[RFC 08/18] arm: msm: set L2CR1 to enable prefetch and burston Scorpion.

[Shilimkar, Santosh]

> -----Original Message-----
> From: linux-arm-kernel-bounces at lists.infradead.org [mailto:linux-arm-kernel-
> bounces at lists.infradead.org] On Behalf Of Catalin Marinas
> Sent: Tuesday, January 12, 2010 4:22 PM
> To: Russell King - ARM Linux
> Cc: Larry Bassel; Daniel Walker; linux-arm-kernel at lists.infradead.org
> Subject: Re: [RFC 08/18] arm: msm: set L2CR1 to enable prefetch and burston Scorpion.
> 
> On Mon, 2010-01-11 at 23:45 +0000, Russell King - ARM Linux wrote:
> > On Mon, Jan 11, 2010 at 02:47:27PM -0800, Daniel Walker wrote:
> > > From: Larry Bassel <lbassel at quicinc.com>
> > >
> > > This change improves the following LMBench benchmarks
> > > by over 15%:
> >
> > Is this something that could be done in the platform initialisation code
> > rather than the processor code?  It's clearly not specific to all ARMv7
> > CPUs.
> 
> We discussed in the past but the thread died. There are various bits
> that may need to be enabled before the CPU is initialised but it is
> highly dependent on the hardware configuration and not only the CPU
> type. For example, Cortex-A8/A9 may have some bits in the ACTLR register
> which are fine to set on RealView but not on OMAP because the kernel
> there is running in non-secure mode. Now Scorpion has other needs.
> 
> Since such initialisation would run before the MMU is enabled, should we
> add an additional per-platform macro to be invoked before the CPU is set
> up? A pointer in the machine_desc structure to an asm routine would also
> work assuming that care is taken to calculate the phys address and the
> code is position independent.
Thanks for bringing out this. A per-platform macro would be usefull and
easy to populate and surely needed one.
> An alternative would be to briefly enable the MMU for the initialisation
> (using a temporary page table) than disable it and switch to the proper
> one built via create_mapping(). This would allow some initialisation
> code to be written in C (though I'm not sure it's worth the effort).
> 

Regards,
Santosh