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

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Date:	Fri, 24 Apr 2015 09:15:00 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
	Noralf Trønnes <noralf@...nnes.org>,
	driverdevel <devel@...verdev.osuosl.org>,
	"linux-kernel@...r.kernel.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 9:17 PM, Greg Kroah-Hartman
<gregkh@...uxfoundation.org> wrote:
> 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.

Alternatively, I can stick in one more #ifdef, to no longer rely on the compiler
optimization?
AFAICS, the driver itself considers DMA optional, and will work without.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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