[Question] devm_kmalloc() for DMA ?

Russell King - ARM Linux linux at armlinux.org.uk
Wed Mar 8 11:59:01 PST 2017


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/
FTTC broadband for 0.8mile line: currently at 9.6Mbps down 400kbps up
according to speedtest.net.



More information about the linux-arm-kernel mailing list