Part of the emulation performed by dummy-hcd is accounting for
bandwidth utilization. The total amount of data transferred in a
single frame is supposed to be no larger than an actual USB connection
could accommodate.
Currently the driver performs bandwidth limiting only for bulk
transfers; control and periodic transfers are effectively unlimited.
(Presumably drivers were not expected to request extremely large
control or interrupt transfers.) This patch improves the situation
somewhat by restricting them as well.
The emulation still isn't perfect. On a real system, even 0-length
transfers use some bandwidth because of transaction overhead
(IN, OUT, ACK, NACK packets) and packet overhead (SYNC, PID, bit
stuffing, CRC, EOP). Adding in those factors is left as an exercise
for a later patch.
Signed-off-by: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx>
---
[as1848]
drivers/usb/gadget/udc/dummy_hcd.c | 12 ++++--------
1 file changed, 4 insertions(+), 8 deletions(-)
Index: usb-4.x/drivers/usb/gadget/udc/dummy_hcd.c
===================================================================
--- usb-4.x.orig/drivers/usb/gadget/udc/dummy_hcd.c
+++ usb-4.x/drivers/usb/gadget/udc/dummy_hcd.c
@@ -1780,6 +1780,7 @@ static void dummy_timer(unsigned long _d
int i;
/* simplistic model for one frame's bandwidth */
+ /* FIXME: account for transaction and packet overhead */
switch (dum->gadget.speed) {
case USB_SPEED_LOW:
total = 8/*bytes*/ * 12/*packets*/;
@@ -1824,7 +1825,6 @@ restart:
struct dummy_request *req;
u8 address;
struct dummy_ep *ep = NULL;
- int type;
int status = -EINPROGRESS;
/* stop when we reach URBs queued after the timer interrupt */
@@ -1836,14 +1836,10 @@ restart:
goto return_urb;
else if (dum_hcd->rh_state != DUMMY_RH_RUNNING)
continue;
- type = usb_pipetype(urb->pipe);
- /* used up this frame's non-periodic bandwidth?
- * FIXME there's infinite bandwidth for control and
- * periodic transfers ... unrealistic.
- */
- if (total <= 0 && type == PIPE_BULK)
- continue;
+ /* Used up this frame's bandwidth? */
+ if (total <= 0)
+ break;
/* find the gadget's ep for this request (if configured) */
address = usb_pipeendpoint (urb->pipe);
--
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