From mboxrd@z Thu Jan  1 00:00:00 1970
From: linux@arm.linux.org.uk (Russell King - ARM Linux)
Date: Fri, 19 Mar 2010 08:53:17 +0000
Subject: [PATCH] arm: Replace CONFIG_HAS_TLS_REG with HWCAP_TLS and
	check for it on V6
In-Reply-To: <20100319013521.GP2900@atomide.com>
References: <20100317175731.GE2900@atomide.com>
	<1268849278.19565.28.camel@e102109-lin.cambridge.arm.com>
	<20100317191114.GH2900@atomide.com>
	<1268910826.15334.32.camel@e102109-lin.cambridge.arm.com>
	<20100318170021.GN2900@atomide.com>
	<20100319013521.GP2900@atomide.com>
Message-ID: <20100319085317.GA8451@n2100.arm.linux.org.uk>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Thu, Mar 18, 2010 at 06:35:21PM -0700, Tony Lindgren wrote:
> -#if defined(CONFIG_HAS_TLS_REG)
> -	mcr	p15, 0, r3, c13, c0, 3		@ set TLS register
> -#elif !defined(CONFIG_TLS_REG_EMUL)
> -	mov	r4, #0xffff0fff
> -	str	r3, [r4, #-15]			@ TLS val at 0xffff0ff0
> +#if !defined(CONFIG_TLS_REG_EMUL)
> +	ldr	r4, =elf_hwcap
> +	ldr	r4, [r4, #0]
> +	tst	r4, #HWCAP_TLS			@ hardware with TLS?

This is really really inefficient.  Both the second ldr and tst will stall
the pipeline because they need to wait for the result of the precending
ldr.  Can we do better by re-ordering some instructions?

Also, the ifndef seems incorrect - if we have TLS_REG_EMUL we seem to omit
all this code.