Subject: Re: [PATCH kernel 0/2] powerpc/dma: Fallback to dma_ops when persistent memory present

From: Christoph Hellwig <[email-masked]>
Date: Tue, 27 Oct 2020 09:36:47 +0100

On Wed, Oct 21, 2020 at 02:20:24PM +1100, Alexey Kardashevskiy wrote:
> This allows mixing direct DMA (to/from RAM) and
> IOMMU (to/from apersistent memory) on the PPC64/pseries
> platform. This was supposed to be a single patch but
> unexpected move of direct DMA functions happened.
> 
> This is based on sha1
> 7cf726a59435 Linus Torvalds "Merge tag 'linux-kselftest-kunit-5.10-rc1' of git://git.kernel.org/pub/scm/linux/kernel/git/shuah/linux-kselftest".
> 
> Please comment. Thanks.

I really don't like your revert.  I'm almost ready to kill of
dma-direct.h, and I really want it private in kernel/dma/, as people
keep adding abuses to drivers.

We have two options here:

 (1) duplicate the code in arch/powerpc/
 (2) add a hook to kernel/dma/

I've not been a fan of (2) in the past, but now that the code is out
of line, and we could make it dependent on a config option only set by
powerpc, I see it as the lesser evil now.