On Mon, 19 Mar 2012, Mauro Carvalho Chehab wrote: > Em 20-02-2012 16:23, Fabio Estevam escreveu: > > On Mon, Feb 20, 2012 at 4:17 PM, Guennadi Liakhovetski > > <g.liakhovetski@xxxxxx> wrote: > >> On Mon, 20 Feb 2012, Fabio Estevam wrote: > >> > >>> Align mx3_camera driver with the other soc camera driver implementations > >>> by allocating the camera object via kzalloc. > >> > >> Sorry, any specific reason, why you think this "aligning" is so important? > > > > Not really. > > > > Just compared it with all other soc camera drivers I found and > > mx3_camera was the only one that uses "vzalloc" > > > > Any specific reason that requires mx3_camera to use "vzalloc" instead > > of "kzalloc"? > > kzalloc() is more restrictive than vzalloc(). With v*alloc, it will allocate > a virtual memory area, with can be discontinuous, while kzalloc will get > a continuous area. > > The DMA logic need to be prepared for virtual memory, if v*alloc() is used > (e. g. using videobuf2-vmalloc). > > As it is currently including media/videobuf2-dma-contig.h, I this patch > makes sense on my eyes. Don't think so. vzalloc() is used in mx3_camera to allocate driver private data objects and are never used for DMA, so, it doesn't have any restrictions on contiguity, coherency, alignment etc. One could argue, that since the struct is anyway smaller than 1 page, it anyway will be allocated in a physically contiguous memory area (will it?) and so, maybe, kmalloc() is less heavy weight than vmalloc() and might save a couple of CPU cycles, but I don't think it's anything important, that we should be optimising for. Thanks Guennadi --- Guennadi Liakhovetski, Ph.D. Freelance Open-Source Software Developer http://www.open-technology.de/ -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
