linux-kernel - Re: [PATCH v2 3/4] x86: intel-mid: add Merrifield platform support

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Date:	Mon, 27 Jan 2014 17:52:30 -0700
From:	Bjorn Helgaas <bhelgaas@...gle.com>
To:	David Cohen <david.a.cohen@...ux.intel.com>
Cc:	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	"x86@...nel.org" <x86@...nel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Fei Yang <fei.yang@...el.com>,
	"Mark F. Brown" <mark.f.brown@...el.com>,
	Kuppuswamy Sathyanarayanan 
	<sathyanarayanan.kuppuswamy@...ux.intel.com>
Subject: Re: [PATCH v2 3/4] x86: intel-mid: add Merrifield platform support

On Mon, Dec 16, 2013 at 1:07 PM, David Cohen
<david.a.cohen@...ux.intel.com> wrote:
> This code was partially based on Mark Brown's previous work.
>
> Signed-off-by: David Cohen <david.a.cohen@...ux.intel.com>
> Signed-off-by: Fei Yang <fei.yang@...el.com>
> Cc: Mark F. Brown <mark.f.brown@...el.com>
> Cc: Kuppuswamy Sathyanarayanan <sathyanarayanan.kuppuswamy@...ux.intel.com>

I know this has already been merged to Linus' tree, but it looks funny to me.

> --- a/arch/x86/platform/intel-mid/intel_mid_weak_decls.h
> +++ b/arch/x86/platform/intel-mid/intel_mid_weak_decls.h
> @@ -16,3 +16,4 @@
>   */
>  extern void * __cpuinit get_penwell_ops(void) __attribute__((weak));
>  extern void * __cpuinit get_cloverview_ops(void) __attribute__((weak));
> +extern void * __init get_tangier_ops(void) __attribute__((weak));

We should use "__weak" instead of the gcc-specific "__attribute__((weak))".

I don't think it's a good idea to use __weak on a declaration in a
header file.  If there are ever multiple definitions of the symbol,
they are *all* made weak symbols, and one is chosen based on link
order, which is error-prone.  I only see one definition now, but the
whole point of weak is to allow multiple definitions, so this looks
like a problem waiting to happen.  See 10629d711ed, for example.

It look me a bit to figure out that these get_*_ops() functions are
used by INTEL_MID_OPS_INIT, which constructs the name using a macro,
so grep/cscope/etc. don't see any users.  A comment pointing to
INTEL_MID_OPS_INIT would be helpful.

What's the reason for making these symbols weak?  Normally we use weak
to make a generic default version of a function, while allowing
architectures to replace the default with their own version if
necessary.  But I don't see that happening here.  Maybe I'm just
missing it, like I missed the uses of get_tangier_ops(), et al.

Bjorn
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