linux-kernel - Re: [PATCH v4 3/6] of: fix size when dma-range is not used

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Date:	Mon, 2 Feb 2015 12:18:43 +0000
From:	Catalin Marinas <catalin.marinas@....com>
To:	Murali Karicheri <m-karicheri2@...com>
Cc:	Robin Murphy <Robin.Murphy@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Arnd Bergmann <arnd@...db.de>,
	"linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
	Joerg Roedel <joro@...tes.org>,
	Will Deacon <Will.Deacon@....com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"grant.likely@...aro.org" <grant.likely@...aro.org>,
	"iommu@...ts.linux-foundation.org" <iommu@...ts.linux-foundation.org>,
	Rob Herring <robh+dt@...nel.org>,
	"suravee.suthikulpanit@....com" <suravee.suthikulpanit@....com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v4 3/6] of: fix size when dma-range is not used

On Fri, Jan 30, 2015 at 06:06:27PM +0000, Murali Karicheri wrote:
> On 01/28/2015 12:30 PM, Catalin Marinas wrote:
> > I think we can remove this check altogether (we leaved without it for a
> > while) but we need to add 1 when calculating the mask:
> >
> > 	dev->coherent_dma_mask = min(DMA_BIT_MASK(32),
> > 				     DMA_BIT_MASK(ilog2(size + 1)));
> >
> For Keystone, the dma_addr is to be taken care as well to determine the 
> mask. The above will not work.

This was discussed before (not on this thread) and dma_addr should not
affect the mask, it only affects the pfn offset.

> Based on the discussion so far, this is the function I have come up with 
> incorporating the suggestions. Please review this and see if I have 
> missed out any. This works fine on Keystone.
> 
> void of_dma_configure(struct device *dev, struct device_node *np)
> {
> 	u64 dma_addr = 0, paddr, size;
> 	int ret;
> 	bool coherent;
> 	unsigned long offset = 0;
> 	struct iommu_ops *iommu;
> 
> 	/*
> 	 * Set default size to cover the 32-bit. Drivers are expected to setup
> 	 * the correct size and dma_mask.
>    	 */
> 	size = 1ULL << 32;
> 
> 	ret = of_dma_get_range(np, &dma_addr, &paddr, &size);
> 	if (!ret) {
> 		offset = PFN_DOWN(paddr - dma_addr);
> 		if (!size) {
> 			dev_err(dev, "Invalid size (%llx)\n",
> 				size);
> 			return;
> 		}
> 		if (size & 1) {
> 			size = size + 1;
> 			dev_warn(dev, "Incorrect usage of size (%llx)\n",
> 				 size);
> 		}
> 		dev_dbg(dev, "dma_pfn_offset(%#08lx)\n", offset);
> 	}
> 	dev->dma_pfn_offset = offset;
> 
> 	/*
> 	 * Coherent DMA masks larger than 32-bit must be explicitly set by the
> 	 * driver.
> 	 */
> 	dev->coherent_dma_mask = min(DMA_BIT_MASK(32),
> 				     DMA_BIT_MASK(ilog2(dma_addr + size)));

That's not correct, coherent_dma_mask should still be calculated solely
based on size, not dma_addr.

Functions like swiotlb_dma_supported() use phys_to_dma() which on ARM
(32-bit) subtracts the dma_pfn_offset, so the mask based on size works
fine.

In the arm64 tree, we haven't taken dma_pfn_offset into account for
phys_to_dma() yet but if needed for a SoC, we'll add it.

-- 
Catalin
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