[PATCH v4 4/4] ARM: BCM5301X: workaround suppress fault

[arnd@arndb.de (Arnd Bergmann)]

On Sunday 05 January 2014, Hauke Mehrtens wrote:
> Without this patch I am getting a unhandled fault exception like this
> one after "Freeing unused kernel memory":
> 
> Freeing unused kernel memory: 1260K (c02c1000 - c03fc000)
> Unhandled fault: imprecise external abort (0x1c06) at 0xb6f89005
> Kernel panic - not syncing: Attempted to kill init! exitcode=0x00000007
> 
> The address which is here 0xb6f89005 changes from boot to boot, with a
> new build the changes are bigger. With kernel 3.10 I have also seen
> this fault at different places in the boot process, but starting with
> 3.11 they are always occurring after the "Freeing unused kernel memory"
> message. I never was able to completely boot to userspace without this
> handler. The abort code is constant 0x1c06. This fault just happens
> once in the boot process I have never seen it happing twice or more.

How about narrowing down the abort handler to only ignore a single
fault after boot, and only with the abort code 0x1c06? That way you
don't risk silent data corruption in case something else goes wrong
after booting.

> This workaround was copied from the vendor code including most of the
> comments. It says it they think this is caused by the CFE boot loader
> used on this device. I do not have any access to any datasheet or
> errata document to check this.

Does the SoC by chance have a PCI host controller? The only other
platforms with this kind of handler have it to catch things going wrong
with PCI. Maybe another thing to try is to turn off the PCI core
at early boot.

	Arnd