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

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Message-ID: <20191018185723.GA27993@arm.com>
Date:   Fri, 18 Oct 2019 18:57:24 +0000
From:   Ayan Halder <Ayan.Halder@....com>
To:     John Stultz <john.stultz@...aro.org>
CC:     Brian Starkey <Brian.Starkey@....com>,
        "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>,
        Pratik Patel <pratikp@...eaurora.org>
Subject: Re: [RESEND][PATCH v8 0/5] DMA-BUF Heaps (destaging ION)

On Fri, Oct 18, 2019 at 11:49:22AM -0700, John Stultz wrote:
> On Fri, Oct 18, 2019 at 11:41 AM Ayan Halder <Ayan.Halder@....com> wrote:
> > On Fri, Oct 18, 2019 at 09:55:17AM +0000, Brian Starkey 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")?
> > >
> > > 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.
> > >
> > A bit of a detour, comming back to the issue why the following node
> > was not getting detected by the dma-buf heaps framework.
> >
> >         reserved-memory {
> >                 #address-cells = <2>;
> >                 #size-cells = <2>;
> >                 ranges;
> >
> >                 display_reserved: framebuffer@...00000 {
> >                         compatible = "shared-dma-pool";
> >                         linux,cma-default;
> >                         reusable; <<<<<<<<<<<<-----------This was missing in our
> > earlier node
> >                         reg = <0 0x60000000 0 0x08000000>;
> >                 };
> 
> Right. It has to be a CMA region for us to expose it from the cma heap.
> 
> 
> > With 'reusable', rmem_cma_setup() succeeds , but the kernel crashes as follows :-
> >
> > [    0.450562] WARNING: CPU: 2 PID: 1 at mm/cma.c:110 cma_init_reserved_areas+0xec/0x22c
> 
> Is the value 0x60000000 you're using something you just guessed at? It
> seems like the warning here is saying the pfn calculated from the base
> address isn't valid.
It is a valid memory region we use to allocate framebuffers.
> 
> thanks
> -john