Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [PATCH V3 3/4] dmaselftest: add memcpy selftest support functions | Date | Tue, 10 Nov 2015 11:13:24 +0100 |
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On Monday 09 November 2015 23:49:54 Sinan Kaya wrote: > On 11/9/2015 8:48 AM, Timur Tabi wrote: > > Sinan Kaya wrote: > >>> > >>> And why kmalloc anyway? Why not leave it on the stack? > >>> > >>> char src[] = "hello world"; > >>> > >>> ? > >> > >> I need to call dma_map_single on this address to convert it to a DMA > >> address. That's why. > > > > And you can't do that with an object that's on the stack? > > > > no, pasting from here. > > https://www.kernel.org/doc/Documentation/DMA-API-HOWTO.txt > > under 'What memory is DMA'able?' > > This rule also means that you may use neither kernel image addresses > (items in data/text/bss segments), nor module image addresses, nor > stack addresses for DMA.
Correct. I think this is just because of cache line alignment that is guaranteed for kmalloc but not for anything on the stack.
Arnd
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