Re: [PATCH 1/1] ARM: EXYNOS: Initialize L2x0 cache controller for Exynos4 only

[Tomasz Figa <tomasz.figa@gmail.com>]

Hi Will,

On Friday 25 of October 2013 14:48:52 Will Deacon wrote:
> On Sat, Oct 19, 2013 at 03:04:22PM +0100, Tomasz Figa wrote:
> > On Saturday 19 of October 2013 18:09:15 Sachin Kamat wrote:
> > > Hi Tomasz,
> > > 
> > > On 17 October 2013 18:35, Tomasz Figa <t.figa@samsung.com> wrote:
> > > > Hi Sachin,
> > > > 
> > > > On Thursday 17 of October 2013 17:33:12 Sachin Kamat wrote:
> > > >> L2x0 cache controller is present only in Cortex-A9 based Exynos4 SoCs.
> > > >> Thus move this function to Exynos4 early init call to avoid non-Exynos4
> > > >> SoCs from calling this function in multi-platform support.
> > > > 
> > > > I believe that at the time .init_early() is called there is no ioremap()
> > > > infrastructure working yet and so L2 cache initialization which needs
> > > > it will cause a kernel panic. This patch worked only because currently
> > > > there is no L2X0 controller defined in device tree sources of Exynos 4.
> > > 
> > > It is not clear to me as to why device tree entry is required for this
> > > to work in current form
> > > as we call the  L2X0 init function explicitly.
> > 
> > L2x0 controller is just another IP block on the SoC. In addition its
> > registers are memory mapped and the driver needs some way to get their
> > location. The function being called explicitly simply scans device tree
> > for applicable node and performs rest of the setup only if it finds one.
> > 
> > Ideally there should be no need to call this function explicitly, as it
> > should be called by some code based on presence of applicable device tree
> > node.
> 
> It's a nice idea, but you need to be careful if you start deferring this
> stuff. Aside from the potential performance loss during early boot, I'm not
> even sure that the l2x0_init function is safe to run with IRQs enabled.
> 
> Will

I just realised that I have not replied to your message, sorry for that.

So, my intention was not deferring this, but rather making this more
generic. In case of Exynos, we call l2x0_of_init() from an early_initcall
which is long time already after enabling interrupts, but still before
SMP is initialized.

My idea was to create a generic early_initcall in arch/arm/mm/cache-l2x0.c
that would scan DT for applicable node, parse aux_val and aux_mask from
such node (if found) and then initialize L2X0 without any need for
having platform-specific code.

However my concern here is whether on some platforms such platform code
wouldn't be needed anyway. Unfortunately I don't really know enough
about L2X0 to be able to answer this myself, at least at the moment.

Best regards,
Tomasz