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

From: Shannon Zhao <shannon.zhao@linaro.org>
To: Parth Dixit <parth.dixit@linaro.org>
Cc: keir@xen.org, Ian Campbell <ian.campbell@citrix.com>,
	andrew.cooper3@citrix.com, tim@xen.org,
	xen-devel <xen-devel@lists.xen.org>,
	Julien Grall <julien.grall@citrix.com>,
	Stefano Stabellini <stefano.stabellini@citrix.com>,
	Jan Beulich <jbeulich@suse.com>,
	Christoffer Dall <christoffer.dall@linaro.org>
Subject: Re: [PATCH v2 32/41] arm : acpi dynamically map mmio regions
Date: Fri, 31 Jul 2015 09:15:14 +0800	[thread overview]
Message-ID: <55BACC22.4050905@linaro.org> (raw)
In-Reply-To: <CABy3MN=otnyOU5=31Zg08FcRfLF=_9FxTsh+2vJ1Szr4FbYdOg@mail.gmail.com>


On 2015/7/31 2:02, Parth Dixit wrote:
> Hi Shannon,
>                     instead of getting mmio information for individual
> devices from dsdt, we will map all the non-ram regions described in
> uefi. 
Yes, I don't want to use AML interpreter either. But how to get all the
non-ram regions?

> 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@linaro.org> wrote:
>>
>>
>> On 2015/7/5 21:30, Parth Dixit wrote:
>>> +shannon
>>>
>>> On 15 June 2015 at 06:49, Julien Grall <julien.grall@citrix.com> wrote:
>>>> Hi Parth,
>>>>
>>>> On 14/06/2015 11:27, Parth Dixit wrote:
>>>>>
>>>>> On 8 June 2015 at 22:20, Julien Grall <julien.grall@citrix.com> 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

-- 
Shannon