From mboxrd@z Thu Jan  1 00:00:00 1970
From: will.deacon@arm.com (Will Deacon)
Date: Wed, 18 Mar 2015 10:30:14 +0000
Subject: [PATCH 2/2] ARM: psci: move psci firmware calls out of line
In-Reply-To: <20150318102029.GC8656@n2100.arm.linux.org.uk>
References: <1424866236-12482-1-git-send-email-will.deacon@arm.com>
 <1424866236-12482-2-git-send-email-will.deacon@arm.com>
 <20150318102029.GC8656@n2100.arm.linux.org.uk>
Message-ID: <20150318103014.GD18951@arm.com>
To: linux-arm-kernel@lists.infradead.org
List-Id: linux-arm-kernel.lists.infradead.org

On Wed, Mar 18, 2015 at 10:20:29AM +0000, Russell King - ARM Linux wrote:
> On Wed, Feb 25, 2015 at 12:10:36PM +0000, Will Deacon wrote:
> > -/*
> > - * The following two functions are invoked via the invoke_psci_fn pointer
> > - * and will not be inlined, allowing us to piggyback on the AAPCS.
> > - */
> > -static noinline int __invoke_psci_fn_hvc(u32 function_id, u32 arg0, u32 arg1,
> > -					 u32 arg2)
> > -{
> > -	asm volatile(
> > -			__asmeq("%0", "r0")
> > -			__asmeq("%1", "r1")
> > -			__asmeq("%2", "r2")
> > -			__asmeq("%3", "r3")
> > -			__HVC(0)
> > -		: "+r" (function_id)
> > -		: "r" (arg0), "r" (arg1), "r" (arg2));
> > -
> > -	return function_id;
> > -}
> 
> Why not convert these to:
> 
> static int __naked __invoke_psci_fn_hvc(u32 function_id, u32 arg0, u32 arg1,
> 					u32 arg2)
> {
> 	asm(
> 		__HVC(0)
> 		"bx lr");
> }
> 
> ?

I tried this, but the compiler printed a diagnostic along the lines of
"Ignoring __naked attribute", so we moved the functions out-of-line like
we have on arm64 instead. Assuming it worked reliably, what's the
advantage of __naked over having these out-of-line?

Will