linux-kernel - Re: [PATCH 2/3] riscv: Set dma_default

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Date:   Wed, 22 Feb 2023 14:50:36 +0000
From:   Conor Dooley <conor@...nel.org>
To:     Jiaxun Yang <jiaxun.yang@...goat.com>
Cc:     linux-mips@...r.kernel.org, linux-kernel@...r.kernel.org,
        linuxppc-dev@...ts.ozlabs.org, tsbogend@...ha.franken.de,
        mpe@...erman.id.au, paul.walmsley@...ive.com, palmer@...belt.com,
        robh+dt@...nel.org, hch@....de, m.szyprowski@...sung.com,
        robin.murphy@....com, linux-riscv@...ts.infradead.org
Subject: Re: [PATCH 2/3] riscv: Set dma_default_coherent to true

On Wed, Feb 22, 2023 at 01:37:11PM +0000, Jiaxun Yang wrote:
> For riscv our assumption is unless a device states it is non-coherent,
> we take it to be DMA coherent.
> 
> For devicetree probed devices that have been true since very begining
> with OF_DMA_DEFAULT_COHERENT selected.
> 
> Signed-off-by: Jiaxun Yang <jiaxun.yang@...goat.com>
> ---
>  arch/riscv/kernel/setup.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> index 376d2827e736..34b371180976 100644
> --- a/arch/riscv/kernel/setup.c
> +++ b/arch/riscv/kernel/setup.c
> @@ -300,6 +300,9 @@ void __init setup_arch(char **cmdline_p)
>  	riscv_init_cbom_blocksize();
>  	riscv_fill_hwcap();
>  	apply_boot_alternatives();
> +#ifdef CONFIG_RISCV_DMA_NONCOHERENT
> +	dma_default_coherent = true;
> +#endif

Do we really need to add ifdeffery for this here?
It's always coherent by default, so why do we need to say set it in
setup_arch() when we know that, regardless of options, it is true?

Cheers,
Conor.

>  	if (IS_ENABLED(CONFIG_RISCV_ISA_ZICBOM) &&
>  	    riscv_isa_extension_available(NULL, ZICBOM))
>  		riscv_noncoherent_supported();
> -- 
> 2.37.1 (Apple Git-137.1)
> 

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