Received-SPF: pass (google.com: domain of linux-kernel+bounces-10912-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:4601:e00::3 as permitted sender) client-ip=2604:1380:4601:e00::3;
Message-ID: <15b89089-3dcd-4668-8d8b-d12ff0684c29@inbox.ru>
Date: Mon, 25 Dec 2023 09:47:21 +0300
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH 1/1] riscv: set ARCH_DMA_DEFAULT_COHERENT if
 RISCV_DMA_NONCOHERENT is not set
To: Christoph Hellwig <hch@lst.de>, Jiaxun Yang <jiaxun.yang@flygoat.com>
Cc: Conor Dooley <conor@kernel.org>, linux-riscv@lists.infradead.org,
 linux-kernel@vger.kernel.org, robh@kernel.org, mpe@ellerman.id.au,
 aou@eecs.berkeley.edu, palmer@dabbelt.com, paul.walmsley@sifive.com
References: <20231221185152.327231-1-fido_max@inbox.ru>
 <20231221-discount-decade-e306e5878c46@spud>
 <f31d929c-fa0a-4046-be05-38e92afa5d92@flygoat.com>
 <20231222041428.GA2803@lst.de>
 <c53c22dd-c482-4808-bdd7-e81c01c04f9e@inbox.ru>
 <20231222-outburst-spoiling-75082a7826dd@spud>
 <be10eb21-a0ef-416e-9c0c-d53326996fba@inbox.ru>
 <7bc138f7-d5e9-471a-ae82-d6c490645623@flygoat.com>
 <6fe34090-656d-491f-8173-217d20144166@inbox.ru>
 <a25d3736-f6ca-478d-8e58-69a7c0e529f7@flygoat.com>
 <20231223045912.GA21836@lst.de>
Content-Language: en-US
From: Maxim Kochetkov <fido_max@inbox.ru>
In-Reply-To: <20231223045912.GA21836@lst.de>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit


On 23.12.2023 07:59, Christoph Hellwig wrote:
> On Fri, Dec 22, 2023 at 04:01:43PM +0000, Jiaxun Yang wrote:
>>>
>>> But arch_setup_dma_ops() is called only from of_dma_configure_id() and
>>> acpi_dma_configure_id(). So it works only for DT and ACPI devices. What
>>> about platform_device?
>>
>> Ah I see, that's the problem, in MIPS's use case all DMA capable devices
>> are following platform's default coherency. For RISC-V we assume all device
>> are enabled by ACPI or DT.
>>
>> Perhaps you can override it in driver, but that will make drivers platform
>> dependent.
>>
>> I'll leave this question to Christoph.
> 
> I've already said it.  You must not have DMA capable devices that aren't
> declared in ACPI or OF, just like on any modern Linux platform.

Ok. I've got the point. Thank you for clarification.

> 
> What devices are you concerned about anyway Maxim?

I have 3rd party external out of tree camera driver. csi, isp, dewarp 
components are OF, but common media device is created as 
platform_device. I will convert is to OF.