Re: [Question] devm_kmalloc() for DMA ?

From	Russell King - ARM Linux <linux@armlinux.org.uk>
Newsgroups	linux.kernel
Subject	Re: [Question] devm_kmalloc() for DMA ?
Date	2017-03-08 21:20 +0100
Message-ID	<tiQdY-35t-31@gated-at.bofh.it> (permalink)
References	<tiHDI-5Js-13@gated-at.bofh.it> <tiHNo-5Nf-31@gated-at.bofh.it> <tiOc9-1K6-15@gated-at.bofh.it> <tiQdY-35t-33@gated-at.bofh.it>
Organization	linux.* mail to news gateway

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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.

-- 
RMK's Patch system: http://www.armlinux.org.uk/developer/patches/
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Thread

[Question] devm_kmalloc() for DMA ? Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-08 12:10 +0100
  Re: [Question] devm_kmalloc() for DMA ? Robin Murphy <robin.murphy@arm.com> - 2017-03-08 12:20 +0100
    Re: [Question] devm_kmalloc() for DMA ? Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-08 19:10 +0100
      Re: [Question] devm_kmalloc() for DMA ? Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-03-08 21:20 +0100
        Re: [Question] devm_kmalloc() for DMA ? Lars-Peter Clausen <lars@metafoo.de> - 2017-03-08 21:50 +0100
          Re: [Question] devm_kmalloc() for DMA ? Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-03-08 22:30 +0100
            Re: [Question] devm_kmalloc() for DMA ? Lars-Peter Clausen <lars@metafoo.de> - 2017-03-09 00:10 +0100
              Re: [Question] devm_kmalloc() for DMA ? Masahiro Yamada <yamada.masahiro@socionext.com> - 2017-03-09 04:30 +0100
                Re: [Question] devm_kmalloc() for DMA ? Russell King - ARM Linux <linux@armlinux.org.uk> - 2017-03-09 10:30 +0100
      Re: [Question] devm_kmalloc() for DMA ? Lars-Peter Clausen <lars@metafoo.de> - 2017-03-08 21:50 +0100
      Re: [Question] devm_kmalloc() for DMA ? Robin Murphy <robin.murphy@arm.com> - 2017-03-09 12:30 +0100

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