linux-kernel - Re: [PATCH 16/33] powerpc/powernv: remove dead npu-dma code

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Date:   Mon, 15 Oct 2018 13:45:26 +1100
From:   Benjamin Herrenschmidt <benh@...nel.crashing.org>
To:     Alexey Kardashevskiy <aik@...abs.ru>,
        Christoph Hellwig <hch@....de>,
        Paul Mackerras <paulus@...ba.org>,
        Michael Ellerman <mpe@...erman.id.au>
Cc:     linuxppc-dev@...ts.ozlabs.org, iommu@...ts.linux-foundation.org,
        linux-mm@...ck.org, linux-arch@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/33] powerpc/powernv: remove dead npu-dma code

On Mon, 2018-10-15 at 12:34 +1100, Alexey Kardashevskiy wrote:
> On 10/10/2018 00:24, Christoph Hellwig wrote:
> > This code has been unused since it was merged and is in the way of
> > cleaning up the DMA code, thus remove it.
> > 
> > This effectively reverts commit 5d2aa710 ("powerpc/powernv: Add support
> > for Nvlink NPUs").
> 
> 
> This code is heavily used by the NVIDIA GPU driver.

Some of it is, yes. And while I don't want to be involved in the
discussion about that specific can of worms, there is code in this file
related to the custom "always error" DMA ops that I suppose we could
remove, which is what is getting in the way of Christoph cleanups. It's
just meant as a debug stuff to catch incorrect attempts at doing the
dma mappings on the wrong "side" of the GPU.

Cheers,
Ben.