linux-kernel - Re: [PATCH] ARM: at91: sama5: configure L2 cache

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Message-ID: <20140918210212.GD5182@n2100.arm.linux.org.uk>
Date:	Thu, 18 Sep 2014 22:02:12 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Alexandre Belloni <alexandre.belloni@...e-electrons.com>
Cc:	Nicolas Ferre <nicolas.ferre@...el.com>,
	Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Wenyou Yang <wenyou.yang@...el.com>
Subject: Re: [PATCH] ARM: at91: sama5: configure L2 cache

On Thu, Sep 18, 2014 at 10:38:36PM +0200, Alexandre Belloni wrote:
> From: Wenyou Yang <wenyou.yang@...el.com>
> 
> Ensure that the L2 cache configuration is optimal to avoid depending on the
> bootloader to set it correctly.
> 
> Signed-off-by: Wenyou Yang <wenyou.yang@...el.com>
> Signed-off-by: Alexandre Belloni <alexandre.belloni@...e-electrons.com>
> ---
>  arch/arm/mach-at91/board-dt-sama5.c | 47 ++++++++++++++++++++++++++++++++++++-
>  1 file changed, 46 insertions(+), 1 deletion(-)
> 
> diff --git a/arch/arm/mach-at91/board-dt-sama5.c b/arch/arm/mach-at91/board-dt-sama5.c
> index 548de4ad6937..7cbe0d9daf2b 100644
> --- a/arch/arm/mach-at91/board-dt-sama5.c
> +++ b/arch/arm/mach-at91/board-dt-sama5.c
> @@ -13,12 +13,14 @@
>  #include <linux/gpio.h>
>  #include <linux/micrel_phy.h>
>  #include <linux/of.h>
> +#include <linux/of_address.h>
>  #include <linux/of_irq.h>
>  #include <linux/of_platform.h>
>  #include <linux/phy.h>
>  #include <linux/clk-provider.h>
>  
>  #include <asm/setup.h>
> +#include <asm/hardware/cache-l2x0.h>
>  #include <asm/irq.h>
>  #include <asm/mach/arch.h>
>  #include <asm/mach/map.h>
> @@ -35,8 +37,52 @@ static void __init sama5_dt_timer_init(void)
>  	at91sam926x_pit_init();
>  }
>  
> +static void __init at91_l2x0_init(void)
> +{
> +	struct device_node *np;
> +	void __iomem *l2cc_base;
> +	u32 reg;
> +
> +	np = of_find_compatible_node(NULL, NULL, "arm,pl310-cache");
> +	if (!np)
> +		return;
> +
> +	l2cc_base = of_iomap(np, 0);
> +	of_node_put(np);
> +
> +	if (!l2cc_base) {
> +		pr_err("L2C-310 unable to map registers\n");
> +		return;
> +	}
> +
> +	/* Prefetch Control */
> +	reg = readl_relaxed(l2cc_base + L310_PREFETCH_CTRL);
> +	reg &= ~L310_PREFETCH_CTRL_OFFSET_MASK;
> +	reg |= 0x01 & L310_PREFETCH_CTRL_OFFSET_MASK;
> +	reg |= L310_PREFETCH_CTRL_DBL_LINEFILL_INCR;
> +	reg |= L310_PREFETCH_CTRL_PREFETCH_DROP;
> +	reg |= L310_PREFETCH_CTRL_DATA_PREFETCH;
> +	reg |= L310_PREFETCH_CTRL_INSTR_PREFETCH;
> +	reg |= L310_PREFETCH_CTRL_DBL_LINEFILL;
> +	writel_relaxed(reg, l2cc_base + L310_PREFETCH_CTRL);
> +
> +	/* Power Control */
> +	reg = readl_relaxed(l2cc_base + L310_POWER_CTRL);
> +	reg |= L310_STNDBY_MODE_EN;
> +	reg |= L310_DYNAMIC_CLK_GATING_EN;
> +	writel_relaxed(reg, l2cc_base + L310_POWER_CTRL);
> +
> +	/* Disable interrupts */
> +	writel_relaxed(0x00, l2cc_base + L2X0_INTR_MASK);
> +	writel_relaxed(0x01ff, l2cc_base + L2X0_INTR_CLEAR);
> +
> +	l2x0_of_init(0, ~0UL);

NAK.  Really, nak.  Stop this mentality of working around shortcomings
of generic code by adding yet more platform junk.  Such approaches are
not acceptable.

The power control is already done by generic code.  I know that you've
developed the above code against the exact copy of generic code which
has this, because you're using the new symbols.

You shouldn't need to disable interrupts; the interrupts should already
be disabled unless your bootloaders are doing something weird with them.

There have been DT bindings proposed for prefetch control register.  I
suggest that you search this mailing list for that patch, and check
whether it is acceptable for your platform.

Taking all that together, you should need /zero/ code in your platform
for L2 caches, which is *the way it should be*.

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