linux-kernel - Re: [PATCH] dma-pool: Do not allocate pool memory from CMA

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Date:   Fri, 24 Jul 2020 16:36:52 +0530
From:   Amit Pundir <amit.pundir@...aro.org>
To:     Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
Cc:     Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        David Rientjes <rientjes@...gle.com>,
        linux-rpi-kernel@...ts.infradead.org, jeremy.linton@....com,
        iommu@...ts.linux-foundation.org,
        lkml <linux-kernel@...r.kernel.org>,
        John Stultz <john.stultz@...aro.org>,
        Sumit Semwal <sumit.semwal@...aro.org>
Subject: Re: [PATCH] dma-pool: Do not allocate pool memory from CMA

On Fri, 24 Jul 2020 at 15:06, Nicolas Saenz Julienne
<nsaenzjulienne@...e.de> wrote:
>
> Hi Amit,
>
> On Thu, 2020-07-23 at 10:44 +0530, Amit Pundir wrote:
> > Hi Nicolas,
> >
> > Sorry I got stuck on other things yesterday.
>
> No worries :)
>
> > On Tue, 21 Jul 2020 at 21:57, Nicolas Saenz Julienne
>
> [...]
>
> > >
> > > Let's get a bigger hammer, I'm just looking for clues here. Can you
> > > apply this and provide the dmesg output.
> > >
> > > diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
> > > index 6bc74a2d5127..2160676bf488 100644
> > > --- a/kernel/dma/pool.c
> > > +++ b/kernel/dma/pool.c
> > > @@ -268,6 +268,8 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
> > >                         schedule_work(&atomic_pool_work);
> > >         }
> > >
> > > +       dev_info(dev, "%s: size %lx, phys addr %llx, flags 0x%x\n", __func__, size, phys, flags);
> > > +
> > >         return ptr;
> > >  }
> >
> > I never made it to dma_alloc_from_pool() call from
> > dma_direct_alloc_pages(), dma_should_alloc_from_pool() returns False
> > from gfpflags_allow_blocking() block.
>
> I'm a little sceptical about this. The only way you can get memory from these
> pools is through dma_alloc_from_pool(), and given how changes in the pool
> initialization affected the phone, it's pretty clear some amount of pool
> allocation is happening.

Maybe from here iommu_dma_alloc_remap()?

I see two paths to dma_alloc_from_pool(), one from
dma_direct_alloc_pages() which I mentioned above and
2nd one is thru iommu_dma_alloc(), but the flow doesn't
reach up to dma_alloc_from_pool(), and always returns
from iommu_dma_alloc_remap().


Regards,
Amit Pundir

>
> Regards,
> Nicolas
>