Received-SPF: pass (google.com: domain of linux-kernel+bounces-9809-linux.lists.archive=gmail.com@vger.kernel.org designates 147.75.80.249 as permitted sender) client-ip=147.75.80.249;
Date: Fri, 22 Dec 2023 16:04:17 +0100
From: Christoph Hellwig <hch@lst.de>
To: Conor Dooley <conor@kernel.org>
Cc: Maxim Kochetkov <fido_max@inbox.ru>, 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
Subject: Re: [PATCH 1/1] riscv: set ARCH_DMA_DEFAULT_COHERENT if
 RISCV_DMA_NONCOHERENT is not set
Message-ID: <20231222150417.GA23363@lst.de>
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>
Precedence: bulk
MIME-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Content-Disposition: inline
In-Reply-To: <20231222-outburst-spoiling-75082a7826dd@spud>
User-Agent: Mutt/1.5.17 (2007-11-01)

On Fri, Dec 22, 2023 at 02:54:19PM +0000, Conor Dooley wrote:
> > of_dma_is_coherent() affects only DT devices. And we can override it with
> > "dma-coherent"/"dma-noncoherent". ACPI devices can specify by
> > "attr == DEV_DMA_COHERENT". But all other devices (platform_device, usb,
> 
> I would have expected that usb devices "inherit" the value from the usb
> controller whose bus they are on. Similarly, platform devices are on a
> bus that should be marked as non-coherent if that is the case.
> Christoph certainly knows better how things operate here however.

usb is not a DMAable devices, you need to use the USB layer helpers
that call the DMA API on the host controller's device.  platform_device
must have a device tree and the dma-noncoherent attribute somewhere in
the hierarchy.