linux-kernel - Re: [PATCH 1/1] dma: coherent: check no-map property for arm64

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Message-ID: <20210614083609.GA18701@willie-the-truck>
Date:   Mon, 14 Jun 2021 09:36:10 +0100
From:   Will Deacon <will@...nel.org>
To:     Dong Aisheng <aisheng.dong@....com>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org,
        linux-mm@...ck.org, dongas86@...il.com,
        linux-arm-kernel@...ts.infradead.org,
        Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>, catalin.marinas@....com
Subject: Re: [PATCH 1/1] dma: coherent: check no-map property for arm64

[+Catalin]

On Fri, Jun 11, 2021 at 09:10:56PM +0800, Dong Aisheng wrote:
> Coherent dma on ARM64 also can't work with mapped system ram,
> that means 'no-map' property must be specified in dts.
> Add the missing check for ARM64 platforms as well.
> Besides 'no-map' checking, 'linux,dma-default' feature is also
> enabled for ARM64 along with this patch.

Please can you explain _why_ it can't work? We don't need to tear down
aliases from the linear map for the streaming DMA API, so why is this
case different? Also, coherent devices wouldn't need this either way,
would they? What problem are you solving here?

Thanks,

Will

> 
> Cc: Christoph Hellwig <hch@....de>
> Cc: Marek Szyprowski <m.szyprowski@...sung.com>
> Cc: Robin Murphy <robin.murphy@....com>
> Signed-off-by: Dong Aisheng <aisheng.dong@....com>
> ---
>  kernel/dma/coherent.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/dma/coherent.c b/kernel/dma/coherent.c
> index 5b5b6c7ec7f2..d1831da7afba 100644
> --- a/kernel/dma/coherent.c
> +++ b/kernel/dma/coherent.c
> @@ -356,7 +356,7 @@ static int __init rmem_dma_setup(struct reserved_mem *rmem)
>  	if (of_get_flat_dt_prop(node, "reusable", NULL))
>  		return -EINVAL;
>  
> -#ifdef CONFIG_ARM
> +#if defined(CONFIG_ARM) || defined(CONFIG_ARM64)
>  	if (!of_get_flat_dt_prop(node, "no-map", NULL)) {
>  		pr_err("Reserved memory: regions without no-map are not yet supported\n");
>  		return -EINVAL;
> -- 
> 2.25.1
>