Hi
I am debugging "EHCI host system error" (4.15.2.4) issue. The issue
happens during unlinking of URB from an interface driver. In our system
the device is always connected to the host. some interfaces are always
active (I/O can happen). Other interface's I/O depends on the user
space. if user opens the device node, we submit IN URB. This issue
happens when unlinking URB upon file close. This issue happens very rarely.
I have a doubt in unlink path of EHCI driver. Say if an endpoint has two
pending IN URB requests at the time of calling unlinking API.
(usb_kill_anchored_urbs API).
The QH's queue of this endpoint looks like this.
Qtd1 --> Qtd2 --> Dummy
EHCI driver kicks in the Async Advance Doorbell handshake after
manipulating the QH horizontal pointer in start_unlink_async() function.
EHCI driver wait for IAAD interrupt from the controller.
Say controller is working on Qtd1. Which means transfer overlay of this
QH has reference to Qtd2. controller generates IAAD interrupt (Qtd1 is
not completely finished. QH active pointer points to Qtd1). EHCI driver
finishes Qtd2 unlinking and points qtd1's next pointer to qtd'2 next
pointer and puts this QH back to asynchronous schedule.
My doubt is that software updated only QTD1 memory to point it to Qtd'2
next pointer i.e dummy. What about the QH's transfer overlay memory?
Would not the controller try to access the Qtd2 when QH is put back into
schedule.
To further clarify my question, I am copy pasting the qh_refresh() code
here. In the below code, if we enter "first qtd may already be partially
processed" case, should not we update qh->hw->hw_qtd_next and
qh->hw->hw_alt_next to reflect the current Qtd memory.
static void
qh_refresh (struct ehci_hcd *ehci, struct ehci_qh *qh)
{
struct ehci_qtd *qtd;
if (list_empty (&qh->qtd_list))
qtd = qh->dummy;
else {
qtd = list_entry (qh->qtd_list.next,
struct ehci_qtd, qtd_list);
/* first qtd may already be partially processed */
if (cpu_to_hc32(ehci, qtd->qtd_dma) == qh->hw->hw_current)
qtd = NULL;
}
if (qtd)
qh_update (ehci, qh, qtd);
}
Thanks,
Pavan
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