Re: [Qemu-arm] [Qemu-devel] [RFC 0/2] ARM virt: Support up to 256 PCIe buses

[Laszlo Ersek]

On 05/24/18 11:11, Peter Maydell wrote:
> On 23 May 2018 at 21:52, Laszlo Ersek <address@hidden> wrote:
>> On 05/23/18 22:40, Auger Eric wrote:
>>> On 05/23/2018 07:45 PM, Laszlo Ersek wrote:
>>
>>>> Regarding the second patch, I do believe we need "more sophistication"
>>>> there. For example, I guess it could be possible to distinguish "-cpu
>>>> cortex-a15" from "-cpu cortex-a57" somehow, and stick with the low/small
>>>> ECAM in the former case. (The 32-bit firmware already runs on cortex-a15
>>>> only, and not on cortex-a57, according to my testing.)
>>>
>>> So we should detect we are in ACPI boot  + aarch32 mode to force legacy
>>> ECAM region, right?
>>
>> Agree about the aarch32 subcondition.
>>
>> However, "ACPI vs. DT" is not the right "other" subcondition here;
>> instead we should (minimally) check "firmware vs. no firmware". See the
>> "firmware_loaded" boolean field.
> 
> Won't it also break a guest which is just Linux loaded not via
> firmware which is an aarch32 kernel without LPAE support?

Does such a thing exist? (I honestly have no clue.)

If it does, then there are two options:
- don't enable the new ECAM range by default (always take an explicit
option),
- offer both ECAM ranges and let the guest pick one (I should add that I
have no idea whether exposing such *alternatives* is possible via DT and
ACPI; i.e., "pick one but not both").

Thanks
Laszlo