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From:   John Stultz <jstultz@google.com>
Date:   Tue, 1 Aug 2023 22:39:04 -0700
Message-ID: <CANDhNCq+3OEosUcQJ5GFgk+5OyG+JqXKM43UAo0aPz-V27OgAA@mail.gmail.com>
Subject: Re: [PATCH v2] dma-contiguous: define proper name for global cma region
To:     Christoph Hellwig <hch@lst.de>
Cc:     Pintu Agarwal <pintu.ping@gmail.com>,
        Pintu Kumar <quic_pintu@quicinc.com>,
        linux-kernel@vger.kernel.org, akpm@linux-foundation.org,
        linux-mm@kvack.org, m.szyprowski@samsung.com, robin.murphy@arm.com,
        iommu@lists.linux.dev, Sumit Semwal <sumit.semwal@linaro.org>,
        Benjamin Gaignard <benjamin.gaignard@collabora.com>,
        Liam Mark <lmark@codeaurora.org>,
        Laura Abbott <labbott@redhat.com>,
        Brian Starkey <Brian.Starkey@arm.com>,
        =?UTF-8?Q?Christian_K=C3=B6nig?= <christian.koenig@amd.com>,
        linux-media@vger.kernel.org, dri-devel@lists.freedesktop.org,
        linaro-mm-sig@lists.linaro.org
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On Tue, Aug 1, 2023 at 10:18=E2=80=AFAM Christoph Hellwig <hch@lst.de> wrot=
e:
>
> On Tue, Aug 01, 2023 at 10:42:42PM +0530, Pintu Agarwal wrote:
> > > I agree that reserved is not a very useful name.  Unfortuately the
> > > name of the region leaks to userspace through cma_heap.
> > >
> > > So I think we need prep patches to hardcode "reserved" in
> > > add_default_cma_heap first, and then remove the cma_get_name
> > > first.
> >
> > Sorry, but I could not fully understand your comments.
> > Can you please elaborate a little more what changes are required in
> > cma_heap if we change "reserved" to "global-cma-region" ?
>
> Step 1:
>
> Instead of setting exp_info.name to cma_get_name(cma);
> in __add_cma_heap just set it to "reserved", probably by passing a name
> argument.  You can also remove the unused data argument to __add_cma_heap
> and/or just fold that function into the only caller while you're at it.

So, forgive me, I've not had a chance to look into this, but my
recollection was "reserved" is the name we see on x86, but other names
are possibly provided via the dts node?

I believe on the hikey board its "linux,cma" is the name, so forcing
it to reserved would break that.

Maybe instead add a compat config option to force the cma name (so x86
can set it to "default" if needed)?

thanks
-john