linux-kernel - Re: [RFC] mips: Add MXU context switching support

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Message-ID: <alpine.DEB.2.00.1607051144190.4076@tp.orcam.me.uk>
Date:	Tue, 5 Jul 2016 11:53:17 +0100
From:	"Maciej W. Rozycki" <macro@...tec.com>
To:	PrasannaKumar Muralidharan <prasannatsmkumar@...il.com>
CC:	<linux-mips@...ux-mips.org>, <linux-kernel@...r.kernel.org>,
	Alexey Dobriyan <adobriyan@...il.com>,
	John Stultz <john.stultz@...aro.org>, <mguzik@...hat.com>,
	<athorlton@....com>, <mhocko@...e.com>, <ebiederm@...ssion.com>,
	<gorcunov@...nvz.org>, <luto@...nel.org>, <cl@...ux.com>,
	<serge.hallyn@...ntu.com>, Kees Cook <keescook@...omium.org>,
	<jslaby@...e.cz>, Andrew Morton <akpm@...ux-foundation.org>,
	Florian Fainelli <f.fainelli@...il.com>, <mingo@...nel.org>,
	<alex.smith@...tec.com>, <markos.chandras@...tec.com>,
	Leonid Yegoshin <Leonid.Yegoshin@...tec.com>,
	<david.daney@...ium.com>, <zhaoxiu.zeng@...il.com>,
	<chenhc@...ote.com>, <Zubair.Kakakhel@...tec.com>,
	James Hogan <james.hogan@...tec.com>,
	Paul Burton <paul.burton@...tec.com>,
	Ralf Baechle <ralf@...ux-mips.org>
Subject: Re: [RFC] mips: Add MXU context switching support

On Tue, 5 Jul 2016, PrasannaKumar Muralidharan wrote:

> >> +     asm volatile(".word     0x700803ee\n\t");
> >> +     tsk->thread.mxu.xr[15] = reg_val;
> >> +}
> >
> >  Not using an output operand with asms here?
> 
> I think the instruction saves the xr* register value to reg_val
> without need for output operand.

 It does, a classic `asm' is supposed to act as an optimisation barrier.  

 However since you've used an operand `asm' in `__restore_mxu' I think 
it would be good for consistency to use one here as well; it would make 
this piece of code a little bit more readable too, as you wouldn't have 
to guess that the `asm' writes to `reg_val' then.

 So I suggest that you convert `__save_mxu' to use an operand `asm' as 
well.

  Maciej