cache coherency guidelines for DMA buffer

[naveen yadav]

apart from this you need to be aware of your cache type used in system

On Sat, Feb 8, 2014 at 8:41 PM, Miles MH Chen <orca.chen at gmail.com> wrote:
> Hi,
>
> dma_map_xxx / dma_unmap_xxx pair are used to do cache coherency.
> see Documentation/DMA-API.txt.
>
> dma_map_xxx: "Maps a piece of processor virtual memory so it can be accessed
> by the device and returns the physical handle of the memory."
> dma_unmap_xxx: "Unmaps the region previously mapped.  All the parameters
> passed in must be identical to those passed in (and returned) by the mapping
> API."
>
> Assuming you are doing DMA_TO_DEVICE synchronization:
>
> cpu accesses buffer
> dma_map_xxx  (after this point, cpu cannot touch the buffer)
> device accesses buffer
>
>
> device accesses buffer
> dma_unmap_xxx (after this point, device cannot touch the buffer)
> cpu accesses buffer
>
> Regards,
> MH
>
>
> On Sat, Feb 8, 2014 at 4:16 PM, m silverstri
> <michael.j.silverstri at gmail.com> wrote:
>>
>> Hi,
>>
>> I create DMA buffer in my kernel driver.
>> I would like to know what is  cache coherency guidelines for DMA
>> buffer referred by this post?
>>
>> http://stackoverflow.com/questions/5564326/linux-kernel-device-driver-to-dma-into-kernel-space
>>
>> Both my kernel driver and HW writes to the DMA buffer. I wnat to know
>> how to make sure  cache coherency.
>>
>> Thank you.
>>
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>
>
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