Re: [Qemu-devel] [qemu-s390x] [PATCH for-4.1 1/2] s390x/pci: add some fallthrough annotations

[Cornelia Huck <cohuck@redhat.com>]

On Wed, 17 Jul 2019 08:52:54 -0400
Collin Walling <walling@linux.ibm.com> wrote:

> On 7/17/19 5:27 AM, Christian Borntraeger wrote:
> > 
> > 
> > On 17.07.19 10:54, Cornelia Huck wrote:  
> >> On Tue, 16 Jul 2019 14:34:22 -0400
> >> Collin Walling <walling@linux.ibm.com> wrote:
> >>  
> >>> On 7/16/19 11:20 AM, Cornelia Huck wrote:  
> >>>> On Wed, 10 Jul 2019 10:20:41 +0200
> >>>> Cornelia Huck <cohuck@redhat.com> wrote:
> >>>>      
> >>>>> On Tue, 9 Jul 2019 18:55:34 -0400
> >>>>> Collin Walling <walling@linux.ibm.com> wrote:
> >>>>>     
> >>>>>> On 7/8/19 9:23 AM, Christian Borntraeger wrote:  
> >>>>>>>
> >>>>>>>
> >>>>>>> On 08.07.19 14:54, Cornelia Huck wrote:  
> >>>>>>>> According to the comment, the bits are supposed to accumulate.
> >>>>>>>>
> >>>>>>>> Reported-by: Stefan Weil <sw@weilnetz.de>
> >>>>>>>> Fixes: 5d1abf234462 ("s390x/pci: enforce zPCI state checking")
> >>>>>>>> Signed-off-by: Cornelia Huck <cohuck@redhat.com>  
> >>>>>>>
> >>>>>>> This patch does not change behaviour, so it is certainly not wrong.
> >>>>>>>
> >>>>>>> So lets have a look at if the bug report was actually a real bug or
> >>>>>>> just a missing annotation.
> >>>>>>>           
> >>>>>>>> ---
> >>>>>>>>     hw/s390x/s390-pci-inst.c | 2 ++
> >>>>>>>>     1 file changed, 2 insertions(+)
> >>>>>>>>
> >>>>>>>> diff --git a/hw/s390x/s390-pci-inst.c b/hw/s390x/s390-pci-inst.c
> >>>>>>>> index 61f30b8e55d2..00235148bed7 100644
> >>>>>>>> --- a/hw/s390x/s390-pci-inst.c
> >>>>>>>> +++ b/hw/s390x/s390-pci-inst.c
> >>>>>>>> @@ -1209,8 +1209,10 @@ int stpcifc_service_call(S390CPU *cpu, uint8_t r1, uint64_t fiba, uint8_t ar,
> >>>>>>>>          * FH Enabled bit is set to one in states of ENABLED, BLOCKED or ERROR. */
> >>>>>>>>         case ZPCI_FS_ERROR:
> >>>>>>>>             fib.fc |= 0x20;
> >>>>>>>> +        /* fallthrough */  
> >>>>>>>
> >>>>>>> This is correct, in case of an error we are also blocked.
> >>>>>>>           
> >>>>>>
> >>>>>> Agreed. This is definitely correct based on our architecture.
> >>>>>>         
> >>>>>>>>         case ZPCI_FS_BLOCKED:
> >>>>>>>>             fib.fc |= 0x40;
> >>>>>>>> +        /* fallthrough */  
> >>>>>>>
> >>>>>>> I think this is also correct, but  it would be good if Collin could verify.
> >>>>>>>           
> >>>>>>
> >>>>>> I failed to find anything to support setting the function control
> >>>>>> enabled bit when the function state is in error / blocked. I'm
> >>>>>> assuming this might be some QEMU hack to get things working? I'll have
> >>>>>> to dive further to understand why this was done this way, as it doesn't
> >>>>>> align with how the s390x architecture is documented. It's confusing.  
> >>>>>
> >>>>> Might this also be a real issue? Not matching the architecture is not a
> >>>>> good sign...  
> >>>>
> >>>> Friendly ping. If we still want to have this patch or a fix in 4.1, we
> >>>> need to find out soon...
> >>>>      
> >>>
> >>> Let's take it for now.
> >>>
> >>> Acked-by: Collin Walling <walling@linux.ibm.com>
> >>>  
> >>
> >> Just to be clear: You think that the current code is correct AFAYCS?  
> >   
> > I also looked into this again.
> > There is a possibility to also be in disabled state.
> >  From what I can see, it makes sense that blocked and error belong to the enable state
> > so the patch seems correct.
> >   
> 
> Yes I agree. The material I referenced required me to look over a few
> times and ask around a bit. The patch is good. Apologies for my
> ambiguous response.
> 

Ok, thanks for the clarification. Queued now.