[U-Boot] [PATCH] arm: rmobile: bugfix: wrong register saving in lowlevel_init

[Albert ARIBAUD]

Hi Albert,

On Sun, 7 Oct 2012 19:19:37 +0200, Albert ARIBAUD
<albert.u.boot at aribaud.net> wrote:

> Hi Jeroen,
> 
> On Sun, 07 Oct 2012 17:18:27 +0200, Jeroen Hofstee
> <dasuboot at myspectrum.nl> wrote:
> 
> > Hello All,
> > 
> > On 10/07/2012 01:34 PM, Enric Balletbò i Serra wrote:
> > > Hi Albert,
> > >
> > > 2012/10/5 Albert ARIBAUD <albert.u.boot at aribaud.net>:
> > >> Hi Tetsuyuki,
> > >>
> > >> On Fri,  5 Oct 2012 13:39:22 +0900, Tetsuyuki Kobayashi
> > >> <koba at kmckk.co.jp> wrote:
> > >>
> > >>> lowlevel_init() of rmobile badly assumed that ip register holds return address.
> > >>> The commit "63ee53a7 armv7 cpu_init_crit: Simplify code" breaks this assumption.
> > >>> This patch removes this bad assumption and simplify code.
> > >>>
> > >>> Signed-off-by: Tetsuyuki Kobayashi <koba at kmckk.co.jp>
> > >>> ---
> > >>>
> > >> ...
> > > Note that the patch that Tetsuyuki says also breaks SPL support for
> > > OMAP3 boards, at least my IGEP boards doesn't boot and hangs at SPL
> > > level.
> > >
> > >    U-Boot SPL 2012.10-rc1-00244-g28e5ac2 (Oct 07 2012 - 13:11:29)
> > >
> > > Bisecting the problem I encountered the problem is the commit
> > > "63ee53a7 armv7 cpu_init_crit: Simplify code".
> > >
> > > Cheers,
> > >      Enric
> > >
> > I can confirm above. Also the tam3517 som (omap3) fails to boot due to
> > mentioned commit. The patch from Tetsuyuki is arch specific (rmobile) so
> > that won't fix the omap case. Reverting the patch, 63ee53a, does help.
> > 
> > Is there anything against reverting the patch (at least for the release...)?
> 
> Here is my opinion:
> 
> 1) I think patch 63ee53a7 is right in considering there is no need for
> cpu_init_crit to save lr in ip before calling lowlevel_init especially
> considering this is a tail call.
> 
> Only lowlevel_init can tell if it uses ip or lr for its own purposes,
> thus any saving of ip and/or lr due to the workings of lowlevel_init
> should be performed in lowlevel_init.
> 
> 2) I am not sure that the patch in this discussion depends on 63ee53a7,
> because IIUC, the patch simply saves ip "on a stack" then lr into ip,
> and after running s_init, restores from ip and ip from the stack; it
> never assumes ip contains a return address.
> 
> I know we're that close to the release, but I want to be sure we
> understand what needs fixing. Kobayashi, Jeroen, can you indicate
> precisely how the issues you encounter are related to 63ee53a7?

(adding back Tetsuyuki's mail in the Cc: list -- why had it
disappeared?)

> > Regards,
> > Jeroen
> 
> Amicalement,

Amicalement,
-- 
Albert.