RE: [PATCH][RFC,v4] ACPI / PM: Introduce efi poweroff for HW-full platforms without _S5

["Chen, Yu C" <yu.c.chen@intel.com>]

Hi Matt,

> -----Original Message-----
> From: Matt Fleming [mailto:matt@codeblueprint.co.uk]
> Sent: Friday, March 11, 2016 11:56 PM
> To: Chen, Yu C
> Cc: linux-acpi@vger.kernel.org; linux-pm@vger.kernel.org; Rafael J. Wysocki;
> Len Brown; Thomas Gleixner; Ingo Molnar; H. Peter Anvin; Zhang, Rui; linux-
> efi@vger.kernel.org; x86@kernel.org; linux-kernel@vger.kernel.org; Ard
> Biesheuvel; Mark Salter
> Subject: Re: [PATCH][RFC,v4] ACPI / PM: Introduce efi poweroff for HW-full
> platforms without _S5
> 
> On Fri, 11 Mar, at 05:05:33PM, Chen Yu wrote:
> > The problem is Linux registers pm_power_off = efi_power_off only if we
> > are in hardware reduced mode. Actually, what we also want is to do
> > this when ACPI S5 is simply not supported on non-legacy platforms.
> > That should handle both the HW reduced mode, and the HW-full mode
> > where the DSDT fails to supply an _S5 object.
> >
> > This patch introduces pm_power_off_default which would be used by
> > pm_power_off if nothing else is available. And in this case we
> > leverage efi power off to be this role. However since efi power off
> > may not be stable enough thus in order not to interfere with other
> > poweroff path, we only make a minimum enhancement for x86 in
> > native_machine_power_off.
> >
> > Suggested-by: Len Brown <len.brown@intel.com>
> > Signed-off-by: Chen Yu <yu.c.chen@intel.com>
> > ---
> > v4:
> >  - Since in v3 efi_poweroff_required() is not guaranteed to run
> >    after all of the other code that may register alternative
> >    power off handling, add the pm_power_off_default that would
> >    be used by pm_power_off if nothing else is available.
> > v3:
> >  - Only assign pm_power_off to efi_power_off when there are no
> >    other pm_power_off registered at that time, in case other
> >    commponents would like to customize their own implementation.
> > ---
> > v2:
> >  - Convert the acpi_no_s5 to a global bool variable in sleep.c and
> >    add a declaration to include/linux/acpi.h.
> > ---
> >  arch/x86/kernel/reboot.c       | 3 +++
> >  arch/x86/platform/efi/quirks.c | 5 +++++
> >  drivers/acpi/sleep.c           | 7 +++++++
> >  drivers/firmware/efi/reboot.c  | 8 ++++++++
> >  include/linux/acpi.h           | 1 +
> >  include/linux/efi.h            | 1 +
> >  include/linux/pm.h             | 1 +
> >  kernel/reboot.c                | 1 +
> >  8 files changed, 27 insertions(+)
> 
> Couple of things,
> 
>   1) I'm still waiting for an answer to my question on whether
>      platforms without _S5 that need EFI reset actually exist. You
>      said they "might" exist, which makes this all sound very
>      speculative. It is not obvious to me that this approach makes
>      sense.
There is  a future Base-IA platform, we are planning to skip
implementing the SLP_TYP register and the S5 object.  (already there
will be no S3 and no S4)

> 
>   2) In v4 you're modifying the generic EFI reboot code and should Cc
>      other developers who might care, e.g. the arm64 folks. I've Cc'd
>      them now.
OK, thanks.

yu