linux-kernel - Re: [PATCH v4 5/7] ARM: EXYNOS: Add .write

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Date:	Mon, 15 Sep 2014 09:58:45 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Tomasz Figa <t.figa@...sung.com>
Cc:	linux-samsung-soc@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Kukjin Kim <kgene.kim@...sung.com>, lauraa@...eaurora.org,
	linux-omap@...r.kernel.org, linus.walleij@...aro.org,
	santosh.shilimkar@...com, tony@...mide.com, drake@...lessm.com,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Tomasz Figa <tomasz.figa@...il.com>, loeliger@...il.com
Subject: Re: [PATCH v4 5/7] ARM: EXYNOS: Add .write_sec outer cache
	callback for L2C-310

On Tue, Aug 26, 2014 at 04:17:58PM +0200, Tomasz Figa wrote:
> Exynos4 SoCs equipped with an L2C-310 cache controller and running under
> secure firmware require certain registers of aforementioned IP to be
> accessed only from secure mode. This means that SMC calls are required
> for certain register writes. To handle this, an implementation of
> .write_sec and .configure callbacks is provided by this patch.
> 
> Signed-off-by: Tomasz Figa <t.figa@...sung.com>
> ---
>  arch/arm/mach-exynos/firmware.c | 38 ++++++++++++++++++++++++++++++++++++++
>  1 file changed, 38 insertions(+)
> 
> diff --git a/arch/arm/mach-exynos/firmware.c b/arch/arm/mach-exynos/firmware.c
> index f5e626d..554b350 100644
> --- a/arch/arm/mach-exynos/firmware.c
> +++ b/arch/arm/mach-exynos/firmware.c
> @@ -17,6 +17,7 @@
>  #include <asm/cacheflush.h>
>  #include <asm/cputype.h>
>  #include <asm/firmware.h>
> +#include <asm/hardware/cache-l2x0.h>
>  #include <asm/suspend.h>
>  
>  #include <mach/map.h>
> @@ -120,6 +121,31 @@ static const struct firmware_ops exynos_firmware_ops = {
>  	.resume			= exynos_resume,
>  };
>  
> +static void exynos_l2_write_sec(unsigned long val, unsigned reg)
> +{
> +	switch (reg) {
> +	case L2X0_CTRL:
> +		if (val & L2X0_CTRL_EN)
> +			exynos_smc(SMC_CMD_L2X0INVALL, 0, 0, 0);

If we're calling this with the cache already enabled, presumably you're
doing this to cover the case where we're disabling the cache.

1. Do you really want to *invalidate* the L2 cache, discarding its
   contents?
2. Don't you think that... if you needed something like this here, then
   it could be a defficiency in the common code?

If (2) doesn't apply, then should be a comment here why this is needed.

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