From mboxrd@z Thu Jan 1 00:00:00 1970 From: Christoph Hellwig Subject: Re: [PATCH v2] dma-direct: do not allocate a single page from CMA area Date: Wed, 6 Feb 2019 08:07:26 +0100 Message-ID: <20190206070726.GE23392@lst.de> References: <20190115215140.1545-1-nicoleotsuka@gmail.com> <20190204082307.GA5916@lst.de> <20190205230514.GA21515@Asurada-Nvidia.nvidia.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: <20190205230514.GA21515@Asurada-Nvidia.nvidia.com> Sender: linux-kernel-owner@vger.kernel.org To: Nicolin Chen Cc: Christoph Hellwig , m.szyprowski@samsung.com, robin.murphy@arm.com, vdumpa@nvidia.com, iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org List-Id: iommu@lists.linux-foundation.org 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); } /**