linux-kernel - Re: [PATCH v2] dma-contiguous: define proper name for global cma region

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Message-ID: <CANDhNCq+3OEosUcQJ5GFgk+5OyG+JqXKM43UAo0aPz-V27OgAA@mail.gmail.com>
Date:   Tue, 1 Aug 2023 22:39:04 -0700
From:   John Stultz <jstultz@...gle.com>
To:     Christoph Hellwig <hch@....de>
Cc:     Pintu Agarwal <pintu.ping@...il.com>,
        Pintu Kumar <quic_pintu@...cinc.com>,
        linux-kernel@...r.kernel.org, akpm@...ux-foundation.org,
        linux-mm@...ck.org, m.szyprowski@...sung.com, robin.murphy@....com,
        iommu@...ts.linux.dev, Sumit Semwal <sumit.semwal@...aro.org>,
        Benjamin Gaignard <benjamin.gaignard@...labora.com>,
        Liam Mark <lmark@...eaurora.org>,
        Laura Abbott <labbott@...hat.com>,
        Brian Starkey <Brian.Starkey@....com>,
        Christian König <christian.koenig@....com>,
        linux-media@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linaro-mm-sig@...ts.linaro.org
Subject: Re: [PATCH v2] dma-contiguous: define proper name for global cma region

On Tue, Aug 1, 2023 at 10:18 AM Christoph Hellwig <hch@....de> wrote:
>
> 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