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

[Rob Herring <robherring2@gmail.com>]

On 11/13/2013 06:41 PM, Tomasz Figa wrote:
> 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.

I believe SMP is enabled before any initcalls.

> 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.

Unfortunately, non-secure mode platforms like highbank and omap have to
make platform specific smc calls.

Rob