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

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Message-ID: <527B8BB4.3050200@gmail.com>
Date:	Thu, 07 Nov 2013 13:46:44 +0100
From:	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
To:	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
CC:	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 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.

The same also applies for Prefetch Control register, too.

Sebastian

>   - 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);
> +		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);
> +		}
> +	}
>   }
>
>   static void __init pl310_save(void)
>

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