linux-kernel - Re: [PATCH v2 10/11] arm64: edit zone_dma_bits to fine tune dma-direct min mask

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Date:   Mon, 26 Aug 2019 13:08:50 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     Christoph Hellwig <hch@....de>
Cc:     catalin.marinas@....com, wahrenst@....net, marc.zyngier@....com,
        robh+dt@...nel.org, Robin Murphy <robin.murphy@....com>,
        linux-arm-kernel@...ts.infradead.org, devicetree@...r.kernel.org,
        linux-arch@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-mm@...ck.org, linux-riscv@...ts.infradead.org,
        linux-kernel@...r.kernel.org, phill@...pberryi.org,
        f.fainelli@...il.com, will@...nel.org, eric@...olt.net,
        mbrugger@...e.com, linux-rpi-kernel@...ts.infradead.org,
        akpm@...ux-foundation.org, frowand.list@...il.com,
        m.szyprowski@...sung.com
Subject: Re: [PATCH v2 10/11] arm64: edit zone_dma_bits to fine tune
 dma-direct min mask

On Mon, 2019-08-26 at 09:06 +0200, Christoph Hellwig wrote:
> On Tue, Aug 20, 2019 at 04:58:18PM +0200, Nicolas Saenz Julienne wrote:
> > -	if (IS_ENABLED(CONFIG_ZONE_DMA))
> > +	if (IS_ENABLED(CONFIG_ZONE_DMA)) {
> >  		arm64_dma_phys_limit = max_zone_dma_phys();
> > +		zone_dma_bits = ilog2((arm64_dma_phys_limit - 1) &
> > GENMASK_ULL(31, 0)) + 1;
>
Hi Christoph,
thanks for the rewiews.

> This adds a way too long line.

I know, I couldn't find a way to split the operation without making it even
harder to read. I'll find a solution.

> I also find the use of GENMASK_ULL
> horribly obsfucating, but I know that opinion is't shared by everyone.

Don't have any preference so I'll happily change it. Any suggestions? Using the
explicit 0xffffffffULL seems hard to read, how about SZ_4GB - 1?


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