On Thu, Apr 23, 2015 at 8:27 PM, Greg Kroah-Hartman
<gregkh@xxxxxxxxxxxxxxxxxxx> wrote:
> On Thu, Apr 23, 2015 at 08:06:52PM +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.
>>
>> Signed-off-by: Geert Uytterhoeven <geert@xxxxxxxxxxxxxx>
>> ---
>> drivers/staging/fbtft/fbtft-core.c | 4 ++++
>> 1 file changed, 4 insertions(+)
>>
>> diff --git a/drivers/staging/fbtft/fbtft-core.c b/drivers/staging/fbtft/fbtft-core.c
>> index 53b748be27124793..88bf4705ebadc590 100644
>> --- a/drivers/staging/fbtft/fbtft-core.c
>> +++ b/drivers/staging/fbtft/fbtft-core.c
>> @@ -47,9 +47,13 @@ static unsigned long debug;
>> module_param(debug, ulong, 0);
>> MODULE_PARM_DESC(debug, "override device debug level");
>>
>> +#ifdef CONFIG_HAS_DMA
>> static bool dma = true;
>> module_param(dma, bool, 0);
>> MODULE_PARM_DESC(dma, "Use DMA buffer");
>> +#else
>> +static const bool dma;
>> +#endif
>
> I don't see how this change can fix the build error you show above.
> What am I missing?
You're missing that gcc is optimized optimize away the branch that calls
dmam_alloc_coherent():
if (dma) {
dev->coherent_dma_mask = ~0;
txbuf = dmam_alloc_coherent(dev, txbuflen,
&par->txbuf.dma, GFP_DMA);
} else {
...
}
HOWEVER, please drop this patch.
Originally I had "static const bool dma = false;", but checkpatch rightfully
complained about the initialization of a static, so I dropped it.
Guess what, gcc 4.1.2 no longer optimizes away the branch :-(
Will send v2 in a few minutes.
Gr{oetje,eeting}s,
Geert
--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx
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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