linux-kernel - Re: [PATCH v2 RFC/RFT 1/5] ARM: dma-mapping: Add fallback normal page allocations

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Date:   Wed, 24 Apr 2019 12:38:41 -0700
From:   Nicolin Chen <nicoleotsuka@...il.com>
To:     Christoph Hellwig <hch@....de>
Cc:     robin.murphy@....com, vdumpa@...dia.com, linux@...linux.org.uk,
        catalin.marinas@....com, will.deacon@....com, joro@...tes.org,
        m.szyprowski@...sung.com, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org, iommu@...ts.linux-foundation.org,
        tony@...mide.com
Subject: Re: [PATCH v2 RFC/RFT 1/5] ARM: dma-mapping: Add fallback normal
 page allocations

On Wed, Apr 24, 2019 at 09:26:52PM +0200, Christoph Hellwig wrote:
> On Wed, Apr 24, 2019 at 11:33:11AM -0700, Nicolin Chen wrote:
> > I feel it's similar to my previous set, which did most of these
> > internally except the renaming part. But Catalin had a concern
> > that some platforms might have limits on CMA range [1]. Will it
> > be still okay to do the fallback internally?
> > 
> > [1: https://www.spinics.net/lists/arm-kernel/msg714295.html ]
> 
> Catalins statement is correct, but I don't see how it applies to
> your patch.  Your patch just ensures that the fallback we have
> in most callers is uniformly applied everywhere.  The non-iommu
> callers will still need to select a specific zone and/or retry
> just the page allocator with other flags if the CMA (or fallback)
> page doesn't match what they need.  dma-direct does this correctly
> and I think the arm32 allocator does as well, although it is a bit
> hard to follow sometimes.

Okay. I will revise and submit the patches then. I think we
can still discuss on this topic once we have the changes.

Thanks