[U-Boot] [PATCH 05/12] sunxi: Move setting of CPU system control register SMP bit to save_boot_params

[Albert ARIBAUD]

Hello Hans,

On Mon, 19 Jan 2015 20:04:58 +0100, Hans de Goede <hdegoede at redhat.com>
wrote:
> Hi,
> 
> On 17-01-15 23:51, Ian Campbell wrote:
> > On Thu, 2015-01-15 at 15:52 +0100, Hans de Goede wrote:
> >> According to the "Cortex-A7 MPCore Technical Reference Manual":
> >>
> >> "You must ensure this bit is set to 1 before the caches and MMU are enabled,
> >> or any cache and TLB maintenance operations are performed."
> >
> > Given that this is a feature of the Cortex-A7 (actually, I believe it
> > applies to at least Cortex-A15 too) and not really specific to sunxi,
> > perhaps we can make this more generic?
> 
> Strange enough the bit is different between the A7 and A15, for the A7 the docs
> say it must be set before doing anything with caches, on the A15 it only needs
> to be set for the core to accept cache management operations from other cpu
> cores (or so the docs say), which is likely why it is not in the standard
> init sequence yet, as for u-boot it seems to only be necessary to do this on
> a Cortex A7. I agree that it would be good to move this to the generic start.S
> though, Albert ?

[...]

> >> Since arch/arm/cpu/armv7/start.S: cpu_init_cp15 does several cache operations,
> >> we should thus enable the SMP bit earlier, and the only chance to do that is
> >> to do it at save_boot_params time.
> >
> > Would it be so terrible to add an ifdef CORTEX_A7 here, or to call out
> > to (or call as a macro) a soc_init_cp15?
> 
>  From my pov no that would not be too terrible, but ...
> >
> > I'm cc-ing Albert for input these questions.
> 
> That indeed is Albert's call.

Will look into this today.

Amicalement,
-- 
Albert.