Re: [Question] devm_kmalloc() for DMA ?

[Lars-Peter Clausen]

On 03/08/2017 08:59 PM, Russell King - ARM Linux wrote:
> 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_*().)

On ARM. But my understanding is that this is not a universal requirement
according to DMA-API.txt. It says that mappings must be cache line aligned
and otherwise behavior is undefined.