Hi all,
The following code in qh_link_async:
if (!head->qh_next.qh) {
u32 cmd = ehci_readl(ehci, &ehci->regs->command);
if (!(cmd & CMD_ASE)) {
/* in case a clear of CMD_ASE didn't take yet */
(void)handshake(ehci, &ehci->regs->status,
STS_ASS, 0, 150);
cmd |= CMD_ASE | CMD_RUN;
ehci_writel(ehci, cmd, &ehci->regs->command);
ehci_to_hcd(ehci)->state = HC_STATE_RUNNING;
/* posted write need not be known to HC yet ... */
}
}
Why only the null queue head is checked? I think it is
possible that non-empty queue head link list also have asynchronous
list disabled
(hc encounter queue head of which H=1 and scan_async havent's
unlink the queue head).
If the non-empty queue head list condition is met, and
qh_link_async add new queue head directly without enable CMD_ASE &
CMD_RUN.
The host controller will not go ahead to process the new queue
head?? or if it's possible that hc could enable CMD_ASE & CMD_RUN in
other place ??
Could someone please tell me how this work ??
Regards,
Gavin Guo
--
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
