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

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Message-ID: <20191018095516.inwes5avdeixl5nr@DESKTOP-E1NTVVP.localdomain>
Date:   Fri, 18 Oct 2019 09:55:17 +0000
From:   Brian Starkey <Brian.Starkey@....com>
To:     John Stultz <john.stultz@...aro.org>
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 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")?

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.

Cheers,
-Brian

> 
> So, <sigh>, I'll start on the rework for the CMA bits.
> 
> That said, I'm definitely wanting to make some progress on this patch
> series, so maybe we can still merge the core/helpers/system heap and
> just hold the cma heap for a rework on the enumeration bits. That way
> we can at least get other folks working on switching their vendor
> heaps from ION.
> 
> Sumit: Does that sound ok? Assuming no other objections, can you take
> the v11 set minus the CMA heap patch?
> 
> thanks
> -john