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



Hi Stefano,

On 20/02/17 18:13, Julien Grall wrote:
On 20/02/17 18:12, Stefano Stabellini wrote:
On Mon, 20 Feb 2017, Julien Grall wrote:
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@xxxxxxx>

---
    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.

All right, but in this case you need to update
docs/misc/xen-command-line.markdown.

Sure, I will do it in the next version.

Actually, I will defer this patch a bit and resend the rest of the series.

Cheers,

--
Julien Grall

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