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

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Message-ID: <20150205224439.GA19250@e104818-lin.cambridge.arm.com>
Date:	Thu, 5 Feb 2015 22:44:40 +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

Murali,

On Thu, Feb 05, 2015 at 09:42:27PM +0000, Murali Karicheri wrote:
> On 02/02/2015 07:18 AM, Catalin Marinas wrote:
> > 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.
> 
> The size based dma mask calculation itself can be a separate topic 
> patch. This series is adding important fix to get the PCI driver 
> functional and I would like to get this merged as soon as possible.

Well as long as you don't break the existing users of
of_dma_configure() ;).

> I also want to hear from Arnd about yout comment as we had discussed
> this in the initial discussion of this patch series and 8/8 is
> essentially added based on that discussion. I will add a simple check
> to catch and warn the incorrect size setting in DT for dma-range as
> suggested by Rob Herring and create a new patch to for size based mask
> calculation. I will be sending v6 (expected to be merged soon) today
> and will work to add a new patch. Before that we need to agree on what
> is the content of the patch.
> 
> 1. On keystone, DMA address start at 0x8000_0000 and DMA-able memory is 
> 2G from the above base address. So without taking into account the
> dma_addr, mask calculated will be 0x7fff_ffff where as we need that to 
> be 0xffff_ffff for keystone. So need to use this in the calculation.

Ah, you are right. I confused dma_addr in your patch with the offset.

> 2. W.r.t arm_pfn_offset, this was added to support Keystone as the DDR 
> physical address for LPAE startes at 0x8_0000_0000 and the pfn offset is 
> calculated as the PFN of (0x8_0000_0000 - 0x8000_0000) to do the dma 
> address to DDR address translation.

Indeed.

I'll look at your patches again tomorrow.

-- 
Catalin
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