linux-kernel - Re: [PATCH v3 2/3] dma-mapping: replace zone_dma_bits by zone_dma

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Message-ID: <20240730153450.GA30021@lst.de>
Date: Tue, 30 Jul 2024 17:34:50 +0200
From: Christoph Hellwig <hch@....de>
To: Nathan Chancellor <nathan@...nel.org>
Cc: kernel test robot <lkp@...el.com>, Baruch Siach <baruch@...s.co.il>,
	Christoph Hellwig <hch@....de>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>, llvm@...ts.linux.dev,
	oe-kbuild-all@...ts.linux.dev, linux-s390@...r.kernel.org,
	Ramon Fried <ramon@...reality.ai>,
	Petr Tesařík <petr@...arici.cz>,
	Robin Murphy <robin.murphy@....com>, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev, Elad Nachman <enachman@...vell.com>,
	linuxppc-dev@...ts.ozlabs.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v3 2/3] dma-mapping: replace zone_dma_bits by
 zone_dma_limit

On Mon, Jul 29, 2024 at 07:12:08PM -0700, Nathan Chancellor wrote:
> >          |             ~~~~~~~~~~~~~~                   ^~~~~~~~~~~~~~~~
> >    include/linux/dma-mapping.h:77:40: note: expanded from macro 'DMA_BIT_MASK'
> >       77 | #define DMA_BIT_MASK(n) (((n) == 64) ? ~0ULL : ((1ULL<<(n))-1))
> >          |                                        ^~~~~
> >    2 warnings generated.
> 
> FWIW, this is likely a false positive due to an issue in Clang with the
> control flow graph for global variables:
> 
> https://github.com/ClangBuiltLinux/linux/issues/92
> 
> DMA_BIT_MASK() has been the biggest offender :/ If there is any way to
> refactor this code to avoid this, that would be great (as that has been
> one of our longest outstanding issues and getting it fixed in the
> compiler does not seem super easy at this point).

I have no idea what you'd want changed here, but I'll happily take
patches.