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

[Collin Walling <walling@linux.ibm.com>]

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.