Re: [PATCH 1/1] riscv: set ARCH_DMA_DEFAULT_COHERENT if RISCV_DMA_NONCOHERENT is not set

[Maxim Kochetkov]

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.