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 <[email protected]>
---
.../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
On 2022-09-12 17:38, Nate Drude wrote:
> 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.
If userspace expects the CMA heap driver to expose a consistent name for
CMA heaps, shouldn't it be the CMA heap driver's responsibility to
expose a consistent name for CMA heaps? Tinkering with the core CMA code
doesn't feel like the right approach.
Furthermore, given that DT reserved-memory nodes carrying the
"linux-cma-default" property equally can (and do) have different names
as well, that or fixing userspace really are the only robust options.
Thanks,
Robin.
> 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 <[email protected]>
> ---
> .../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;
>
On Tue, Sep 13, 2022 at 11:45:17AM +0100, Robin Murphy wrote:
> If userspace expects the CMA heap driver to expose a consistent name for
> CMA heaps, shouldn't it be the CMA heap driver's responsibility to expose a
> consistent name for CMA heaps? Tinkering with the core CMA code doesn't
> feel like the right approach.
Agreed. In fact I think exposing this name in a uapi seems like a really
bad idea that is asking for a lot of trouble.