linux-kernel - Re: [PATCH 5/5] mm, hmm: mark hmm_devmem_{add, add_resource} EXPORT_SYMBOL

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Date:   Tue, 5 Jun 2018 14:24:38 -0400
From:   Jerome Glisse <jglisse@...hat.com>
To:     Andrew Morton <akpm@...ux-foundation.org>
Cc:     Christoph Hellwig <hch@....de>,
        Dan Williams <dan.j.williams@...el.com>,
        Logan Gunthorpe <logang@...tatee.com>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/5] mm, hmm: mark hmm_devmem_{add, add_resource}
 EXPORT_SYMBOL_GPL

On Tue, May 22, 2018 at 02:31:21PM -0700, Andrew Morton wrote:
> On Tue, 22 May 2018 08:32:36 +0200 Christoph Hellwig <hch@....de> wrote:
> 
> > On Mon, May 21, 2018 at 03:35:40PM -0700, Dan Williams wrote:
> > > The routines hmm_devmem_add(), and hmm_devmem_add_resource() are small
> > > wrappers around devm_memremap_pages(). The devm_memremap_pages()
> > > interface is a subset of the hmm functionality which has more and deeper
> > > ties into the kernel memory management implementation. It was an
> > > oversight that these symbols were not marked EXPORT_SYMBOL_GPL from the
> > > outset due to how they originally copied (and now reuse)
> > > devm_memremap_pages().
> > 
> > If we end up keeping this code: absolutely.  Then again I think without
> > an actual user this should have never been merged, and should be removed
> > until one shows up.
> > 
> 
> It wasn't simple.  Quite a lot of manufacturers were (are?) developing
> quite complex driver code which utilizes hmm.  Merging hmm to give a
> stable target for that development and in the expectation that those
> things would be coming along was a risk and I don't think we yet know
> the outcome.
> 
> Jerome, are you able to provide any updates on all of this?

Sorry for taking so long to reply to this, I am just back from vacation.

I posted a v1 for nouveau to use HMM back in April or early May. I want
to post a v2 soon in June. For it to get upstream it needs to fullfill
linux drm sub-system requirement which are an open source userspace for
any functionality added to GPU driver. Work for this have been going
on for a while too and userspace bits are slowly getting upstream inside
Mesa. I need to sync up to see what is still missing in Mesa.

So i won't be able to get nouveau HMM bits merge before the userspace
bits are merge too. I was hopping for 4.18 but more likely 4.19.

I know HMM have been a big chicken and egg thing and that timing for
the egg did not match the timing for the chicken :) But it is getting
there.

Also I expect more hardware and associated upstream driver to make use
of HMM but i can not comment further on that at this time because of
NDA.

Cheers,
Jérôme