Hi Bjorn, On 09/02/2016 11:12 PM, Bjorn Andersson wrote: > On Fri 02 Sep 04:52 PDT 2016, Marek Szyprowski wrote: > >> Hi, >> >> >> On 2016-09-01 16:58, Stanimir Varbanov wrote: >>> Hi, >>> >>> Cc: Marek >>> >> >> ... >> >>>>>> But I presume we have the implementation issue of dma_alloc_coherent() >>>>>> failing in either case with the 5MB size. I think we need to look into >>>>> I'd be good to include Marek Szyprowski? At least he will know what >>>>> design restrictions there are. >>>>> >>>> Please do. The more I look at this the more I think we must use the >>>> existing infrastructure for allocating "dma memory". Getting >>>> dma_alloc_coherent() supporting non-power-of-2 memory regions would >>> Just to be precise it should be dma_alloc_from_coherent(). >>> >>> Marek, what is your opinion on that, can we make dma_alloc_from_coherent >>> able to allocate memory for sizes with bigger granularity. >>> >>> For your convenience here [1] is the mail thread. >> >> There should be no technical restrictions to add support for bigger >> granularity than power-of-2. dma_alloc_from_coherent uses standard >> bitmap based allocator, so it already support tracking allocations of >> arbitrary size. > > I believe we should be able to change the parameter of > bitmap_{find_free,release,allocate}_region() to take a size rather than > an order. > > The mask used in __reg_op() is an unsigned long, that is stamped over > the region to be masked or cleared, so there are some clear restrictions > in what parameters we can pass there - without having to break this > operation up in steps. > > But if drive the offset by taking the next power-of-two of the size and > then align the number of bits to min(count, BITS_PER_LONG) we should > retain the performance characteristics and requirements of __reg_op(). > >> However for the small allocations (smaller than 64KiB?, 512KiB?) it >> would make sense to keep nearest-power-of-2 round up to prevent memory >> fragmentation. > > But in our case each bit matches a single page, so by making sure the > mask always fills the unsigned long in the larger cases we would end up > with having to align things to 128kb (or 256kb if unsigned long is 64 > bit). > > > Does this sound reasonable? I haven't looked in bitmap details, but can't we reuse genalloc? -- regards, Stan -- To unsubscribe from this list: send the line "unsubscribe devicetree" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html