Messages in this thread Patch in this message | | | Date | Wed, 6 Feb 2019 08:07:26 +0100 | From | Christoph Hellwig <> | Subject | Re: [PATCH v2] dma-direct: do not allocate a single page from CMA area |
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On Tue, Feb 05, 2019 at 03:05:30PM -0800, Nicolin Chen wrote: > > And my other concern is that this skips allocating from the per-device > > pool, which drivers might rely on. > > Actually Robin had the same concern at v1 and suggested that we could > always use DMA_ATTR_FORCE_CONTIGUOUS to enforce into per-device pool.
That is both against the documented behavior of DMA_ATTR_FORCE_CONTIGUOUS and doesn't help existing drivers that specify their CMA area in DT.
> > To be honest I'm not sure there is > > much of a point in the per-device CMA pool vs the traditional per-device > > coherent pool, but I'd rather change that behavior in a clearly documented > > commit with intentions rather as a side effect from a random optimization. > > Hmm..sorry, I don't really follow this suggestion. Is it possible for > you to make it clear that what should I do for the change?
Something like this (plus proper comments):
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c index b2a87905846d..789d734f0f77 100644 --- a/kernel/dma/contiguous.c +++ b/kernel/dma/contiguous.c @@ -192,10 +192,19 @@ int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base, struct page *dma_alloc_from_contiguous(struct device *dev, size_t count, unsigned int align, bool no_warn) { + struct cma *cma; + if (align > CONFIG_CMA_ALIGNMENT) align = CONFIG_CMA_ALIGNMENT; - return cma_alloc(dev_get_cma_area(dev), count, align, no_warn); + if (dev && dev->cma_area) + cma = dev->cma_area; + else if (count > PAGE_SIZE) + cma = dma_contiguous_default_area; + else + return NULL; + + return cma_alloc(cma, count, align, no_warn); } /**
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