linux-kernel - Re: [PATCH 0/7] MIPS DMA coherence fixes

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Message-ID: <a46e1840-89be-de8f-6a91-3e4a16fa17c2@arm.com>
Date:   Wed, 22 Feb 2023 12:55:17 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     Christoph Hellwig <hch@....de>,
        "linux-mips@...r.kernel.org" <linux-mips@...r.kernel.org>,
        linux-kernel@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
        Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
        mpe@...erman.id.au, paul.walmsley@...ive.com, palmer@...belt.com,
        Rob Herring <robh+dt@...nel.org>, m.szyprowski@...sung.com
Subject: Re: [PATCH 0/7] MIPS DMA coherence fixes

On 2023-02-21 19:55, Jiaxun Yang wrote:
> 
> 
>> 2023年2月21日 19:46，Robin Murphy <robin.murphy@....com> 写道：
>>
>> On 2023-02-21 18:15, Jiaxun Yang wrote:
>>>> 2023年2月21日 17:54，Christoph Hellwig <hch@....de> 写道：
>>>>
>>>> Can you explain the motivation here?  Also why riscv patches are at
>>>> the end of a mips fіxes series?
>>> Ah sorry for any confusion.
>>> So the main purpose of this patch is to fix MIPS’s broken per-device coherency.
>>> To be more precise, we want to be able to control the default coherency for all devices probed from
>>> devicetree in early boot code.
>>
>> Including the patch which actually does that would be helpful. As it is, patches 4-7 here just appear to be moving an option around for no practical effect.
> 
> Well the affect is default coherency of devicetree probed devices are now following dma_default_coherent
> instead of a static Kconfig option. For MIPS platform, dma_default_coherent will be determined by boot code.

"Will be" is the issue I'm getting at. We can't review some future 
promise of a patch, we can only review actual patches. And it's hard to 
meaningfully review preparatory patches for some change without the full 
context of that change.

Thanks,
Robin.