[Arm-dev] ACPI

Scott Branden scott.branden at broadcom.com
Fri Oct 13 23:17:07 UTC 2017

Hi Jon,

Could you point me at the ARM server standards you are referring to


-----Original Message-----
From: Arm-dev [mailto:arm-dev-bounces at centos.org] On Behalf Of Jon Masters
Sent: Thursday, October 12, 2017 6:57 PM
To: arm-dev at centos.org
Subject: [Arm-dev] ACPI

Hi all,

Most of you know me. For those who don't, I'm Chief ARM Architect at Red
Hat and started the internal Red Hat ARM team back in 2011. I've also
worked on creating most of the ARM server standards, and with every
silicon vendor since their design was a paper napkin drawing.

So it is with some authority I can tell you that ARM servers without ACPI
have no future. Those of you booting with "acpi=off" are running machines
completely in violation of the ARM server specs (which mandate the use of
ACPI tables). You can choose to do this, but such configs have never been
tested and are completely guaranteed to break randomly in the future when
you update the distribution, or the hardware.

But not everyone has fully gotten this message. Beginning in the next
release of the upstream distro from which CentOS inherits its sources,
there is a nasty warning message which will be printed if you boot while
attempting to disable ACPI, or even if the platform contains DeviceTree
tables (whether used or not). The kernel will also taint itself if it
detects the presence of DeviceTree on a platform at all.

Going forward, I am instituting logic that will cause the kernel to panic
and fail to boot at all when a platform contains a DeviceTree (whether
used or not) unless some parameter like "platform_is_broken" is passed to
the kernel. This is irrespective of whether you actually boot with ACPI or
not. All platforms that aren't simply ACPI must be removed from the face
of the earth as quickly as possible and replaced with fully standardized
ones compliant with the ARM server specs. The good news is that firmware
updates will allow anyone still shipping a DeviceTree to remove it from
future platform updates to be compliant.

Now is a good time to stop thinking about disabling ACPI. It is only going
to get much, much harder to turn it off.

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