linux-kernel - Re: [RESEND][PATCH v8 0/5] DMA-BUF Heaps (destaging ION)

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Date:   Fri, 18 Oct 2019 11:33:13 -0700
From:   John Stultz <john.stultz@...aro.org>
To:     Brian Starkey <Brian.Starkey@....com>
Cc:     "Andrew F. Davis" <afd@...com>, nd <nd@....com>,
        Sudipto Paul <Sudipto.Paul@....com>,
        Vincent Donnefort <Vincent.Donnefort@....com>,
        Chenbo Feng <fengc@...gle.com>,
        Alistair Strachan <astrachan@...gle.com>,
        Liam Mark <lmark@...eaurora.org>,
        lkml <linux-kernel@...r.kernel.org>,
        Christoph Hellwig <hch@...radead.org>,
        DRI mailing list <dri-devel@...ts.freedesktop.org>,
        Hridya Valsaraju <hridya@...gle.com>,
        Ayan Halder <Ayan.Halder@....com>,
        Pratik Patel <pratikp@...eaurora.org>
Subject: Re: [RESEND][PATCH v8 0/5] DMA-BUF Heaps (destaging ION)

On Fri, Oct 18, 2019 at 2:55 AM Brian Starkey <Brian.Starkey@....com> wrote:
> On Thu, Oct 17, 2019 at 01:57:45PM -0700, John Stultz wrote:
> > On Thu, Oct 17, 2019 at 12:29 PM Andrew F. Davis <afd@...com> wrote:
> > > On 10/17/19 3:14 PM, John Stultz wrote:
> > > > But if the objection stands, do you have a proposal for an alternative
> > > > way to enumerate a subset of CMA heaps?
> > > >
> > > When in staging ION had to reach into the CMA framework as the other
> > > direction would not be allowed, so cma_for_each_area() was added. If
> > > DMA-BUF heaps is not in staging then we can do the opposite, and have
> > > the CMA framework register heaps itself using our framework. That way
> > > the CMA system could decide what areas to export or not (maybe based on
> > > a DT property or similar).
> >
> > Ok. Though the CMA core doesn't have much sense of DT details either,
> > so it would probably have to be done in the reserved_mem logic, which
> > doesn't feel right to me.
> >
> > I'd probably guess we should have some sort of dt binding to describe
> > a dmabuf cma heap and from that node link to a CMA node via a
> > memory-region phandle. Along with maybe the default heap as well? Not
> > eager to get into another binding review cycle, and I'm not sure what
> > non-DT systems will do yet, but I'll take a shot at it and iterate.
> >
> > > The end result is the same so we can make this change later (it has to
> > > come after DMA-BUF heaps is in anyway).
> >
> > Well, I'm hesitant to merge code that exposes all the CMA heaps and
> > then add patches that becomes more selective, should anyone depend on
> > the initial behavior. :/
>
> How about only auto-adding the system default CMA region (cma->name ==
> "reserved")?

Great minds... :)

> And/or the CMA auto-add could be behind a config option? It seems a
> shame to further delay this, and the CMA heap itself really is useful.

thanks
-john