[U-Boot] [PATCH 1/1] efi_loader: remove efi_exit_caches()

[Tom Rini]

On Mon, Jul 22, 2019 at 08:51:41PM +0200, Heinrich Schuchardt wrote:
> On 7/22/19 3:36 PM, Tom Rini wrote:
> >On Sun, Jul 21, 2019 at 10:46:24AM +0100, Peter Robinson wrote:
> >>>>>>On Fri, Jul 19, 2019 at 7:28 PM Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
> >>>>>>>
> >>>>>>>In GRUB before 2.04 a bug existed which did not allow booting some ARM32
> >>>>>>>boards if U-Boot did not disable caches, cf.
> >>>>>>>https://lists.linaro.org/pipermail/cross-distro/2019-July/000933.html
> >>>>>>>
> >>>>>>>In ExitBootServices() we were disabling the caches by calling
> >>>>>>>cleanup_before_linux(). This workaround is not needed anymore.
> >>>>>>
> >>>>>>Do we want to remove this straight away? A lot of distributions will
> >>>>>>take time to move to grub 2.04 because it's been a long time between
> >>>>>>grub releases so they'll have quite a patch delta to re-align to the
> >>>>>>new release. Fedora for example will rebase to grub 2.04 in Fedora 32
> >>>>>>which will start development end of August but won't be released until
> >>>>>>next year.
> >>>>>
> >>>>>As described below this code does not remove any functionality that was
> >>>>>active in U-Boot v2019.04 or v2019.07.
> >>>>>
> >>>>>I can see nothing in https://fedoraproject.org/wiki/Updates_Policy
> >>>>>stopping GRUB 2.04 from being made available for stable Fedora releases.
> >>>>
> >>>>The maintainers believe that it's too intrusive to land now and they
> >>>>want maximum testing time before it gets to stable users, funnily
> >>>>enough people don't like it when their machines cease to boot.
> >>>
> >>>Why should anybody's machines cease to boot?
> >>>
> >>>If Fedora does not role out a new U-Boot they are fine. If Fedora roles
> >>>out a new U-Boot they should role out a matching GRUB and they are fine too.
> >>>
> >>>The venturous who build their own U-Boot should know how to role back
> >>>their system if needed.
> >>
> >>You've clearly never maintained a distribution across 1000s of device
> >>types and 100s of thousands of users.
> >>
> >>We will be shipping Fedora 31 with U-Boot 2019.10 and the current
> >>version of grub that the maintainers wish to support, if that requires
> >>me to revert a number of your changes I will, which will be an
> >>inconvenience and probably take more time than I have spare but I will
> >>survive. I find it strange you fix one OS only to break another. How
> >>will this work for users that want to boot a newly released device
> >>which has recently added U-Boot support to an already released stable
> >>OS?
> >>
> >>If you wish to actively break currently working use cases that's your
> >>prerogative that is your choice but I find breaking currently working
> >>use cases without a reasonable window to migrate dependencies actively
> >>hostile which has tended to not be the way U-Boot has worked in the
> >>past for such things as DM, so breaking a interface to the way OSes
> >>boot IMO is even worse.
> >
> >OK, we have a problem here.  A better example than DM would be the
> >various work-arounds we have (or carried for ages) to allow using newer
> >U-Boot with various old and broken kernels.  So no, we need to keep this
> >work-around for a long while.  What's the EOL date for any Linux
> >distribution that uses this broken grub?  The first U-Boot release post
> >that EOL date is when we can drop this particular bit of work-around
> >code.
> 
> The current behavior contradicts the UEFI spec. Our target is to
> implement a UEFI compliant firmware.

Our target is to be both compliant and functional, and functional wins.

> If OpenBSD does not change their broken boot loader will we never
> correct U-Boot? That would not make sense to me.

I'm sorry, I don't see the connection.  It's not "GRUB won't change to
be compliant" it's "GRUB changed things but it's going to take a long
while for that to be deployed out".

> Old distros tend not to to update their U-Boot release. E.g. Debian
> Stretch is still on U-Boot v2016.11. So why would you care about its EOL?

Because I want to make it really hard for people to end up in a "does
not boot now" mode.

> I could agree if you suggested that we should re-enable the workaround
> until the major distros use a compatible GRUB in their stable release
> like Debian Buster does.
> 
> Let's be proactive and analyze if anything is missing in Fedora Rawhide
> GRUB. If yes, we should contact the maintainer and clarify which
> adjustments are possible until the Fedora 31 release.

I don't want it to be "just latest stable has it".  I want it to be
"supported releases have it".

Why?  It's the user-friendly behavior.  You will find people that
upgrade their U-Boot because they're trying something but still have an
older distro.  Or people that are bringing up a new board and testing it
out with an older distro.

-- 
Tom
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