On Wed, 24 Jun 2009, Alek Du wrote:
> > You really have two choices for the shadow pointers. You can keep the
> > pointer to the hardware structure (as you did here), or you could store
> > the pointer to the software structure instead.
> >
> > It seems likely that the patch would be simpler if you took the second
> > choice. (You might even find that you never need to use the
> > backpointer from ehci_qh_hw to ehci_qh!) Have you considered doing it
> > this way?
>
> 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.
Alan Stern
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