On Wed, Jun 05, 2019 at 01:21:59PM +0100, Robin Murphy wrote: > And if the problem is really that you're not getting merging because of > exposing the wrong parameters to the DMA API and/or the block layer, or > that you just can't quite express your requirement to the block layer in > the first place, then that should really be tackled at the source rather > than worked around further down in the stack. The problem is that we need a way to communicate to the block layer that more than a single segment is ok IFF the DMA API instance supports merging. And of course the answer will depend on futher parameters like the maximum merged segment size and alignment for the segement. We'll need some way to communicate that, but I don't really think this is series is the way to go. We'd really need something hanging off the device (or through a query API) how the dma map ops implementation exposes under what circumstances it can merge. The driver can then communicate that to the block layer so that the block layer doesn't split requests up when reaching the segement limit.
