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Message-ID: <aae9250e660339142e9390427a603c4cf4e282af.camel@suse.de>
Subject: Re: [PATCH v3 2/2] dma-pool: Only allocate from CMA when in same
 memory zone
From:   Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
To:     Christoph Hellwig <hch@lst.de>
Cc:     amit.pundir@linaro.org, linux-kernel@vger.kernel.org,
        Marek Szyprowski <m.szyprowski@samsung.com>,
        Robin Murphy <robin.murphy@arm.com>, rientjes@google.com,
        jeremy.linton@arm.com, linux-rpi-kernel@lists.infradead.org,
        iommu@lists.linux-foundation.org
Date:   Fri, 07 Aug 2020 10:50:19 +0200
In-Reply-To: <20200807052116.GA584@lst.de>
References: <20200806184756.32075-1-nsaenzjulienne@suse.de>
         <20200806184756.32075-3-nsaenzjulienne@suse.de>
         <20200807052116.GA584@lst.de>
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On Fri, 2020-08-07 at 07:21 +0200, Christoph Hellwig wrote:
> On Thu, Aug 06, 2020 at 08:47:55PM +0200, Nicolas Saenz Julienne wrote:
> > There is no guarantee to CMA's placement, so allocating a zone specific
> > atomic pool from CMA might return memory from a completely different
> > memory zone. To get around this double check CMA's placement before
> > allocating from it.
>=20
> As the builtbot pointed out, memblock_start_of_DRAM can't be used from
> non-__init code.  But lookig at it I think throwing that in
> is bogus anyway, as cma_get_base returns a proper physical address
> already.

It does indeed, but I'm comparing CMA's base with bitmasks that don't take =
into
account where the memory starts. Say memory starts at 0x80000000, and CMA f=
alls
into ZONE_DMA [0x80000000 0xC0000000], if you want to compare it with
DMA_BIT_MASK(zone_dma_bits) you're forced to unify the memory bases.

That said, I now realize that this doesn't work for ZONE_DMA32 which has a =
hard
limit on 32bit addresses reglardless of the memory base.

That said I still need to call memblock_start_of_DRAM() any suggestions WRT
that? I could save the value in dma_atomic_pool_init(), which is __init cod=
e.


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