linux-kernel - Re: [v2,3/6] powerpc: kill mfvtb()

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Message-ID: <20150908025923.GD24733@pek-khao-d1.corp.ad.wrs.com>
Date:	Tue, 8 Sep 2015 10:59:23 +0800
From:	Kevin Hao <haokexin@...il.com>
To:	Michael Ellerman <mpe@...erman.id.au>
Cc:	Peter Zijlstra <peterz@...radead.org>,
	linuxppc-dev@...ts.ozlabs.org, Ingo Molnar <mingo@...nel.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [v2,3/6] powerpc: kill mfvtb()

On Mon, Sep 07, 2015 at 07:29:42PM +1000, Michael Ellerman wrote:
> On Mon, 2015-24-08 at 11:20:25 UTC, Kevin Hao wrote:
> > This function is only used by get_vtb(). They are almost the same
> > except the reading from the real register. Move the mfspr() to
> > get_vtb() and kill the function mfvtb(). With this, we can eliminate
> > the use of cpu_has_feature() in very core header file like reg.h.
> > This is a preparation for the use of jump label for cpu_has_feature().
> 
> I don't mind this change. But can you elaborate a bit on the issue with using
> cpu_has_feature() in reg.h? Just so I can understand the problem.
> 
> I assume you ended up in a big mess of includes when you tried to include
> jump_label.h from reg.h?

Yes, the "jump_leabel.h" already include "reg.h" implicitly. 
   from arch/powerpc/include/asm/cache.h:6:0,
   from include/linux/cache.h:5,
   from include/linux/printk.h:8,
   from include/linux/kernel.h:14,
   from include/asm-generic/bug.h:13,
   from arch/powerpc/include/asm/bug.h:127,
   from include/linux/bug.h:4,
   from include/linux/jump_label.h:81,

So including "jump_label.h" from "reg.h" will cause a recursive header
inclusion problem.

Thanks,
Kevin

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