From: Christoph Hellwig <hch@lst.de>
To: Hillf Danton <hdanton@sina.com>
Cc: Jonas Bonn <jonas@southpole.se>,
linux-xtensa@linux-xtensa.org,
Vladimir Murzin <vladimir.murzin@arm.com>,
linux-parisc@vger.kernel.org, Vineet Gupta <vgupta@synopsys.com>,
Helge Deller <deller@gmx.de>,
linux-kernel@vger.kernel.org,
Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>,
iommu@lists.linux-foundation.org, openrisc@lists.librecores.org,
Stafford Horne <shorne@gmail.com>,
linux-snps-arc@lists.infradead.org,
Christoph Hellwig <hch@lst.de>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH 5/7] dma-direct: handle DMA_ATTR_NON_CONSISTENT in common code
Date: Tue, 25 Jun 2019 08:11:04 +0200 [thread overview]
Message-ID: <20190625061104.GB28986@lst.de> (raw)
In-Reply-To: <20190614144431.21760-6-hch@lst.de>
On Sun, Jun 16, 2019 at 06:08:40PM +0800, Hillf Danton wrote:
> Literally, any cpu (call it cpuW) other than pcx12 and pcx1 will no longer do
> dma alloc for any device with this patch applied.
Yes. And that is not a chance from the previous code, where only
pcx1 and pcx12 could do coherent allocations,
> On the other hand,
> !dev_is_dma_coherent(dev) && !(attrs & DMA_ATTR_NON_CONSISTENT) will ask
> any cpu to do dma alloc, regardless of pcx1. This patch works imo unless cpuW
> plays games only with devices that are dma coherent. I doubt it is true.
I can't parse these two sentences. But to explains the bits mentioned
here - dev_is_dma_coherent will return if a device is coherently
attached vs the cpu. This will never be true for the parisc direct
mapping. DMA_ATTR_NON_CONSISTENT asks for a non-coherent mapping that
needs to be explicitly synced. This support now is in the dma-direct
core code, and this is what the parisc specific devices used on the
non-pcxl systems use, as they do not support dma coherency at all.
(the story slightly changes when using an iommu, but that is irrelevant
here)
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next prev parent reply other threads:[~2019-06-25 6:11 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-06-14 14:44 handle "special" dma allocation in common code Christoph Hellwig
2019-06-14 14:44 ` [PATCH 1/7] arm-nommu: remove the partial DMA_ATTR_NON_CONSISTENT support Christoph Hellwig
2019-06-24 14:23 ` Vladimir Murzin
2019-06-25 6:13 ` Christoph Hellwig
2019-06-14 14:44 ` [PATCH 2/7] arc: " Christoph Hellwig
2019-06-14 14:44 ` [PATCH 3/7] openrisc: " Christoph Hellwig
2019-06-16 9:17 ` Stafford Horne
2019-06-14 14:44 ` [PATCH 4/7] dma-mapping: add a dma_alloc_need_uncached helper Christoph Hellwig
2019-06-14 14:44 ` [PATCH 5/7] dma-direct: handle DMA_ATTR_NON_CONSISTENT in common code Christoph Hellwig
2019-06-16 10:08 ` Hillf Danton
2019-06-25 6:11 ` Christoph Hellwig [this message]
2019-06-25 12:23 ` Helge Deller
2019-06-25 12:28 ` Christoph Hellwig
2019-06-14 14:44 ` [PATCH 6/7] dma-direct: handle DMA_ATTR_NO_KERNEL_MAPPING " Christoph Hellwig
2019-06-29 15:09 ` Guenter Roeck
2019-06-14 14:44 ` [PATCH 7/7] arc: use the generic remapping allocator for coherent DMA allocations Christoph Hellwig
2019-06-14 18:05 ` Eugeniy Paltsev
2019-06-15 8:35 ` hch
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