linux-kernel - Re: [PATCH v2] staging: fbtft: Disable DMA support if DMA is not available

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Date:	Thu, 23 Apr 2015 21:17:38 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	Geert Uytterhoeven <geert@...ux-m68k.org>
Cc:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Noralf Trønnes <noralf@...nnes.org>,
	devel@...verdev.osuosl.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] staging: fbtft: Disable DMA support if DMA is not
 available

On Thu, Apr 23, 2015 at 08:47:15PM +0200, Geert Uytterhoeven wrote:
> If NO_DMA=y:
> 
>     drivers/built-in.o: In function `fbtft_framebuffer_alloc':
>     (.text+0xb53cae): undefined reference to `dmam_alloc_coherent'
> 
> As DMA support is already optional, make it depend on HAS_DMA.
> 
> If !HAS_DMA, "dma" will always be false, and the compiler will optimize
> away the call to dmam_alloc_coherent().

Oh that's "sneaky" and not good, let's just make this driver be
dependant on DMA and be done with it.  I don't like to rely on the
optimizer to get things to work properly.

thanks,

greg k-h
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