Re: [Xen-devel] [PATCH v2 32/41] arm : acpi dynamically map mmio regions

[Parth Dixit <parth.dixit@xxxxxxxxxx>]

Hi Shannon,
                    instead of getting mmio information for individual
devices from dsdt, we will map all the non-ram regions described in
uefi. AML interpreter option was discussed earlier and it was decided
not to go with that approach. You can find more details in the linaro
xen wiki for the reasoning behind it.

regards
parth

On 30 July 2015 at 17:49, Shannon Zhao <shannon.zhao@xxxxxxxxxx> wrote:
>
>
> On 2015/7/5 21:30, Parth Dixit wrote:
>> +shannon
>>
>> On 15 June 2015 at 06:49, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
>>> Hi Parth,
>>>
>>> On 14/06/2015 11:27, Parth Dixit wrote:
>>>>
>>>> On 8 June 2015 at 22:20, Julien Grall <julien.grall@xxxxxxxxxx> wrote:
>>>>>
>>>>> Hi Parth,
>>>>>
>>>>> On 17/05/2015 21:03, Parth Dixit wrote:
>>>>>>
>>>>>>
>>>>>> In ACPI mmio regions are described in DSDT which requires
>>>>>> AML interpreter. Defer the mapping of mmio until DSDT is parsed in
>>>>>> DOM0 and map mmio's dynamically at the time of request.
>>>>>
>>>>>
>>>>>
>>>>> I'm against a such solution. Even though it's DOM0 we should avoid to
>>>>> allow
>>>>> him to map anything (RAM,...) on data abort.
>>>>
>>>> I think we agreed to this solution
>>>> http://lists.xenproject.org/archives/html/xen-devel/2015-06/msg02059.html
>>>
>>>
>>> Firstly, this kind of link should have been put in the changelog of the
>>> patch (after ---). It helps the reviewer to know what was decided (or not)
>>> on the previous discussion. It's more true with a series of more than 40
>>> patches...
>>>
>>> Secondly, the thread you pointed as some discussion on it but no formal
>>> agreement about what to do. If there is no answer, it's better to do a
>>> resume and ask if anyone are agree.
>>>
>>> Finally, what you've implemented and what was suggested by Ian is different.
>>> You are allowing any region to be mapped in DOM0 via this way. Only MMIO
>>> should be allowed.
>>>
>>> Concerning the mapping attribute used. Based on Ard answer "The UEFI spec
>>> mandates that the memory map describes all memory in the system, so if dom0
>>> accesses any ranges outside of that, it makes sense
>>> to just use device mappings for stage 2.". We should use by default Device
>>> Stage 2, it's safer. If it doesn't work later (because some PCI BAR may be
>>> memory, which if I wasn't able to prove), then we can think differently.
>>>
>>> For the mapping of the MMIO to DOM0, I believe we can map any non-RAM (and
>>> any non-RAM not used by Xen) regions to DOM0 at boot time (I think x86 does
>>> that). It would keep the ACPI code contained at boot time and no difference
>>> during runtime.
>>>
>
> But How do we get the MMIO information of the devices in DSDT table? If
> we want to parse DSDT table, we must introduce AML interpreter, IIUC.
>
> Julien, do you have any other ideas?
>
> Thanks,
> --
> Shannon

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