Message-ID: <a46e1840-89be-de8f-6a91-3e4a16fa17c2@arm.com>
Date:   Wed, 22 Feb 2023 12:55:17 +0000
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Subject: Re: [PATCH 0/7] MIPS DMA coherence fixes
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To:     Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc:     Christoph Hellwig <hch@lst.de>,
        "linux-mips@vger.kernel.org" <linux-mips@vger.kernel.org>,
        linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org,
        Thomas Bogendoerfer <tsbogend@alpha.franken.de>,
        mpe@ellerman.id.au, paul.walmsley@sifive.com, palmer@dabbelt.com,
        Rob Herring <robh+dt@kernel.org>, m.szyprowski@samsung.com
References: <20230221124613.2859-1-jiaxun.yang@flygoat.com>
 <20230221175423.GA15247@lst.de>
 <A8AC22A0-E883-4D9B-A629-5A3721B976C5@flygoat.com>
 <ed2d7750-786d-82a1-5e79-1f216a682b20@arm.com>
 <34578218-DC7A-4C8B-A01A-AD64831CCB43@flygoat.com>
From:   Robin Murphy <robin.murphy@arm.com>
In-Reply-To: <34578218-DC7A-4C8B-A01A-AD64831CCB43@flygoat.com>
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On 2023-02-21 19:55, Jiaxun Yang wrote:
> 
> 
>> 2023年2月21日 19:46，Robin Murphy <robin.murphy@arm.com> 写道：
>>
>> On 2023-02-21 18:15, Jiaxun Yang wrote:
>>>> 2023年2月21日 17:54，Christoph Hellwig <hch@lst.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.