Re: [PATCH] swiotlb: sync buffer when mapping FROM_DEVICE

[Horia Geanta]

On 5/23/2019 7:43 PM, Christoph Hellwig wrote:
> On Thu, May 23, 2019 at 07:35:07AM +0200, Marek Szyprowski wrote:
>> Don't we have DMA_BIDIRECTIONAL for such case?
> 
> Not sure if it was intended for that case, but it definitively should
> do the right thing for swiotlb, and it should also do the right thing
> in terms of cache maintainance.
> 
>> Maybe we should update 
>> documentation a bit to point that DMA_FROM_DEVICE expects the whole 
>> buffer to be filled by the device?
> 
> Probably. Horia, can you try to use DMA_BIDIRECTIONAL?
> 
This works, but at the cost of performance - all the cache lines being written
back to memory, just to be overwritten by the device.

Thanks,
Horia