Re: [Qemu-devel] [PATCH 13/31] usb-ehci: drop EXECUTING checks.

[David Ahern <daahern@cisco.com>]

On 06/06/2011 07:34 AM, David Ahern wrote:
> On 06/06/2011 06:39 AM, Gerd Hoffmann wrote:
>> The state machine doesn't stop in EXECUTING state any more when async
>> packets are in flight, so the checks are not needed any more and can
>> be dropped.
>>
>> Also kick out the check for the frame timer.  As we don't stop & sleep
>> any more on async packets this is obsolete.
>>
>> Signed-off-by: Gerd Hoffmann <kraxel@redhat.com>
>> ---
>>  hw/usb-ehci.c |   32 ++------------------------------
>>  1 files changed, 2 insertions(+), 30 deletions(-)
>>
>> diff --git a/hw/usb-ehci.c b/hw/usb-ehci.c
>> index e345a1c..8b1ae3a 100644
>> --- a/hw/usb-ehci.c
>> +++ b/hw/usb-ehci.c
>> @@ -1437,17 +1437,6 @@ static int ehci_state_fetchentry(EHCIState *ehci, int async)
>>      int again = 0;
>>      uint32_t entry = ehci_get_fetch_addr(ehci, async);
>>  
>> -#if EHCI_DEBUG == 0
>> -    if (qemu_get_clock_ns(vm_clock) / 1000 >= ehci->frame_end_usec) {
>> -        if (async) {
>> -            DPRINTF("FETCHENTRY: FRAME timer elapsed, exit state machine\n");
>> -            goto out;
>> -        } else {
>> -            DPRINTF("FETCHENTRY: WARNING "
>> -                    "- frame timer elapsed during periodic\n");
>> -        }
>> -    }
>> -#endif

This check was added to per Section 4 of the EHCI spec -- the HC should
not start transactions that will not be completed before the end of the
micro-frame. If you remove this what causes the EHCI model to take a
breather?

David


>>      if (entry < 0x1000) {
>>          DPRINTF("fetchentry: entry invalid (0x%08x)\n", entry);
>>          ehci_set_state(ehci, async, EST_ACTIVE);
>> @@ -1952,12 +1941,6 @@ static void ehci_advance_async_state(EHCIState *ehci)
>>          }
>>  
>>          ehci_set_state(ehci, async, EST_WAITLISTHEAD);
>> -        /* fall through */
>> -
>> -    case EST_FETCHENTRY:
>> -        /* fall through */
> 
> Why drop this case too? As I recall that is needed for proper execution.
> 
> David
> 
>> -
>> -    case EST_EXECUTING:
>>          ehci_advance_state(ehci, async);
>>          break;
>>  
>> @@ -2010,11 +1993,6 @@ static void ehci_advance_periodic_state(EHCIState *ehci)
>>          ehci_advance_state(ehci, async);
>>          break;
>>  
>> -    case EST_EXECUTING:
>> -        DPRINTF("PERIODIC state adv for executing\n");
>> -        ehci_advance_state(ehci, async);
>> -        break;
>> -
>>      default:
>>          /* this should only be due to a developer mistake */
>>          fprintf(stderr, "ehci: Bad periodic state %d. "
>> @@ -2063,11 +2041,7 @@ static void ehci_frame_timer(void *opaque)
>>          if (frames - i > 10) {
>>              skipped_frames++;
>>          } else {
>> -            // TODO could this cause periodic frames to get skipped if async
>> -            // active?
>> -            if (ehci_get_state(ehci, 1) != EST_EXECUTING) {
>> -                ehci_advance_periodic_state(ehci);
>> -            }
>> +            ehci_advance_periodic_state(ehci);
>>          }
>>  
>>          ehci->last_run_usec += FRAME_TIMER_USEC;
>> @@ -2082,9 +2056,7 @@ static void ehci_frame_timer(void *opaque)
>>      /*  Async is not inside loop since it executes everything it can once
>>       *  called
>>       */
>> -    if (ehci_get_state(ehci, 0) != EST_EXECUTING) {
>> -        ehci_advance_async_state(ehci);
>> -    }
>> +    ehci_advance_async_state(ehci);
>>  
>>      qemu_mod_timer(ehci->frame_timer, expire_time);
>>  }