[PATCH] ARM: imx6: allow booting with old DT

[l.stach@pengutronix.de (Lucas Stach)]

Am Mittwoch, den 27.05.2015, 15:34 +0800 schrieb Shawn Guo:
> On Tue, May 26, 2015 at 06:43:36PM +0200, Lucas Stach wrote:
> > The GPC rewrite to IRQ domains has been on the premise that it may break
> > suspend/resume for new kernels on old DT, but otherwise keep things working
> > from a user perspective. This was an accepted compromise to be able to move
> > the GIC cleanup forward.
> > 
> > What actually happened was that booting a new kernel on an old DT crashes
> > before even the console is up, so the user does not even see the warning
> > that the DT is too old. The warning message suggests that this has been
> > known before, which is clearly unacceptable.
> 
> To see any early message like this one, low-level debug support is
> expected to be turned on.
> 
Using low-level debug might be acceptable for a developer.

>From a user perspective a kernel update without a corresponding DT
update should never render the machine completely broken. Keep in mind
that i.MX6 isn't only used in deeply embedded system, but is already in
devices where non-developer users might update the kernel. They might
even use prebuilt kernels where enabling low-level debug is not an
option.
We are not free to break the existing DT stability rules in such a
drastic way, especially if keeping things working to some extent is
easily done.

I have another patch to fix a power domain problem with new kernel on
old DT. Will send out in a minute.

Regards,
Lucas

> But anyway, with your change, we get a much better situation.  Will send
> it to arm-soc soon.  Thanks for the patch.
> 
> Shawn
> 
> > 
> > Fix the early crash by mapping the GPC memory space if the IRQ controller
> > doesn't claim it. This keeps at least CPUidle and the needed CPU wakeup
> > workarounds working. With this fixed the system is able to boot up
> > properly minus the expected suspend/resume breakage.
> > 
> > Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
> > ---
> > Shawn, this is a critical fix for 4.1, to keep the combination of old
> > DT + new kernel at least somewhat working, to allow users to resolve
> > the situation on their systems. Please make sure this gets forwarded
> > ASAP.
> > ---
> >  arch/arm/mach-imx/gpc.c | 12 +++++++++---
> >  1 file changed, 9 insertions(+), 3 deletions(-)
> > 
> > diff --git a/arch/arm/mach-imx/gpc.c b/arch/arm/mach-imx/gpc.c
> > index 4d60005e9277..bbf015056221 100644
> > --- a/arch/arm/mach-imx/gpc.c
> > +++ b/arch/arm/mach-imx/gpc.c
> > @@ -280,9 +280,15 @@ void __init imx_gpc_check_dt(void)
> >  	struct device_node *np;
> >  
> >  	np = of_find_compatible_node(NULL, NULL, "fsl,imx6q-gpc");
> > -	if (WARN_ON(!np ||
> > -		    !of_find_property(np, "interrupt-controller", NULL)))
> > -		pr_warn("Outdated DT detected, system is about to crash!!!\n");
> > +	if (WARN_ON(!np))
> > +		return;
> > +
> > +	if (WARN_ON(!of_find_property(np, "interrupt-controller", NULL))) {
> > +		pr_warn("Outdated DT detected, suspend/resume will NOT work\n");
> > +
> > +		/* map GPC, so that at least CPUidle and WARs keep working */
> > +		gpc_base = of_iomap(np, 0);
> > +	}
> >  }
> >  
> >  #ifdef CONFIG_PM_GENERIC_DOMAINS
> > -- 
> > 2.1.4
> > 

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