linux-kernel - Re: [PATCH v4 3/4] arm64: use both ZONE_DMA and ZONE

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Date:   Mon, 09 Sep 2019 10:46:39 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Catalin Marinas <catalin.marinas@....com>
Cc:     f.fainelli@...il.com, mbrugger@...e.com, marc.zyngier@....com,
        robin.murphy@....com, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, robh+dt@...nel.org, wahrenst@....net,
        m.szyprowski@...sung.com, linux-riscv@...ts.infradead.org,
        phill@...pberrypi.org, Will Deacon <will@...nel.org>, hch@....de,
        linux-arm-kernel@...ts.infradead.org,
        linux-rpi-kernel@...ts.infradead.org
Subject: Re: [PATCH v4 3/4] arm64: use both ZONE_DMA and ZONE_DMA32

On Sun, 2019-09-08 at 22:27 +0100, Catalin Marinas wrote:
> On Fri, Sep 06, 2019 at 02:06:14PM +0200, Nicolas Saenz Julienne wrote:
> > @@ -430,7 +454,7 @@ void __init arm64_memblock_init(void)
> >  
> >  	high_memory = __va(memblock_end_of_DRAM() - 1) + 1;
> >  
> > -	dma_contiguous_reserve(arm64_dma32_phys_limit);
> > +	dma_contiguous_reserve(arm64_dma_phys_limit ? : arm64_dma32_phys_limit);
> >  }
> >  
> >  void __init bootmem_init(void)
> > @@ -534,6 +558,7 @@ static void __init free_unused_memmap(void)
> >  void __init mem_init(void)
> >  {
> >  	if (swiotlb_force == SWIOTLB_FORCE ||
> > +	    max_pfn > (arm64_dma_phys_limit >> PAGE_SHIFT) ||
> >  	    max_pfn > (arm64_dma32_phys_limit >> PAGE_SHIFT))
> >  		swiotlb_init(1);
> 
> So here we want to initialise the swiotlb only if we need bounce
> buffers. Prior to this patch, we assumed that swiotlb is needed if
> max_pfn is beyond the reach of 32-bit devices. With ZONE_DMA, we need to
> lower this limit to arm64_dma_phys_limit.
>
> If ZONE_DMA is enabled, just comparing max_pfn with arm64_dma_phys_limit
> is sufficient since the dma32 one limit always higher. However, if
> ZONE_DMA is disabled, arm64_dma_phys_limit is 0, so we may initialise
> swiotlb unnecessarily. I guess you need a similar check to the
> dma_contiguous_reserve() above.

Of course.

> 
> With that:
> 
> Reviewed-by: Catalin Marinas <catalin.marinas@....com>
> 
> Unless there are other objections, I can queue this series for 5.5 in a
> few weeks time (too late for 5.4).

Thanks!


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