Re: [PATCH v6 2/3] xen/arm: Enable the existing x86 virtual PCI support for ARM.

[Jan Beulich <jbeulich@xxxxxxxx>]

On 15.10.2021 14:28, Bertrand Marquis wrote:
>> On 15 Oct 2021, at 13:18, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>> On 15.10.2021 14:13, Bertrand Marquis wrote:
>>>> On 15 Oct 2021, at 12:35, Roger Pau Monné <roger.pau@xxxxxxxxxx> wrote:
>>>> On Fri, Oct 15, 2021 at 12:18:59PM +0200, Jan Beulich wrote:
>>>>> On 15.10.2021 12:14, Ian Jackson wrote:
>>>>>> Bertrand Marquis writes ("Re: [PATCH v6 2/3] xen/arm: Enable the 
>>>>>> existing x86 virtual PCI support for ARM."):
>>>>>>>> On 15 Oct 2021, at 09:00, Jan Beulich <jbeulich@xxxxxxxx> wrote:
>>>>>>>> The latter is fine to be put here (i.e. FTAOD I'm fine with it
>>>>>>>> staying here). For the former I even question its original placement
>>>>>>>> in asm-x86/pci.h: It's not generally correct as per the PCI spec, as
>>>>>>>> the bus portion of the address can be anywhere from 1 to 8 bits. And
>>>>>>>> in fact there is a reason why this macro was/is used in only a
>>>>>>>> single place, but not e.g. in x86'es handling of physical MCFG. It
>>>>>>>> is merely an implementation choice in vPCI that the entire segment 0
>>>>>>>> has a linear address range covering all 256 buses. Hence I think
>>>>>>>> this wants to move to xen/vpci.h and then perhaps also be named
>>>>>>>> VPCI_ECAM_BDF().
>>>>>>>
>>>>>>> On previous version it was request to renamed this to ECAM and agreed
>>>>>>> to put is here. Now you want me to rename it to VPCI and move it again.
>>>>>>> I would like to have a confirmation that this is ok and the final move 
>>>>>>> if possible.
>>>>>>>
>>>>>>> @Roger can you confirm this is what is wanted ?
>>>>>>
>>>>>> I think Roger is not available today I'm afraid.
>>>>>>
>>>>>> Bertrand, can you give me a link to the comment from Roger ?
>>>>>> Assuming that it says what I think it will say:
>>>>>>
>>>>>> I think the best thing to do will be to leave the name as it was in
>>>>>> the most recent version of your series.  I don't think it makes sense
>>>>>> to block this patch over a naming disagreement.  And it would be best
>>>>>> to minimise unnecessary churn.
>>>>>>
>>>>>> I would be happy to release-ack a name change (perhaps proposed bo Jan
>>>>>> or Roger) supposing that that is the ultimate maintainer consensus.
>>>>>>
>>>>>> Jan, would that approach be OK with you ?
>>>>>
>>>>> Well, yes, if a subsequent name change is okay, then I could live with
>>>>> that. I'd still find it odd to rename a function immediately after it
>>>>> already got renamed. As expressed elsewhere, I suspect in his request
>>>>> Roger did not pay attention to a use of the function in non-ECAM code.
>>>>
>>>> Using MMCFG_BDF was original requested by Julien, not myself I think:
>>>>
>>>> https://lore.kernel.org/xen-devel/a868e1e7-8400-45df-6eaa-69f1e2c99383@xxxxxxx/
>>>>
>>>> I'm slightly loss in so many messages. On x86 we subtract the MCFG
>>>> start address from the passed one before getting the BDF, and then we
>>>> add the startting bus address passed in the ACPI table. This is so far
>>>> not need on Arm AFAICT because of the fixed nature of the selected
>>>> virtual ECAM region.
>>>
>>> At the end my patch will add in xen/pci.h:
>>> #define ECAM_BDF(addr)         (((addr) & 0x0ffff000) >> 12)
>>
>> Since you still make this proposal, once again: I'm not going to
>> accept such a macro in this header, whatever the name. Its prior
>> placement was wrong as well. Only ...
>>
>>> #define ECAM_REG_OFFSET(addr)  ((addr) & 0x00000fff)
>>
>> ... this one is fine to live here (and presumably it could gain uses
>> elsewhere).
> 
> So you would agree if they are both moved to vpci.h with a VPCI_ prefix ?

I wouldn't object, but as said several times before I see no reason
to also move and rename ECAM_REG_OFFSET(). If you moved it and if
later we find a use for it outside of vPCI, we'd need to rename and
move it again.

Jan