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

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Message-ID: <CAErSpo52sXXKkJZ=bMMZw4G0Z0AJ=-u+Ov14+qp=S+y9LCP=Rg@mail.gmail.com>
Date:	Tue, 28 Jan 2014 11:40:57 -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, Jan 27, 2014 at 6:30 PM, David Cohen
<david.a.cohen@...ux.intel.com> wrote:
> Hi Bjorn,
>
> On Mon, Jan 27, 2014 at 05:52:30PM -0700, Bjorn Helgaas wrote:
>> 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.
>
> Intel mid was implemented in such way that we should select which soc to
> be used in compilation time. Depending on the selection, mfld.c or
> mrfl.c could not be compiled then some symbols wouldn't be available.
>
> But IMHO this is a bad legacy design that exists in there, so I started
> to rework it as you can see in this commit:
>
> commit 4cb9b00f42e07830310319a07e6c91413ee8153e
> Author: David Cohen <david.a.cohen@...ux.intel.com>
> Date:   Mon Dec 16 17:37:26 2013 -0800
>
>     x86, intel-mid: Remove deprecated X86_MDFLD and X86_WANT_INTEL_MID
>     configs
>
> I'm sending more patches soon and getting rid of intel_mid_weak_decls.h
> file is in my TODO list.

Sounds good.  While you're looking at it, I have similar questions
about ipc_device_handler() and msic_generic_platform_data().  It's not
clear to me why they should be weak.

Bjorn
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