linux-kernel - Re: [PATCH v6 2/2] dma-buf: heaps: cma: Create CMA heap for each CMA reserved region

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Message-ID: <6045bcfb-35ef-410b-bd7c-0ca7c5c589c4@ti.com>
Date: Wed, 9 Jul 2025 11:14:37 -0500
From: Andrew Davis <afd@...com>
To: Maxime Ripard <mripard@...nel.org>, Rob Herring <robh@...nel.org>,
        Saravana Kannan <saravanak@...gle.com>,
        Sumit Semwal
	<sumit.semwal@...aro.org>,
        Benjamin Gaignard
	<benjamin.gaignard@...labora.com>,
        Brian Starkey <Brian.Starkey@....com>,
        John Stultz <jstultz@...gle.com>,
        "T.J. Mercier" <tjmercier@...gle.com>,
        Christian König <christian.koenig@....com>,
        Krzysztof
 Kozlowski <krzk+dt@...nel.org>,
        Conor Dooley <conor+dt@...nel.org>,
        Marek
 Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>
CC: Jared Kangas <jkangas@...hat.com>,
        Mattijs Korpershoek
	<mkorpershoek@...nel.org>,
        <devicetree@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-media@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        <linaro-mm-sig@...ts.linaro.org>, <iommu@...ts.linux.dev>
Subject: Re: [PATCH v6 2/2] dma-buf: heaps: cma: Create CMA heap for each CMA
 reserved region

On 7/9/25 7:44 AM, Maxime Ripard wrote:
> Aside from the main CMA region, it can be useful to allow userspace to
> allocate from the other CMA reserved regions.
> 
> Indeed, those regions can have specific properties that can be useful to
> a specific us-case.
> 
> For example, one of them platform I've been with has ECC enabled on the
> entire memory but for a specific region. Using that region to allocate
> framebuffers can be particular beneficial because enabling the ECC has a
> performance and memory footprint cost.
> 
> Thus, exposing these regions as heaps user-space can allocate from and
> import wherever needed allows to cover that use-case.
> 
> For now, only shared-dma-pools regions with the reusable property (ie,
> backed by CMA) are supported, but eventually we'll want to support other
> DMA pools types.
> 
> Signed-off-by: Maxime Ripard <mripard@...nel.org>
> ---
>   drivers/dma-buf/heaps/cma_heap.c | 52 +++++++++++++++++++++++++++++++++++++++-
>   1 file changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/dma-buf/heaps/cma_heap.c b/drivers/dma-buf/heaps/cma_heap.c
> index 0df007111975447d555714d61ead9699287fd65a..31a18683ee25788a800f3f878fd958718a930ff7 100644
> --- a/drivers/dma-buf/heaps/cma_heap.c
> +++ b/drivers/dma-buf/heaps/cma_heap.c
> @@ -19,10 +19,12 @@
>   #include <linux/err.h>
>   #include <linux/highmem.h>
>   #include <linux/io.h>
>   #include <linux/mm.h>
>   #include <linux/module.h>
> +#include <linux/of.h>
> +#include <linux/of_reserved_mem.h>
>   #include <linux/scatterlist.h>
>   #include <linux/slab.h>
>   #include <linux/vmalloc.h>
>   
>   #define DEFAULT_CMA_NAME "default_cma_region"
> @@ -421,7 +423,55 @@ static int __init add_default_cma_heap(void)
>   				ERR_PTR(ret));
>   	}
>   
>   	return 0;
>   }
> -module_init(add_default_cma_heap);
> +
> +static int __init add_cma_heaps(void)
> +{
> +	struct device_node *rmem_node;
> +	struct device_node *node;
> +	int ret;
> +
> +	ret = add_default_cma_heap();

Will this double add the default CMA region if it was declared
using DT (reserved-memory) when all those nodes are again scanned
through below? Might need a check in that loop for linux,cma-default.

> +	if (ret)
> +		return ret;
> +
> +	rmem_node = of_find_node_by_path("/reserved-memory");
> +	if (!rmem_node)
> +		goto out;

Can just return here, "out" path doesn't need to put a NULL node.

Andrew

> +
> +	for_each_child_of_node(rmem_node, node) {
> +		struct reserved_mem *rmem;
> +		struct cma *cma;
> +
> +		rmem = of_reserved_mem_lookup(node);
> +		if (!rmem) {
> +			ret = -EINVAL;
> +			goto err_put_node;
> +		}
> +
> +		if (!of_reserved_mem_is_contiguous(rmem))
> +			continue;
> +
> +		cma = rmem->priv;
> +		if (!cma) {
> +			ret = -EINVAL;
> +			goto err_put_node;
> +		}
> +
> +		ret = __add_cma_heap(cma, of_node_full_name(node));
> +		if (ret)
> +			goto err_put_node;
> +	}
> +
> +out:
> +	of_node_put(rmem_node);
> +	return 0;
> +
> +err_put_node:
> +	of_node_put(rmem_node);
> +	return ret;
> +}
> +
> +module_init(add_cma_heaps);
>   MODULE_DESCRIPTION("DMA-BUF CMA Heap");
>