linux-kernel - [PATCH] dma-contiguous: add optional cma

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Message-Id: <20220912163805.4113238-1-nate.d@variscite.com>
Date:   Mon, 12 Sep 2022 11:38:05 -0500
From:   Nate Drude <nate.d@...iscite.com>
To:     iommu@...ts.linux.dev
Cc:     Jonathan Corbet <corbet@....net>, Christoph Hellwig <hch@....de>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>,
        Borislav Petkov <bp@...e.de>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Neeraj Upadhyay <quic_neeraju@...cinc.com>,
        Randy Dunlap <rdunlap@...radead.org>,
        Damien Le Moal <damien.lemoal@...nsource.wdc.com>,
        Muchun Song <songmuchun@...edance.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        eran.m@...iscite.com, Nate Drude <nate.d@...iscite.com>
Subject: [PATCH] dma-contiguous: add optional cma_name for cma= kernel parameter

When cma is defined in the device tree, the device tree node
name is used as the cma name. In the following example, the cma
will be named 'linux,cma':

linux,cma {
	compatible = "shared-dma-pool";
	reusable;
	size = <0 0x3c000000>;
	alloc-ranges = <0 0x40000000 0 0xC0000000>;
	linux,cma-default;
};

And a device /dev/dma_heap/linux,cma is created.

However, when cma is provided by command line, a default
name of 'reserved' is used, and the device path changes to
/dev/dma_heap/reserved.

This is problematic because some user space applications,
like gstreamer plugins, are expecting /dev/dma_heap/linux,cma.

This parameter allows overriding the default 'reserved' name.

Signed-off-by: Nate Drude <nate.d@...iscite.com>
---
 .../admin-guide/kernel-parameters.txt         |  7 +++++++
 kernel/dma/contiguous.c                       | 21 ++++++++++++++++++-
 2 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
index 51397a320f5e..975ec862d071 100644
--- a/Documentation/admin-guide/kernel-parameters.txt
+++ b/Documentation/admin-guide/kernel-parameters.txt
@@ -644,6 +644,13 @@
 			altogether. For more information, see
 			kernel/dma/contiguous.c
 
+	cma_name=	Override the cma heap name
+			Format: <string>
+			When passing the cma kernel parameter, the default
+			cma name is 'reserved'. This parameter allows it to
+			be overriden to align with the device tree name,
+			like 'linux,cma'.
+
 	cma_pernuma=nn[MG]
 			[ARM64,KNL,CMA]
 			Sets the size of kernel per-numa memory area for
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index 3d63d91cba5c..e89819ec183e 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -74,6 +74,7 @@ static const phys_addr_t size_bytes __initconst =
 static phys_addr_t  size_cmdline __initdata = -1;
 static phys_addr_t base_cmdline __initdata;
 static phys_addr_t limit_cmdline __initdata;
+static char name_cmdline[CMA_MAX_NAME] = "reserved";
 
 static int __init early_cma(char *p)
 {
@@ -96,6 +97,24 @@ static int __init early_cma(char *p)
 }
 early_param("cma", early_cma);
 
+static int __init early_cma_name(char *p)
+{
+	if (!p) {
+		pr_err("Config string not provided\n");
+		return -EINVAL;
+	}
+
+	if (!strlen(p)) {
+		pr_err("cma_name must have at least one character\n");
+		return -EINVAL;
+	}
+
+	snprintf(name_cmdline, CMA_MAX_NAME, p);
+
+	return 0;
+}
+early_param("cma_name", early_cma_name);
+
 #ifdef CONFIG_DMA_PERNUMA_CMA
 
 static struct cma *dma_contiguous_pernuma_area[MAX_NUMNODES];
@@ -231,7 +250,7 @@ int __init dma_contiguous_reserve_area(phys_addr_t size, phys_addr_t base,
 	int ret;
 
 	ret = cma_declare_contiguous(base, size, limit, 0, 0, fixed,
-					"reserved", res_cma);
+					name_cmdline, res_cma);
 	if (ret)
 		return ret;
 
-- 
2.37.3