Re: [PATCH 3/8] xen/arm: acpi: Don't fallback on DT when user request ACPI

[Julien Grall <julien.grall@arm.com>]

Hi Stefano,

On 02/16/2017 01:41 AM, Stefano Stabellini wrote:
> On Fri, 3 Feb 2017, Julien Grall wrote:
>> On ARM, when the user put 'acpi=force' Xen will use ACPI over DT.
>> Currently, if Xen fails to initialize ACPI it will fallback on DT.
>>
>> This behavior makes difficult for a user to notice Xen didn't used ACPI
>> has requested on platform where the firmware is providing both ACPI and DT.
>>
>> Rather than fallback on DT during a failure, panic when 'acpi=force'.
>>
>> Signed-off-by: Julien Grall <julien.grall@arm.com>
>>
>> ---
>>     I am wondering if we should do the same with acpi=on. So a user
>>     would notice directly if something went wrong with ACPI.
>>     Otherwise you would boot up to the prompt and barely notice that DT
>>     was used.
>
> I would keep the current behavior as is and add new parameter that means
> "acpi and only acpi". Today acpi=force means "acpi is preferred to
> device tree". It doesn't mean that if acpi fail, Xen should panic.
>
> Maybe acpi=strict or acpi=mandatory?

We have a bunch of option that makes little sense today:
    - off: Turned off ACPI
    - on: Turned on ACPI only if DT is empty
    - force: Turned on ACPI

If ACPI fails you fallback on DT. This is a pain to detect whether DT or 
ACPI is been used. So I think adding another option will only confuse 
the user.

Looking at Linux the option are:
     - off: Turned off ACPI
     - on: Prefer ACPI over DT. Fallback on DT is failed
     - force: Use ACPI and panic if not available

I would much prefer to use the behavior of the acpi param on Linux 
because it will avoid the user to be confused on the usage.

Cheers,

-- 
Julien Grall

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