linux-kernel - Re: [PATCH v3] dma-coherent: add support for multi coherent rmems per dev

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Date: Fri, 23 Feb 2024 07:37:23 +0100
From: Christoph Hellwig <hch@....de>
To: Howard Yen <howardyen@...gle.com>
Cc: Christoph Hellwig <hch@....de>, m.szyprowski@...sung.com,
	robin.murphy@....com, gregkh@...uxfoundation.org,
	andriy.shevchenko@...ux.intel.com, rafael@...nel.org,
	broonie@...nel.org, james@...iv.tech, james.clark@....com,
	masahiroy@...nel.org, linux-kernel@...r.kernel.org,
	iommu@...ts.linux.dev
Subject: Re: [PATCH v3] dma-coherent: add support for multi coherent rmems
 per dev

On Wed, Feb 21, 2024 at 05:27:58PM +0800, Howard Yen wrote:
> The reason why I tried to propose this patch is that in the system I'm
> working on, where the driver utilizes the coherent reserved memory in
> the subsystem for DMA, which has limited memory space as its primary
> usage. During the execution of the driver, there is a possibility of
> encountering memory depletion scenarios with the primary one.
> 
> To address this issue, I tried to create a patch that enables the
> coherent reserved memory driver to support multiple coherent reserved
> memory regions per device. This modification aims to provide the
> driver with the ability to search for memory from a secondary region
> if the primary memory is exhausted, and so on.

This all seems pretty vague.  Can you point to your driver submission
and explain why it can't just use a larger region instead of multiple
smaller ones?