From: linux@armlinux.org.uk (Russell King - ARM Linux)
To: linux-arm-kernel@lists.infradead.org
Subject: [Question] devm_kmalloc() for DMA ?
Date: Wed, 8 Mar 2017 19:59:01 +0000 [thread overview]
Message-ID: <20170308195901.GD21222@n2100.armlinux.org.uk> (raw)
In-Reply-To: <fd2097a1-c9b5-e6ab-f3b3-04b432bda0a3@metafoo.de>
On Wed, Mar 08, 2017 at 08:48:31PM +0100, Lars-Peter Clausen wrote:
> When the DMA memory is mapped for reading from the device the associated
> cachelines are invalidated without writeback. There is no guarantee that
> the changes made to the devres_node have made it to main memory yet, or
> is there?
That is incorrect.
Overlapping cache lines are always written back on transitions from CPU
to device ownership of the buffer (eg, dma_map_*().)
Updates that are made by the CPU on overlapping cache lines while the
memory is mapped for DMA may end up doing one of two things: either
overwriting the newly DMA'd data, or being lost altogether.
In the case of devm_* list manipulations, these should only ever happen
during device probe and tear down, and if DMA is active at those times,
the driver is seriously buggy.
--
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next prev parent reply other threads:[~2017-03-08 19:59 UTC|newest]
Thread overview: 11+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-03-08 10:59 [Question] devm_kmalloc() for DMA ? Masahiro Yamada
2017-03-08 11:15 ` Robin Murphy
2017-03-08 18:06 ` Masahiro Yamada
2017-03-08 19:48 ` Lars-Peter Clausen
2017-03-08 19:59 ` Russell King - ARM Linux [this message]
2017-03-08 20:44 ` Lars-Peter Clausen
2017-03-08 21:19 ` Russell King - ARM Linux
2017-03-08 21:33 ` Lars-Peter Clausen
2017-03-09 3:25 ` Masahiro Yamada
2017-03-09 9:20 ` Russell King - ARM Linux
2017-03-09 11:19 ` Robin Murphy
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