From: Christoph Hellwig <hch@lst.de>
To: Hillf Danton <hdanton@sina.com>
Cc: Christoph Hellwig <hch@lst.de>,
Vineet Gupta <vgupta@synopsys.com>,
Jonas Bonn <jonas@southpole.se>,
Stefan Kristiansson <stefan.kristiansson@saunalahti.fi>,
Stafford Horne <shorne@gmail.com>, Helge Deller <deller@gmx.de>,
Vladimir Murzin <vladimir.murzin@arm.com>,
linux-snps-arc@lists.infradead.org,
linux-arm-kernel@lists.infradead.org,
openrisc@lists.librecores.org, linux-parisc@vger.kernel.org,
linux-xtensa@linux-xtensa.org, iommu@lists.linux-foundation.org,
linux-kernel@vger.kernel.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)
next prev parent reply other threads:[~2019-06-25 6:11 UTC|newest]
Thread overview: 17+ 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
2019-06-25 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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