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

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

On 7/16/19 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>