linux-kernel - RE: [PATCH/RFC] usb: gadget: CONFIG_USB_S3C_HSOTG should depend on HAS

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Message-ID: <063D6719AE5E284EB5DD2968C1650D6D0F70D180@AcuExch.aculab.com>
Date:	Tue, 6 May 2014 13:17:21 +0000
From:	David Laight <David.Laight@...LAB.COM>
To:	'Geert Uytterhoeven' <geert@...ux-m68k.org>,
	Felipe Balbi <balbi@...com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Ben Dooks <ben.dooks@...ethink.co.uk>
CC:	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH/RFC] usb: gadget: CONFIG_USB_S3C_HSOTG should depend on
 HAS_DMA

From: Geert Uytterhoeven
> If NO_DMA=y:
> 
> drivers/built-in.o: In function `s3c_hsotg_map_dma':
> s3c-hsotg.c:(.text+0x375b2c): undefined reference to `usb_gadget_map_request'
> drivers/built-in.o: In function `s3c_hsotg_unmap_dma':
> s3c-hsotg.c:(.text+0x376a32): undefined reference to `usb_gadget_unmap_request'
> make[3]: *** [vmlinux] Error 1
> 
> Note that all callers of s3c_hsotg_map_dma()/s3c_hsotg_unmap_dma() are
> protected by a call into the using_dma() checking function:
> 
> static inline bool using_dma(struct s3c_hsotg *hsotg)
> {
>         return false;   /* support is not complete */
> }
> 
> but not all versions of gcc manage to optimize the check away, causing a
> link error.

A have seen gcc optimise away a call, but leave the undefined symbol
in the symbol table.
That might be what is happening here.

I don't know a generic solution, I used 'objcopy -N__udivdi3' to remove
the explicit unwanted reference from my driver.

	David



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