linux-kernel - Re: [PATCH] dma-contiguous: hornor the cma address limit setup by user

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Message-ID: <1da11218-64d4-49bc-a484-77390a5cd9bc@samsung.com>
Date: Thu, 12 Jun 2025 08:41:29 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Feng Tang <feng.tang@...ux.alibaba.com>, Robin Murphy
	<robin.murphy@....com>, Catalin Marinas <catalin.marinas@....com>, Andrew
	Morton <akpm@...ux-foundation.org>, Christoph Hellwig <hch@....de>,
	iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] dma-contiguous: hornor the cma address limit setup by
 user

On 12.06.2025 04:14, Feng Tang wrote:
> When porting a cma related usage from x86_64 server to arm64 server,
> the "cma=4G@4G" setup failed on arm64. The reason is arm64 and some
> other architectures have specific physical address limit for reserved
> cma area, like 4GB due to the device's need for 32 bit dma. Actually
> lots of platforms of those architectures don't have this device dma
> limit, but still have to obey it, and are not able to reserve a huge
> cma pool.
>
> This situation could be improved by honoring the user input cma
> physical address than the arch limit. As when users specify it, they
> already knows what the default is which probably can't suit them.
>
> Suggested-by: Robin Murphy <robin.murphy@....com>
> Signed-off-by: Feng Tang <feng.tang@...ux.alibaba.com>

Thanks, applied to dma-mapping-fixes branch.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland