:
> + /* 400MBps = 400*(2^20)/1000 bytes per milisec */
> + total = (400 << 20) / 1000;
> + break;
Ugh. For one thing, SuperSpeed runs at 500 million bytes/s, not 400
million. For another, 400 << 20 isn't equal to 400 million.
Don't try to be too clever. Realizing that this is only an
approximation anyway, just say:
/* Bus speed is 500000 bytes/ms, so use a little less */
total = 490000;
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