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From: Christoph Hellwig <hch@lst.de>
To: Jonathan Lemon <jonathan.lemon@gmail.com>
Cc: netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
	iommu@lists.linux-foundation.org, bpf@vger.kernel.org,
	"Björn Töpel" <bjorn.topel@intel.com>,
	"Christoph Hellwig" <hch@lst.de>,
	"Magnus Karlsson" <magnus.karlsson@intel.com>
Subject: Re: [PATCH 1/4] dma-mapping: add a new dma_need_sync API
Date: Tue, 7 Jul 2020 08:47:30 +0200	[thread overview]
Message-ID: <20200707064730.GA23602@lst.de> (raw)
In-Reply-To: <20200706194227.vfhv5o4lporxjxmq@bsd-mbp.dhcp.thefacebook.com>

On Mon, Jul 06, 2020 at 12:42:27PM -0700, Jonathan Lemon wrote:
> On Mon, Jun 29, 2020 at 03:03:56PM +0200, Christoph Hellwig wrote:
> > Add a new API to check if calls to dma_sync_single_for_{device,cpu} are
> > required for a given DMA streaming mapping.
> > 
> > +::
> > +
> > +	bool
> > +	dma_need_sync(struct device *dev, dma_addr_t dma_addr);
> > +
> > +Returns %true if dma_sync_single_for_{device,cpu} calls are required to
> > +transfer memory ownership.  Returns %false if those calls can be skipped.
> 
> Hi Christoph -
> 
> Thie call above is for a specific dma_addr.  For correctness, would I
> need to check every addr, or can I assume that for a specific memory
> type (pages returned from malloc), that the answer would be identical?

You need to check every mapping.  E.g. this API pairs with a
dma_map_single/page call.  For S/G mappings you'd need to call it for
each entry, although if you have a use case for that we really should
add a dma_sg_need_sync helper instea of open coding the scatterlist walk.
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  reply	other threads:[~2020-07-07  6:47 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-06-29 13:03 add an API to check if a streamming mapping needs sync calls Christoph Hellwig
2020-06-29 13:03 ` [PATCH 1/4] dma-mapping: add a new dma_need_sync API Christoph Hellwig
2020-07-06 19:42   ` Jonathan Lemon
2020-07-07  6:47     ` Christoph Hellwig [this message]
2020-07-07 15:11       ` Jonathan Lemon
2020-07-07 15:14         ` Christoph Hellwig
2020-06-29 13:03 ` [PATCH 2/4] xsk: replace the cheap_dma flag with a dma_need_sync flag Christoph Hellwig
2020-06-29 13:03 ` [PATCH 3/4] xsk: remove a double pool->dev assignment in xp_dma_map Christoph Hellwig
2020-06-29 13:03 ` [PATCH 4/4] xsk: use dma_need_sync instead of reimplenting it Christoph Hellwig
2020-06-29 13:39 ` add an API to check if a streamming mapping needs sync calls Björn Töpel
2020-06-29 14:22   ` Christoph Hellwig
2020-07-08  7:44   ` Christoph Hellwig
2020-07-08  9:01     ` Daniel Borkmann

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