[PATCH] of: reserved_mem: Allow reserved_mem framework detect "cma=" kernel param

[PATCH] of: reserved_mem: Allow reserved_mem framework detect "cma=" kernel param

[Oreoluwa Babatunde]

When initializing the default cma region, the "cma=" kernel parameter
takes priority over a DT defined linux,cma-default region. Hence, give
the reserved_mem framework the ability to detect this so that the DT
defined cma region can skip initialization accordingly.

Signed-off-by: Oreoluwa Babatunde <oreoluwa.babatunde@oss.qualcomm.com>
---
 drivers/of/of_reserved_mem.c | 19 +++++++++++++++++--
 include/linux/cma.h          |  1 +
 kernel/dma/contiguous.c      | 16 ++++++++++------
 3 files changed, 28 insertions(+), 8 deletions(-)

diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
index 2e9ea751ed2d..bef68a4916b5 100644
--- a/drivers/of/of_reserved_mem.c
+++ b/drivers/of/of_reserved_mem.c
@@ -158,7 +158,7 @@ static int __init __reserved_mem_reserve_reg(unsigned long node,
 	phys_addr_t base, size;
 	int len;
 	const __be32 *prop;
-	bool nomap;
+	bool nomap, default_cma;
 
 	prop = of_get_flat_dt_prop(node, "reg", &len);
 	if (!prop)
@@ -171,6 +171,12 @@ static int __init __reserved_mem_reserve_reg(unsigned long node,
 	}
 
 	nomap = of_get_flat_dt_prop(node, "no-map", NULL) != NULL;
+	default_cma = of_get_flat_dt_prop(node, "linux,cma-default", NULL);
+
+	if (default_cma && cma_skip_dt_default_reserved_mem()) {
+		pr_err("Skipping dt linux,cma-default for \"cma=\" kernel param.\n");
+		return -EINVAL;
+	}
 
 	while (len >= t_len) {
 		base = dt_mem_next_cell(dt_root_addr_cells, &prop);
@@ -256,12 +262,15 @@ void __init fdt_scan_reserved_mem_reg_nodes(void)
 
 	fdt_for_each_subnode(child, fdt, node) {
 		const char *uname;
+		bool default_cma = of_get_flat_dt_prop(child, "linux,cma-default", NULL);
 
 		prop = of_get_flat_dt_prop(child, "reg", &len);
 		if (!prop)
 			continue;
 		if (!of_fdt_device_is_available(fdt, child))
 			continue;
+		if (default_cma && cma_skip_dt_default_reserved_mem())
+			continue;
 
 		uname = fdt_get_name(fdt, child, NULL);
 		if (len && len % t_len != 0) {
@@ -406,7 +415,7 @@ static int __init __reserved_mem_alloc_size(unsigned long node, const char *unam
 	phys_addr_t base = 0, align = 0, size;
 	int len;
 	const __be32 *prop;
-	bool nomap;
+	bool nomap, default_cma;
 	int ret;
 
 	prop = of_get_flat_dt_prop(node, "size", &len);
@@ -430,6 +439,12 @@ static int __init __reserved_mem_alloc_size(unsigned long node, const char *unam
 	}
 
 	nomap = of_get_flat_dt_prop(node, "no-map", NULL) != NULL;
+	default_cma = of_get_flat_dt_prop(node, "linux,cma-default", NULL);
+
+	if (default_cma && cma_skip_dt_default_reserved_mem()) {
+		pr_err("Skipping dt linux,cma-default for \"cma=\" kernel param.\n");
+		return -EINVAL;
+	}
 
 	/* Need adjust the alignment to satisfy the CMA requirement */
 	if (IS_ENABLED(CONFIG_CMA)
diff --git a/include/linux/cma.h b/include/linux/cma.h
index 62d9c1cf6326..3d3047029950 100644
--- a/include/linux/cma.h
+++ b/include/linux/cma.h
@@ -47,6 +47,7 @@ extern int cma_init_reserved_mem(phys_addr_t base, phys_addr_t size,
 					unsigned int order_per_bit,
 					const char *name,
 					struct cma **res_cma);
+extern bool cma_skip_dt_default_reserved_mem(void);
 extern struct page *cma_alloc(struct cma *cma, unsigned long count, unsigned int align,
 			      bool no_warn);
 extern bool cma_pages_valid(struct cma *cma, const struct page *pages, unsigned long count);
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index d9b9dcba6ff7..9071c08650e3 100644
--- a/kernel/dma/contiguous.c
+++ b/kernel/dma/contiguous.c
@@ -90,6 +90,16 @@ static int __init early_cma(char *p)
 }
 early_param("cma", early_cma);
 
