linux-kernel - Re: [PATCH -fixes] dma-mapping: add default implementation to arch_dma_{set|clear}

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Message-ID: <tencent_651BC4D11C9730062064ACB186AF4A904005@qq.com>
Date: Tue, 9 Jul 2024 19:39:29 +0800
From: Yangyu Chen <cyy@...self.name>
To: Christoph Hellwig <hch@....de>
Cc: iommu@...ts.linux.dev,
 Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
 Marek Szyprowski <m.szyprowski@...sung.com>,
 Robin Murphy <robin.murphy@....com>
Subject: Re: [PATCH -fixes] dma-mapping: add default implementation to
 arch_dma_{set|clear}_uncached



> On Jul 9, 2024, at 19:19, Christoph Hellwig <hch@....de> wrote:
> 
> On Tue, Jul 09, 2024 at 05:25:29PM +0800, Yangyu Chen wrote:
>> Currently, we have some code in kernel/dma/direct.c which references
>> arch_dma_set_uncached and arch_dma_clear_uncached. However, many
>> architectures do not provide these symbols, and the code currently
>> relies on compiler optimization to cut the unnecessary code. When the
>> compiler fails to optimize it, the code will reference the symbol and
>> cause a link error. I found this bug when developing some new extensions
>> for RISC-V on LLVM. The error message is shown below:
> 
> Same comment as for the last one.  I think your compiler misbehaves,
> and the typical reason for that would be if you disable all
> optimizations.
> 

The reason is that some optimizations failed to apply after adding
some passes. I will fix the compiler later. Whatever, we should not
rely on this optimization to get the code being successfully compiled.