On Thu, 25 Jun 2009 00:26:54 +0800
Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 24 Jun 2009, Alek Du wrote:
> >
> > No, Alan,
> >
> > union ehci_shadow {
> > struct ehci_qh_hw *qh_hw; /* Q_TYPE_QH */
> > struct ehci_itd *itd; /* Q_TYPE_ITD */
> > struct ehci_sitd *sitd; /* Q_TYPE_SITD */
> > struct ehci_fstn *fstn; /* Q_TYPE_FSTN */
> > __hc32 *hw_next; /* (all types) */
> > void *ptr;
> > };
> >
> > the *hw_next requires all hardware structure here. There a lot codes that compare this with hw_next in HCD.
>
> Can you give any examples where this would matter?
>
> > The hw_next is the first item for the 4 kinds of descriptors.
>
> I know. That doesn't mean the shadow pointer has to point to the
> hw_next field when it points to a QH.
>
Here is the example, the here.hw_next must be a __hc32 in EHCI HW periodic list.
static void periodic_unlink (struct ehci_hcd *ehci, unsigned frame, void *ptr)
{
union ehci_shadow *prev_p = &ehci->pshadow[frame];
__hc32 *hw_p = &ehci->periodic[frame];
union ehci_shadow here = *prev_p;
/* find predecessor of "ptr"; hw and shadow lists are in sync */
while (here.ptr && here.ptr != ptr) {
prev_p = periodic_next_shadow(ehci, prev_p,
Q_NEXT_TYPE(ehci, *hw_p));
hw_p = here.hw_next;
here = *prev_p;
}
static union ehci_shadow *
periodic_next_shadow(struct ehci_hcd *ehci, union ehci_shadow *periodic,
__hc32 tag)
{
switch (hc32_to_cpu(ehci, tag)) {
case Q_TYPE_QH:
return &periodic->qh->qh_next;
case Q_TYPE_FSTN:
return &periodic->fstn->fstn_next;
case Q_TYPE_ITD:
return &periodic->itd->itd_next;
// case Q_TYPE_SITD:
default:
return &periodic->sitd->sitd_next;
}
}
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