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    SubjectRe: [PATCH v2] staging: fbtft: Disable DMA support if DMA is not available
    On Fri, Apr 24, 2015 at 09:15:00AM +0200, Geert Uytterhoeven wrote:
    > On Thu, Apr 23, 2015 at 9:17 PM, Greg Kroah-Hartman
    > <gregkh@linuxfoundation.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?

    That would be better.

    thanks,

    greg k-h


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