linux-kernel - Re: [PATCH 1/4] ARM: STi: add stid127 soc support

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Date:	Wed, 5 Feb 2014 11:48:24 +0000
From:	srinivas kandagatla <srinivas.kandagatla@...com>
To:	Arnd Bergmann <arnd@...db.de>
Cc:	<linux-arm-kernel@...ts.infradead.org>,
	<devicetree@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>, <kernel@...inux.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	Patrice CHOTARD <patrice.chotard@...com>,
	<linux-kernel@...r.kernel.org>,
	Stuart Menefy <stuart.menefy@...com>,
	Rob Herring <robh+dt@...nel.org>,
	Grant Likely <grant.likely@...aro.org>,
	Giuseppe Cavallaro <peppe.cavallaro@...com>,
	<maxime.coquelin@...com>, <alexandre.torgue@...com>
Subject: Re: [PATCH 1/4] ARM: STi: add stid127 soc support

Hi Arnd,
On 31/01/14 20:15, Arnd Bergmann wrote:
> On Friday 31 January 2014, srinivas kandagatla wrote:
> 
>>> Sorry if I missed the initial review, but can you explain
>>> why this is needed to start with?
>>
>> On ST SoCs the default value for L2 AUX_CTRL register is 0x0, so we  set
>> the way-size explicit here.
> 
> Unfortunately, we keep going back and forth on the L2 cache controller
> setup between "it should work automatically" and "we don't want to
> have configuration data in DT", where my personal opinion is that
> the first one is more important here.
> 
> Now, there are a couple of properties that are defined in
> Documentation/devicetree/bindings/arm/l2cc.txt to let some of the
> things get set up automatically already. Can you check which bits
> are missing there, if any? Are they better described as "configuration"
> or "hardware" settings?

Currently l2cc bindings has few optional properties like.

- arm,data-latency
- arm,tag-latency
- arm,dirty-latency
- arm,filter-ranges
- interrupts :
- cache-id-part:
- wt-override:

These does not include properties to set "way-size", "associativity",
"enabling prefetching", "Prefetch drop enable", "prefetch offset",
"Double linefill" and few more in prefect control register and
aux-control register.

This is not just a issue with STi SOCs, having a quick look, I can see
that few more SOCs have similar requirements to set these properties.

We could do two things to get l2 setup automatically on STi SOCS.

1> Either define these properties case-by-case basic, which might be
useful for other SOCs too.

2> Or Add new compatible string for STi SoCs so that they can
automatically setup these values in cache-l2x0.c

Am Ok with either approaches.


Thanks,
srini


> 
> 	Arnd
> 
> 

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