linux-kernel - Re: [PATCH] ARM: l2x0: add prefetch and power ctrl registers configuration support

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Message-ID: <20131107141643.GB4440@lunn.ch>
Date:	Thu, 7 Nov 2013 15:16:43 +0100
From:	Andrew Lunn <andrew@...n.ch>
To:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Cc:	Jisheng Zhang <jszhang@...vell.com>, rob.herring@...xeda.com,
	pawel.moll@....com, mark.rutland@....com, swarren@...dotorg.org,
	ijc+devicetree@...lion.org.uk, rob@...dley.net,
	linux@....linux.org.uk, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-doc@...r.kernel.org
Subject: Re: [PATCH] ARM: l2x0: add prefetch and power ctrl registers
 configuration support

On Thu, Nov 07, 2013 at 01:46:44PM +0100, Sebastian Hesselbarth wrote:
> On 11/07/13 06:07, Jisheng Zhang wrote:
> >PL310 supports Prefetch offset/control register from r2p0 and Power
> >control register from r3p0. This patch adds the support to configure
> >these two registers if there are. The dt binding document is also updated.
> >
> >Signed-off-by: Jisheng Zhang <jszhang@...vell.com>
> >---
> >  Documentation/devicetree/bindings/arm/l2cc.txt |  4 ++++
> >  arch/arm/mm/cache-l2x0.c                       | 19 +++++++++++++++++++
> >  2 files changed, 23 insertions(+)
> >
> >diff --git a/Documentation/devicetree/bindings/arm/l2cc.txt b/Documentation/devicetree/bindings/arm/l2cc.txt
> >index c0c7626..32cd08c 100644
> >--- a/Documentation/devicetree/bindings/arm/l2cc.txt
> >+++ b/Documentation/devicetree/bindings/arm/l2cc.txt
> >@@ -39,6 +39,10 @@ Optional properties:
> >  - arm,filter-ranges : <start length> Starting address and length of window to
> >    filter. Addresses in the filter window are directed to the M1 port. Other
> >    addresses will go to the M0 port.
> >+- arm,prefetch-ctrl : The value for Prefetch Offset/Control Register if there
> >+  is. This is a single cell.
> >+- arm,pwr-ctrl : The value for Power Control Register if there is. This is a
> >+  single cell.
> 
> Jisheng,
> 
> I did some research over L2x0/L310 aux-ctrl registers and possible
> properties for them. Both properties introduced here, just allow you
> to put in a magic number, while IMHO properties should better reflect
> the actual function rather than hard-coded values.
> 
> A quick look at L310 TRM for Power Control Register gives:
> 
> Bit 1: dynamic_clk_gating_en (1=enabled, 0=masked)
> Bit 0: standby mode en (1=enabled, 0=masked)
> 
> So, properties should one of:
> 
> (a) arm,dynamic-clock-gating = <0/1>
>     arm,standby-mode = <0/1>
> (b) arm,dynamic-clock-gating-enable/-disable;
>     arm,standby-mode-enable/-disable
> 
> If we want to have set/clear/don't touch behavior, I'd prefer (a) as
> it is easier to deal with in code. Moreover, -enable/-disable of (b)
> may not always fit the property name, so there will also be
> arm,no-feature-foo or arm,force-feature-bar.

Hi Sebastian

There have been some comments about properties with Boolean
values. Rather than having a Boolean, you simply don't list the
property.

What you have here is slightly different, since you have
set/clear/don't touch. How to represent this should be decided once by
the DT folks, and used consistently in all bindings.

    Andrew
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