linux-kernel - Re: [PATCH] usb: usb_phy_gen: refine conditional declaration of usb_nop_xceiv

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Date:	Thu, 17 Oct 2013 13:31:47 -0700
From:	Guenter Roeck <linux@...ck-us.net>
To:	Josh Boyer <jwboyer@...hat.com>
Cc:	linux-kernel@...r.kernel.org, linux-usb@...r.kernel.org,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [PATCH] usb: usb_phy_gen: refine conditional declaration of
 usb_nop_xceiv_register

On Thu, Oct 17, 2013 at 01:25:48PM -0400, Josh Boyer wrote:
> On Wed, Oct 16, 2013 at 07:18:41PM -0700, Guenter Roeck wrote:
> > Commit 3fa4d734 (usb: phy: rename nop_usb_xceiv => usb_phy_gen_xceiv)
> > changed the conditional around the declaration of usb_nop_xceiv_register
> > from
> > 	#if defined(CONFIG_NOP_USB_XCEIV) ||
> > 		(defined(CONFIG_NOP_USB_XCEIV_MODULE) && defined(MODULE))
> > to
> > 	#if IS_ENABLED(CONFIG_NOP_USB_XCEIV)
> > 
> > While that looks the same, it is semantically different. The first expression
> > is true if CONFIG_NOP_USB_XCEIV is built as module and if the including
> > code is built as module. The second expression is true if code depending on
> > CONFIG_NOP_USB_XCEIV if built as module or into the kernel.
> > 
> > As a result, the arm:allmodconfig build fails with
> > 
> > arch/arm/mach-omap2/built-in.o: In function `omap3_evm_init':
> > arch/arm/mach-omap2/board-omap3evm.c:703: undefined reference to
> > 	`usb_nop_xceiv_register'
> > 
> > Fix the problem by reverting to the old conditional.
> > 
> > Cc: Josh Boyer <jwboyer@...hat.com>
> > Signed-off-by: Guenter Roeck <linux@...ck-us.net>
> 
> I'm not entirely sure why I was CC'd on this one, but the patch looks
> good to me.  I do wonder how many other uses of IS_ENABLED aren't taking
> this into account though.
> 
Unless I am wrong, you submitted a different patch to fix the same problem,
which went nowhere, so I figured it was appropriate to Cc: you on this one.
If not, my apologies.

As for other use cases of IS_ENABLED, agreed, that may be an ongoing concern. 
That will have to be addressed individually, though.

Thanks,
Guenter
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