Re: DMA direct mapping fix for 5.4 and earlier stable branches

[Christoph Hellwig]

On Tue, Feb 09, 2021 at 10:23:12AM +0100, Greg KH wrote:
> >   From the view point of ZeroCopy using DMABUF, is 5.4 not 
> > mature enough, and is 5.10 enough mature ?
> >   This is the most important point for judging migration.
> 
> How do you judge "mature"?
> 
> And again, if a feature isn't present in a specific kernel version, why
> would you think that it would be a viable solution for you to use?

I'm pretty sure dma_get_sgtable has been around much longer and was
supposed to work, but only really did work properly for arm32, and
for platforms with coherent DMA.  I bet he is using non-coherent arm64,
and it would be broken for other drivers there as well if people did
test them, which they apparently so far did not.