Re: [Qemu-devel] [PATCH v3 1/7] s390x/pci: factor out endianess conversion

[Thomas Huth <thuth@redhat.com>]

On 23.11.2017 10:49, Cornelia Huck wrote:
> On Thu, 23 Nov 2017 09:48:41 +0100
> Thomas Huth <thuth@redhat.com> wrote:
> 
>> On 22.11.2017 23:05, Pierre Morel wrote:
>>> There are two places where the same endianness conversion
>>> is done.
>>> Let's factor this out into a static function.
>>>
>>> Signed-off-by: Pierre Morel <pmorel@linux.vnet.ibm.com>
>>> Reviewed-by: Yi Min Zhao <zyimin@linux.vnet.ibm.com>
>>> ---
>>>  hw/s390x/s390-pci-inst.c | 59 +++++++++++++++++++++++++++---------------------
>>>  1 file changed, 33 insertions(+), 26 deletions(-)
>>>
>>> diff --git a/hw/s390x/s390-pci-inst.c b/hw/s390x/s390-pci-inst.c
>>> index 8e088f3..3e1f1a0 100644
>>> --- a/hw/s390x/s390-pci-inst.c
>>> +++ b/hw/s390x/s390-pci-inst.c
>>> @@ -314,6 +314,36 @@ out:
>>>      return 0;
>>>  }
>>>  
>>> +/**
>>> + * Swap data contained in s390x big endian registers to little endian
>>> + * PCI bars.
>>> + *
>>> + * @ptr: a pointer to a uint64_t data field
>>> + * @len: the length of the valid data, must be 1,2,4 or 8
>>> + */
>>> +static int zpci_endian_swap(uint64_t *ptr, uint8_t len)
>>> +{
>>> +    uint64_t data = *ptr;
>>> +
>>> +    switch (len) {
>>> +    case 1:
>>> +        break;
>>> +    case 2:
>>> +        data = bswap16(data);
>>> +        break;
>>> +    case 4:
>>> +        data = bswap32(data);
>>> +        break;
>>> +    case 8:
>>> +        data = bswap64(data);
>>> +        break;
>>> +    default:
>>> +        return -EINVAL;
>>> +    }
>>> +    *ptr = data;
>>> +    return 0;
>>> +}  
>>
>> While you're at it, I think that should rather be leXX_to_cpu() instead
>> of bswapXX() here,
> 
> I don't think that's correct, as this is supposed to swap BE registers
> to LE PCI bars.

Yes, but for the CPU emulation, the registers are stored in the host's
endianness in the CPUS390XState structure. Or why do we byte-swap them
again with cpu_to_be64() during s390_store_status(), for example?

 Thomas