Re: usb hcd questions

On 10/25/07, Alan Stern <[email protected]> wrote:
> On Wed, 24 Oct 2007, jidong xiao wrote:
>
> > 1.I noticed there is a new root-hub polling mechanism,what is it?And
> > what is the old one?
>
> The old polling mechanism calls the HCD's hub_status_data routine only
> when a status URB is pending.  The new polling mechanism calls the
> HCD's hub_status_data routine whenever requested to do, regardless of
> whether or not a status URB is pending.
>
> > 2.struct usb_hcd has an element of unsigned poll_pending, what does
> > this variable mean?
>
> It means the HCD's hub_status_data routine has said a root-hub status
> change occurred, but no status URB was submitted so the status change
> couldn't be sent upward to the hub driver.  When the next status URB is
> submitted, it will complete almost immediately with the new status
> information.
>
> >  In particular, this method sets poll_pending:
> >
> > void usb_hcd_poll_rh_status(struct usb_hcd *hcd){
> > ...
> >               if (length > 0)
> >                       usb_hcd_giveback_urb (hcd, urb);
> >               else
> >                       hcd->poll_pending = 1;
> > }
> >
> > Why for length<=0, we need to set hcd->poll_pending to 1?
>
> The code above is old.  Still, the idea is what I wrote above.  If
> length <= 0 then there is no status URB currently queued.
> hcd->poll_pending has to be set so that when the next status URB is
> submitted it can get the status-change information quickly.  If we
> didn't do this then the URB might not complete for a long time, since
> root-hub status changes are often interrupt-driven and there might not
> be any status interrupts for a while.
>
Regarding "since root-hub status changes are often interrupt-driven"...

Not quite understand about this,actually I saw in several place of the
source code, we still set poll_rh to 1,as I understand,usbcore will
poll for events whenever poll_rh is set. So if HCD often uses
interrupt to get root hub events, then under what condition,we need to
use poll?

Take uhci-hcd for example, note that, poll_rh is set inside
start_rh/uhci_resume, why the root hub needs to be polled at these
circumstances?

Regards
Jason

-------------------------------------------------------------------------
This SF.net email is sponsored by: Splunk Inc.
Still grepping through log files to find problems?  Stop.
Now Search log events and configuration files using AJAX and a browser.
Download your FREE copy of Splunk now >> http://get.splunk.com/
_______________________________________________
[email protected]
To unsubscribe, use the last form field at:
https://lists.sourceforge.net/lists/listinfo/linux-usb-devel