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

[Julien Grall <julien.grall@xxxxxxx>]

Hi Stefano,

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.

Cheers,

--
Julien Grall

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