linux-kernel - Re: [PATCH] arm64: defconfig: enable EFI_ARMSTUB_DTB

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Date:   Wed, 5 Sep 2018 11:04:36 -0700
From:   Scott Branden <scott.branden@...adcom.com>
To:     Grant Likely <grant.likely@...retlab.ca>
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>,
        Olof Johansson <olof@...om.net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>,
        bcm-kernel-feedback-list@...adcom.com,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Leif Lindholm <leif.lindholm@...aro.org>,
        Alexander Graf <agraf@...e.de>
Subject: Re: [PATCH] arm64: defconfig: enable EFI_ARMSTUB_DTB_LOADER



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.
>
> g.
>
> g.
Thanks,
  Scott