Re: New USB core API to change interval and max packet size

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Em Wed, 02 Oct 2013 11:00:13 -0400 (EDT)
Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> escreveu:

> On Wed, 2 Oct 2013, Mauro Carvalho Chehab wrote:
> 
> > Let me see if I understand the changes at the media drivers. So, please
> > correct me if I got it wrong.
> > 
> > I'm yet to get any USB 3.0 media device, although it is common to connect
> > an USB 1.1 or USB 2.0 device on a USB 3.0 host port.
> > 
> > So, for example, on this device:
> 
> > ...
> > 	      Endpoint Descriptor:
> > 	        bLength                 7
> > 	        bDescriptorType         5
> > 	        bEndpointAddress     0x83  EP 3 IN
> > 	        bmAttributes            3
> > 	          Transfer Type            Interrupt
> > 	          Synch Type               None
> > 	          Usage Type               Data
> > 	        wMaxPacketSize     0x0004  1x 4 bytes
> > 	        bInterval               1
> > ...
> > 
> > connected via this BUS device:
> 
> ...
> 
> > In such situation, and assuming that the USB tables are correct, there's
> > nothing that needs to be done there, as bInterval/wMaxPacketSize are
> > correct for USB 2.0.
> > 
> > So, there's no need to call usb_change_ep_bandwidth().
> 
> That's right.
> 
> > If so, then usb_change_ep_bandwidth() as a quirk, if bInterval
> > or wMaxPacketSize were improperly filled.
> > 
> > Right?
> 
> Or if the values are correct, but the driver wants to use something 
> different for its own reasons (for example, to get lower latency or 
> because it knows that it will never use packets as large as the 
> descriptor allows).  Right.

Ok, so, in this case, usb_change_ep_bandwidth() could be called
just before usb_alloc_urb(), in order to make it to use the packet
size that would be expected for that kind of ISOC traffic that
userspace indirectly selected, by adjusting the streaming
video resolution selected, right?

Regards,
Mauro
--
To unsubscribe from this list: send the line "unsubscribe linux-usb" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at  http://vger.kernel.org/majordomo-info.html




[Index of Archives]     [Linux Media]     [Linux Input]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [Old Linux USB Devel Archive]

  Powered by Linux