linux-kernel - Re: [PATCH v4 2/7] arm64: Decouple page size from level of translation tables

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Message-ID: <20140429144052.GJ17007@arm.com>
Date:	Tue, 29 Apr 2014 15:40:52 +0100
From:	Catalin Marinas <catalin.marinas@....com>
To:	Jungseok Lee <jays.lee@...sung.com>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"kvmarm@...ts.cs.columbia.edu" <kvmarm@...ts.cs.columbia.edu>,
	Marc Zyngier <Marc.Zyngier@....com>,
	Christoffer Dall <christoffer.dall@...aro.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	linux-samsung-soc <linux-samsung-soc@...r.kernel.org>,
	"steve.capper@...aro.org" <steve.capper@...aro.org>,
	"sungjinn.chung@...sung.com" <sungjinn.chung@...sung.com>,
	Arnd Bergmann <arnd@...db.de>,
	"kgene.kim@...sung.com" <kgene.kim@...sung.com>,
	"ilho215.lee@...sung.com" <ilho215.lee@...sung.com>
Subject: Re: [PATCH v4 2/7] arm64: Decouple page size from level of
 translation tables

Jungseok,

On Tue, Apr 29, 2014 at 05:59:20AM +0100, Jungseok Lee wrote:
> +choice
> +	prompt "Level of translation tables"
> +	default ARM64_3_LEVELS if ARM64_4K_PAGES
> +	default ARM64_2_LEVELS if ARM64_64K_PAGES
> +	help
> +	  Allows level of translation tables.
> +
> +config ARM64_2_LEVELS
> +	bool "2 level"
> +	depends on ARM64_64K_PAGES
> +	help
> +	  This feature enables 2 levels of translation tables.
> +
> +config ARM64_3_LEVELS
> +	bool "3 level"
> +	depends on ARM64_4K_PAGES
> +	help
> +	  This feature enables 3 levels of translation tables.
> +
> +endchoice

As I mentioned previously
(http://www.spinics.net/linux/lists/arm-kernel/msg319552.html), just
expose options for the VA space bits rather than the number of levels.
You can still keep the number of levels config options but not visible
in menuconfig (though I think you could also hide them in some header
and avoid config altogether). The VA bits config options can be:

VA_BITS_39 if 4K (3 levels)
VA_BITS_42 if 64K (2 levels)
VA_BITS_47 if 16K (3 levels)
VA_BITS_48 if 4K || 16K || 64K (4/4/3 levels depending on page size)

That's more meaningful to people configuring the kernel.

-- 
Catalin
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