From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Russell King - ARM Linux <linux@arm.linux.org.uk>
Cc: David Woodhouse <dwmw2@infradead.org>,
Brian Norris <computersforpeace@gmail.com>,
linux-mtd@lists.infradead.org,
Andrew Morton <akpm@linux-foundation.org>,
Dave Gordon <david.s.gordon@intel.com>,
linux-crypto@vger.kernel.org,
Herbert Xu <herbert@gondor.apana.org.au>,
Vinod Koul <vinod.koul@intel.com>,
Richard Weinberger <richard@nod.at>,
Joerg Roedel <joro@8bytes.org>,
linux-kernel@vger.kernel.org, linux-spi@vger.kernel.org,
Vignesh R <vigneshr@ti.com>,
linux-mm@kvack.org, iommu@lists.linux-foundation.org,
Mark Brown <broonie@kernel.org>,
Hans Verkuil <hans.verkuil@cisco.com>,
Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
dmaengine@vger.kernel.org,
Dan Williams <dan.j.williams@intel.com>,
linux-media@vger.kernel.org,
"David S. Miller" <davem@davemloft.net>,
linux-arm-kernel@lists.infradead.org,
Mauro Carvalho Chehab <m.chehab@samsung.com>
Subject: Re: [PATCH 2/4] scatterlist: add sg_alloc_table_from_buf() helper
Date: Thu, 31 Mar 2016 16:45:57 +0200 [thread overview]
Message-ID: <20160331164557.544ed780@bbrezillon> (raw)
In-Reply-To: <20160331141412.GK19428@n2100.arm.linux.org.uk>
Hi Russell,
On Thu, 31 Mar 2016 15:14:13 +0100
Russell King - ARM Linux <linux@arm.linux.org.uk> wrote:
> On Thu, Mar 31, 2016 at 02:29:42PM +0200, Boris Brezillon wrote:
> > sg_alloc_table_from_buf() provides an easy solution to create an sg_table
> > from a virtual address pointer. This function takes care of dealing with
> > vmallocated buffers, buffer alignment, or DMA engine limitations (maximum
> > DMA transfer size).
>
> Please note that the DMA API does not take account of coherency of memory
> regions other than non-high/lowmem - there are specific extensions to
> deal with this.
Ok, you said 'non-high/lowmem', this means vmalloced and kmapped buffers
already fall in this case, right?
Could you tell me more about those specific extensions?
>
> What this means is that having an API that takes any virtual address
> pointer, converts it to a scatterlist which is then DMA mapped, is
> unsafe.
Which means some implementations already get this wrong (see
spi_map_buf(), and I'm pretty sure it's not the only one).
>
> It'll be okay for PIPT and non-aliasing VIPT cache architectures, but
> for other cache architectures this will hide this problem and make
> review harder.
>
Ok, you lost me. I'll have to do my homework and try to understand what
this means :).
Thanks for your valuable inputs.
Best Regards,
Boris
--
Boris Brezillon, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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next prev parent reply other threads:[~2016-03-31 14:46 UTC|newest]
Thread overview: 12+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-03-31 12:29 [PATCH 0/4] scatterlist: sg_table from virtual pointer Boris Brezillon
2016-03-31 12:29 ` [PATCH 1/4] mm: add is_highmem_addr() helper Boris Brezillon
2016-04-04 8:14 ` Vignesh R
2016-04-04 15:05 ` Boris Brezillon
2016-03-31 12:29 ` [PATCH 2/4] scatterlist: add sg_alloc_table_from_buf() helper Boris Brezillon
2016-03-31 14:14 ` Russell King - ARM Linux
2016-03-31 14:45 ` Boris Brezillon [this message]
2016-03-31 15:09 ` Russell King - ARM Linux
2016-03-31 12:29 ` [PATCH 3/4] spi: use sg_alloc_table_from_buf() Boris Brezillon
2016-03-31 17:23 ` Mark Brown
2016-03-31 12:29 ` [PATCH 4/4] mtd: provide helper to prepare buffers for DMA operations Boris Brezillon
2016-04-01 3:13 ` kbuild test robot
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