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From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To: Christoph Hellwig <hch@lst.de>,
	Catalin Marinas <catalin.marinas@arm.com>
Cc: stefan.wahren@i2se.com, Jisheng.Zhang@synaptics.com,
	f.fainelli@gmail.com, will@kernel.org, phil@raspberrypi.org,
	linux-kernel@vger.kernel.org, iommu@lists.linux-foundation.org,
	mbrugger@suse.com, Robin Murphy <robin.murphy@arm.com>,
	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: Wed, 24 Jul 2019 16:27:55 +0200
Message-ID: <3a2f952e090d972b33f62592b12399f9ef3b0513.camel@suse.de> (raw)
In-Reply-To: <20190724135657.GA9075@lst.de>

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On Wed, 2019-07-24 at 15:56 +0200, Christoph Hellwig wrote:
> On Wed, Jul 24, 2019 at 02:51:24PM +0100, Catalin Marinas wrote:
> > I think it may be better if we have both ZONE_DMA and ZONE_DMA32 on
> > arm64. ZONE_DMA would be based on the smallest dma-ranges as described
> > in the DT while DMA32 covers the first naturally aligned 4GB of RAM
> > (unchanged). When a smaller ZONE_DMA is not needed, it could be expanded
> > to cover what would normally be ZONE_DMA32 (or could we have ZONE_DMA as
> > 0-bytes? I don't think GFP_DMA can still allocate memory in this case).
> > 
> > We'd probably have to define ARCH_ZONE_DMA_BITS for arm64 to something
> > smaller than 32-bit but sufficient to cover the known platforms like
> > RPi4 (the current 24 is too small, so maybe 30). AFAICT,
> > __dma_direct_optimal_gfp_mask() figures out whether GFP_DMA or GFP_DMA32
> > should be passed.
> 
> ARCH_ZONE_DMA_BITS should probably become a variable.  That way we can
> just initialize it to the default 24 bits in kernel/dma/direct.c and
> allow architectures to override it in their early boot code.

Thanks both for your feedback. I'll start preparing a proper series.


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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
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 [this message]
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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