[PATCH RFC 2/2] ARM: nommu: remap exception base address to RAM
afzal.mohd.ma at gmail.com
Mon Jan 16 04:34:24 PST 2017
On Mon, Jan 16, 2017 at 09:53:41AM +0000, Vladimir Murzin wrote:
> On 15/01/17 11:47, Afzal Mohammed wrote:
> > mpu_setup_region() in arch/arm/mm/nommu.c that takes care of
> > MPU_RAM_REGION only. And that seems to be a kind of redundant as it is
> > also done in asm at __setup_mpu(). Git blames asm & C to consecutive
> > commits, that makes me a little shaky about the conclusion on it being
> > redundant.
> It is not redundant. MPU setup is done it two steps. The first step done in
> asm to enable caches, there only kernel image is covered; the second step takes
> care on the whole RAM given via dt or "mem=" parameter.
Okay, thanks for the details.
> > Thinking of invoking mpu_setup() from secondary_start_kernel() in
> > arch/arm/kernel/smp.c, with mpu_setup() being slightly modified to
> > avoid storing region details again when invoked by secondary cpu's.
> I have wip patches on reworking MPU setup code. The idea is to start using
> mpu_rgn_info actively, so asm part for secondariness would just sync-up
> content of that array. Additionally, it seems that we can reuse free MPU slots
> to cover memory which is discarded due to MPU alignment restrictions...
> > Vladimir, once changes are done after a revisit, i would need your
> > help to test on Cortex-R.
> I'm more than happy to help, but currently I have limited bandwidth, so if it
> can wait till the next dev cycle I'd try to make MPU rework finished by that
Okay, please feel free to do MPU rework the way you were planning, you
know more details & have the platform to achieve it with much higher
efficiency than me.
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