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

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Message-ID: <20131127174204.GD27879@e106331-lin.cambridge.arm.com>
Date:	Wed, 27 Nov 2013 17:42:04 +0000
From:	Mark Rutland <mark.rutland@....com>
To:	Jisheng Zhang <jszhang@...vell.com>
Cc:	"rob.herring@...xeda.com" <rob.herring@...xeda.com>,
	Pawel Moll <Pawel.Moll@....com>,
	"swarren@...dotorg.org" <swarren@...dotorg.org>,
	"ijc+devicetree@...lion.org.uk" <ijc+devicetree@...lion.org.uk>,
	"rob@...dley.net" <rob@...dley.net>,
	"linux@....linux.org.uk" <linux@....linux.org.uk>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH] ARM: l2x0: add prefetch and power ctrl registers
 configuration support

On Thu, Nov 07, 2013 at 05:07:52AM +0000, 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.

I'd like to see a reasoning as to _why_ these should be in the DT.

While we have tag and data RAM latency information, those are hardware
properties that we cannot probe. I'm not so clear on the filter-ranges
property.

These bits seem to be configuration rather than a hardware description.
If there are some portions of this that we can describe with higher
level properties, I'd prefer to do that.

But primarily, the question to answer is do we need these, and if so do
they belong in the DT?

> 
> 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.
>  - interrupts : 1 combined interrupt.
>  - cache-id-part: cache id part number to be used if it is not present
>    on hardware
> diff --git a/arch/arm/mm/cache-l2x0.c b/arch/arm/mm/cache-l2x0.c
> index 447da6f..8f536ea 100644
> --- a/arch/arm/mm/cache-l2x0.c
> +++ b/arch/arm/mm/cache-l2x0.c
> @@ -704,6 +704,8 @@ static void __init pl310_of_setup(const struct device_node *np,
>  	u32 data[3] = { 0, 0, 0 };
>  	u32 tag[3] = { 0, 0, 0 };
>  	u32 filter[2] = { 0, 0 };
> +	u32 l2x0_revision = readl_relaxed(l2x0_base + L2X0_CACHE_ID) &
> +		L2X0_CACHE_ID_RTL_MASK;
>  
>  	of_property_read_u32_array(np, "arm,tag-latency", tag, ARRAY_SIZE(tag));
>  	if (tag[0] && tag[1] && tag[2])
> @@ -730,6 +732,23 @@ static void __init pl310_of_setup(const struct device_node *np,
>  		writel_relaxed((filter[0] & ~(SZ_1M - 1)) | L2X0_ADDR_FILTER_EN,
>  			       l2x0_base + L2X0_ADDR_FILTER_START);
>  	}
> +
> +	if (l2x0_revision >= L2X0_CACHE_ID_RTL_R2P0) {
> +		u32 prefetch_ctrl = 0;
> +
> +		of_property_read_u32(np, "arm,prefetch-ctrl",
> +				     &prefetch_ctrl);
> +		if (prefetch_ctrl)
> +			writel_relaxed(prefetch_ctrl, l2x0_base +
> +					L2X0_PREFETCH_CTRL);

Some of the prefetch control regsiter bits are reserved, and the
prefetch offset may only take a subset of possible values. I wouldn't
want to poke the hardware without performing some sanity checking on
these values.

> +		if (l2x0_revision >= L2X0_CACHE_ID_RTL_R3P0) {
> +			u32 pwr_ctrl = 0;
> +			of_property_read_u32(np, "arm,pwr-ctrl", &pwr_ctrl);
> +			if (pwr_ctrl)
> +				writel_relaxed(pwr_ctrl, l2x0_base +
> +						L2X0_POWER_CTRL);

Similarly, all but the lower 2 bits are reserved...

Thanks,
Mark.
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