linux-kernel - Re: [PATCH] MIPS: Allow R6 compact branch policy to be left unspecified

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Message-ID: <alpine.DEB.2.00.1605111412420.6794@tp.orcam.me.uk>
Date:	Wed, 11 May 2016 14:22:05 +0100
From:	"Maciej W. Rozycki" <macro@...tec.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
CC:	James Hogan <james.hogan@...tec.com>,
	Paul Burton <paul.burton@...tec.com>,
	<linux-mips@...ux-mips.org>, <fengguang.wu@...el.com>,
	"stable # v4 . 4+" <stable@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] MIPS: Allow R6 compact branch policy to be left
 unspecified

On Wed, 11 May 2016, Ralf Baechle wrote:

> I was wondering if we should simply probe for the availability of the
> GCC option and not use it, if using an older GCC, then change the
> help text for the option accordingly.  This approach would allow
> make randconfig or similar to work as expected with older compilers.

 Well, if the default is `optimal' anyway, then I think we can simply omit 
the option unless someone has requested an override.  In which case I 
think the compilation should fail if the option is not supported, under 
the principle of the least surprise -- if someone has requested a feature, 
then they ought to be informed that it is absent rather than silently 
fooled into thinking it has been enabled while in fact it has not.

 I agree probing for the presence of the option requested and then failing 
gracefully (e.g. "Toolchain feature FOO not available, please upgrade or 
reconfigure without BAR" or suchlike) is a better idea than just aborting 
midway through, and I think `randconfig' and similar validators should be 
prepared for it and handle gracefully as well (i.e. not a kernel bug).

 FWIW,

  Maciej