Re: [Qemu-devel] [PATCH] ohci: don't die on ED_LINK_LIMIT overflow

[Laurent Vivier]

On 21/03/2019 11:15, BALATON Zoltan wrote:
> On Thu, 21 Mar 2019, Laurent Vivier wrote:
>> Stop processing the descriptor list instead. The next frame timer tick
>> will
>> resume the work
> 
> Shoud this log something when the limit is reached to let the user know
> why USB stopped working instead of silently ignoring frames?

I don't think frames are ignored, they are only delayed. The aim of
ED_LINK_LIMIT is to avoid an infinite loop inside QEMU.

Thanks,
Laurent

> Regards,
> BALATON Zoltan
> 
>> Buglink: https://bugzilla.redhat.com/show_bug.cgi?id=1686705
>> Suggested-by: Gerd Hoffmann <address@hidden>
>> Signed-off-by: Laurent Vivier <address@hidden>
>> ---
>> hw/usb/hcd-ohci.c | 7 +------
>> 1 file changed, 1 insertion(+), 6 deletions(-)
>>
>> diff --git a/hw/usb/hcd-ohci.c b/hw/usb/hcd-ohci.c
>> index 196a9f72002d..81cf5ab7a5a7 100644
>> --- a/hw/usb/hcd-ohci.c
>> +++ b/hw/usb/hcd-ohci.c
>> @@ -1200,7 +1200,7 @@ static int ohci_service_ed_list(OHCIState *ohci,
>> uint32_t head, int completion)
>>     if (head == 0)
>>         return 0;
>>
>> -    for (cur = head; cur; cur = next_ed) {
>> +    for (cur = head; cur && link_cnt++ < ED_LINK_LIMIT; cur = next_ed) {
>>         if (ohci_read_ed(ohci, cur, &ed)) {
>>             trace_usb_ohci_ed_read_error(cur);
>>             ohci_die(ohci);
>> @@ -1209,11 +1209,6 @@ static int ohci_service_ed_list(OHCIState
>> *ohci, uint32_t head, int completion)
>>
>>         next_ed = ed.next & OHCI_DPTR_MASK;
>>
>> -        if (++link_cnt > ED_LINK_LIMIT) {
>> -            ohci_die(ohci);
>> -            return 0;
>> -        }
>> -
>>         if ((ed.head & OHCI_ED_H) || (ed.flags & OHCI_ED_K)) {
>>             uint32_t addr;
>>             /* Cancel pending packets for ED that have been paused.  */
>>