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Date: Sun, 9 Sep 2018 17:55:55 +0200
From: Ard Biesheuvel <ard.biesheuvel@...aro.org>
To: Catalin Marinas <catalin.marinas@....com>
Cc: Scott Branden <scott.branden@...adcom.com>,
Grant Likely <grant.likely@...retlab.ca>,
Arnd Bergmann <arnd@...db.de>,
Will Deacon <will.deacon@....com>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
Leif Lindholm <leif.lindholm@...aro.org>,
Alexander Graf <agraf@...e.de>,
BCM Kernel Feedback <bcm-kernel-feedback-list@...adcom.com>,
Olof Johansson <olof@...om.net>,
Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] arm64: defconfig: enable EFI_ARMSTUB_DTB_LOADER
On 9 September 2018 at 13:07, Catalin Marinas <catalin.marinas@....com> wrote:
> On Wed, Sep 05, 2018 at 11:04:36AM -0700, Scott Branden wrote:
>> On 18-09-05 11:00 AM, Grant Likely wrote:
>> > On Wed, Sep 5, 2018 at 6:27 PM Scott Branden <scott.branden@...adcom.com> wrote:
>> > > On 18-09-05 02:40 AM, Ard Biesheuvel wrote:
>> > > > On 4 September 2018 at 19:19, Scott Branden <scott.branden@...adcom.com> wrote:
>> > > > > Rather than introduce EFI_ARMSTUB_DTB_LOADER, why not have
>> > > > > the efistub use CONFIG_OF to determine whether it supports dtb= or not?
>> > > > >
>> > > > > That way ACPI-only distros disable devicetree support entirely.
>> > > > >
>> > > > Unfortunately, CONFIG_OF cannot be disabled on arm64 even on ACPI-only builds.
>> > > OF shouldn't be automatically selected in the arm64/Kconfig. It should
>> > > have a config parmaeter like other archs as mips and arm. I can
>> > > submit a patch so it functions the same way as other archs so it
>> > > is not always selected. It will be good to add a USE_OF config
>> > > options like the other archs (or simply remove the select from the
>> > > Kconfig and choose OF directly in the defconfig. This will have
>> > > the added benefit of doing away with OF support when its not
>> > > needed on an ARM64 platform. ACPI is already not automatically
>> > > selected for all ARM64 platforms, nor should devicetree.
>> > We don't do that on Arm because a devicetree is always required at
>> > boot time. Even on ACPI systems a tiny DTB is used containing just a
>> > /chosen node for passing the kernel command line and the initrd
>> > location.
>>
>> Seems bizarre DTB is not needed for x86 to boot from UEFI with ACPI
>> support? I'll look into it further at some point in order to remove such
>> anomaly. There should be no need for such devicetree reliance.
>
> I'd say don't waste time on this, the patch would not get merged ;). As
> Grant said, we use a tiny dtb to pass the command line, initrd to the
> kernel. You'd have to invent an alternative (setup_header, ATAGs) and I
> really don't see the point of increased complexity just because of some
> philosophical arguments against OF.
>
Not just that: we also need of_match_table support for ACPI's PRP0001
device (which is a horrible hack in itself, but currently supported in
Linux/arm64 *and* Linux/x86 nonetheless)
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