Received-SPF: pass (google.com: domain of linux-kernel+bounces-9865-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Message-ID: <be10eb21-a0ef-416e-9c0c-d53326996fba@inbox.ru>
Date: Fri, 22 Dec 2023 18:38:22 +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
Content-Language: en-US
To: Conor Dooley <conor@kernel.org>
Cc: Christoph Hellwig <hch@lst.de>, Jiaxun Yang <jiaxun.yang@flygoat.com>,
 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>
From: Maxim Kochetkov <fido_max@inbox.ru>
In-Reply-To: <20231222-outburst-spoiling-75082a7826dd@spud>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit


On 22.12.2023 17:54, Conor Dooley wrote:

>> etc..) do not have this feature. These devices will use value from
>> device_initialize(). And we have no possibility to change
>> dma_default_coherent value by disabling ARCH_DMA_DEFAULT_COHERENT.
>> Moreover, changing dma_default_coherent from false to true may cause
>> regression for other devices.
> 
> How can there be a regression when dma has been coherent by default for
> the RISC-V kernel from day 1?

Before ARCH_DMA_DEFAULT_COHERENT patch dma_default_coherent was used 
unassigned as "false" in device_initialize():
..........
#if defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_DEVICE) || \
     defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU) || \
     defined(CONFIG_ARCH_HAS_SYNC_DMA_FOR_CPU_ALL)
	dev->dma_coherent = dma_default_coherent;
#endif
..........
And now it becomes "true". It may change behavior of other non-DT drivers.