linux-kernel - Re: [PATCH] nouveau/hmm: map pages after migration

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Date:   Mon, 12 Aug 2019 12:42:30 -0700
From:   Ralph Campbell <rcampbell@...dia.com>
To:     Christoph Hellwig <hch@....de>
CC:     <linux-mm@...ck.org>, <linux-kernel@...r.kernel.org>,
        <amd-gfx@...ts.freedesktop.org>, <dri-devel@...ts.freedesktop.org>,
        <nouveau@...ts.freedesktop.org>,
        Jason Gunthorpe <jgg@...lanox.com>,
        Jérôme Glisse <jglisse@...hat.com>,
        Ben Skeggs <bskeggs@...hat.com>
Subject: Re: [PATCH] nouveau/hmm: map pages after migration


On 8/10/19 4:13 AM, Christoph Hellwig wrote:
> On something vaguely related to this patch:
> 
> You use the NVIF_VMM_PFNMAP_V0_V* defines from nvif/if000c.h, which are
> a little odd as we only ever set these bits, but they also don't seem
> to appear to be in values that are directly fed to the hardware.
> 
> On the other hand mmu/vmm.h defines a set of NVIF_VMM_PFNMAP_V0_*

Yes, I see NVKM_VMM_PFN_*

> constants with similar names and identical values, and those are used
> in mmu/vmmgp100.c and what appears to finally do the low-level dma
> mapping and talking to the hardware.  Are these two sets of constants
> supposed to be the same?  Are the actual hardware values or just a
> driver internal interface?

It looks a bit odd to me too.
I don't really know the structure/history of nouveau.
Perhaps Ben Skeggs can shed more light on your question.