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From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To: Christoph Hellwig <hch@lst.de>
Cc: stefan.wahren@i2se.com, f.fainelli@gmail.com,
	catalin.marinas@arm.com, phil@raspberrypi.org,
	Robin Murphy <robin.murphy@arm.com>,
	iommu@lists.linux-foundation.org, linux-kernel@vger.kernel.org,
	Jisheng.Zhang@synaptics.com, mbrugger@suse.com, will@kernel.org,
	linux-arm-kernel@lists.infradead.org,
	Marek Szyprowski <m.szyprowski@samsung.com>
Subject: Re: [RFC 3/4] dma-direct: add dma_direct_min_mask
Date: Thu, 18 Jul 2019 13:18:42 +0200
Message-ID: <13dd1a4f33fcf814545f0d93f18429e853de9eaf.camel@suse.de> (raw)
In-Reply-To: <20190718091526.GA25321@lst.de>

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On Thu, 2019-07-18 at 11:15 +0200, Christoph Hellwig wrote:
> On Wed, Jul 17, 2019 at 05:31:34PM +0200, Nicolas Saenz Julienne wrote:
> > Historically devices with ZONE_DMA32 have been assumed to be able to
> > address at least the lower 4GB of ram for DMA. This is still the defualt
> > behavior yet the Raspberry Pi 4 is limited to the first GB of memory.
> > This has been observed to trigger failures in dma_direct_supported() as
> > the 'min_mask' isn't properly set.
> > 
> > We create 'dma_direct_min_mask' in order for the arch init code to be
> > able to fine-tune dma direct's 'min_dma' mask.
> 
> Normally we use ZONE_DMA for that case.

Fair enough, I didn't think of that possibility.

So would the arm64 maintainers be happy with something like this:

- ZONE_DMA: Follows standard definition, 16MB in size. ARCH_ZONE_DMA_BITS is
	    left as is.
- ZONE_DMA32: Will honor the most constraining 'dma-ranges'. Which so far for
	      most devices is 4G, except for RPi4.
- ZONE_NORMAL: The rest of the memory.


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Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-17 15:31 [RFC 0/4] Raspberry Pi 4 DMA addressing support Nicolas Saenz Julienne
2019-07-17 15:31 ` [RFC 1/4] arm64: mm: use arm64_dma_phys_limit instead of calling max_zone_dma_phys() Nicolas Saenz Julienne
2019-07-17 15:31 ` [RFC 2/4] arm64: mm: parse dma-ranges in order to better estimate arm64_dma_phys_limit Nicolas Saenz Julienne
2019-07-24 13:54   ` Catalin Marinas
2019-07-17 15:31 ` [RFC 3/4] dma-direct: add dma_direct_min_mask Nicolas Saenz Julienne
2019-07-18  9:15   ` Christoph Hellwig
2019-07-18 11:18     ` Nicolas Saenz Julienne [this message]
2019-07-19 13:08       ` Nicolas Saenz Julienne
2019-07-24 13:51         ` Catalin Marinas
2019-07-24 13:56           ` Christoph Hellwig
2019-07-24 14:27             ` Nicolas Saenz Julienne
2019-07-17 15:31 ` [RFC 4/4] arm64: mm: set direct_dma_min_mask according to dma-ranges Nicolas Saenz Julienne

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