l2c: Kernel panic in l2c310_enable() in non-secure mode

[slash.tmp@free.fr (Mason)]

On 14/10/2015 19:47, Russell King - ARM Linux wrote:
> On Wed, Oct 14, 2015 at 04:47:59PM +0200, Marc Gonzalez wrote:
>> Just to be sure, I changed set_auxcr() to a NOP. The kernel does not
>> panic with that setup, and I can see the boot messages:
>>
>> [    0.000000] l2x0_of_init: FOO
>> [    0.000000] L2C-310 enabling early BRESP for Cortex-A9
>> [    0.000000] L2C-310: enabling full line of zeros but not enabled in Cortex-A9
>> [    0.000000] reg=0x104 val=0x66460801
>> [    0.000000] reg=0x100 val=0x1
>> [    0.000000] L2C-310 I prefetch enabled, offset 1 lines
>> [    0.000000] L2C-310 dynamic clock gating enabled, standby mode enabled
>> [    0.000000] L2C-310 cache controller enabled, 8 ways, 512 kB
>> [    0.000000] L2C-310: CACHE_ID 0x410000c8, AUX_CTRL 0x62460801
>>
>> The "reg=0x%x val=0x%lx\n" lines are from tango_l2c_write_sec()
>>
>> It seems the firmware forgot to enable FLOZ.
> 
> Wrong.  Do _not_ enable FLZ in the Cortex-A9.  FLZ needs the L2 cache
> enabled _before_ the Cortex A9.  This is not something you can do in
> firmware/boot loader/etc.  It has to be done by the kernel when the L2
> cache is initialised.
> 
> If your firmware prevents this, sorry, you can't ever use FLZ.

Is FLZ just a performance optimization?

I can ask the firmware author not to enable bit 0 in L2CC AUXCTRL.

Then Linux won't try to write CP15 ACTRL, IIUC.

Regards.