+/*
+ * cma_skip_dt_default_reserved_mem - This is called from the
+ * reserved_mem framework to detect if the default cma region is being
+ * set by the "cma=" kernel parameter.
+ */
+bool __init cma_skip_dt_default_reserved_mem(void)
+{
+	return size_cmdline != -1;
+}
+
 #ifdef CONFIG_DMA_NUMA_CMA
 
 static struct cma *dma_contiguous_numa_area[MAX_NUMNODES];
@@ -463,12 +473,6 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
 	struct cma *cma;
 	int err;
 
-	if (size_cmdline != -1 && default_cma) {
-		pr_info("Reserved memory: bypass %s node, using cmdline CMA params instead\n",
-			rmem->name);
-		return -EBUSY;
-	}
-
 	if (!of_get_flat_dt_prop(node, "reusable", NULL) ||
 	    of_get_flat_dt_prop(node, "no-map", NULL))
 		return -EINVAL;
-- 
2.34.1

Re: [PATCH] of: reserved_mem: Allow reserved_mem framework detect "cma=" kernel param

[Rob Herring]

On Tue, Dec 9, 2025 at 6:20 PM Oreoluwa Babatunde
<oreoluwa.babatunde@oss.qualcomm.com> wrote:
>
> When initializing the default cma region, the "cma=" kernel parameter
> takes priority over a DT defined linux,cma-default region. Hence, give
> the reserved_mem framework the ability to detect this so that the DT
> defined cma region can skip initialization accordingly.

Please explain here why this is a new problem. Presumably the
RESERVEDMEM_OF_DECLARE hook after commit xxxx gets called before the
early_param hook. And why is it now earlier?

I don't really like the state/ordering having to be worried about in 2 places.

> Signed-off-by: Oreoluwa Babatunde <oreoluwa.babatunde@oss.qualcomm.com>
> ---
>  drivers/of/of_reserved_mem.c | 19 +++++++++++++++++--
>  include/linux/cma.h          |  1 +
>  kernel/dma/contiguous.c      | 16 ++++++++++------
>  3 files changed, 28 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
> index 2e9ea751ed2d..bef68a4916b5 100644
> --- a/drivers/of/of_reserved_mem.c
> +++ b/drivers/of/of_reserved_mem.c
> @@ -158,7 +158,7 @@ static int __init __reserved_mem_reserve_reg(unsigned long node,
>         phys_addr_t base, size;
>         int len;
>         const __be32 *prop;
> -       bool nomap;
> +       bool nomap, default_cma;
>
>         prop = of_get_flat_dt_prop(node, "reg", &len);
>         if (!prop)
> @@ -171,6 +171,12 @@ static int __init __reserved_mem_reserve_reg(unsigned long node,
>         }
>
>         nomap = of_get_flat_dt_prop(node, "no-map", NULL) != NULL;
> +       default_cma = of_get_flat_dt_prop(node, "linux,cma-default", NULL);
> +
> +       if (default_cma && cma_skip_dt_default_reserved_mem()) {
> +               pr_err("Skipping dt linux,cma-default for \"cma=\" kernel param.\n");
> +               return -EINVAL;
> +       }
>
>         while (len >= t_len) {
>                 base = dt_mem_next_cell(dt_root_addr_cells, &prop);
> @@ -256,12 +262,15 @@ void __init fdt_scan_reserved_mem_reg_nodes(void)
>
>         fdt_for_each_subnode(child, fdt, node) {
>                 const char *uname;
> +               bool default_cma = of_get_flat_dt_prop(child, "linux,cma-default", NULL);
>
>                 prop = of_get_flat_dt_prop(child, "reg", &len);
>                 if (!prop)
>                         continue;
>                 if (!of_fdt_device_is_available(fdt, child))
>                         continue;
> +               if (default_cma && cma_skip_dt_default_reserved_mem())
> +                       continue;
>
>                 uname = fdt_get_name(fdt, child, NULL);
>                 if (len && len % t_len != 0) {
> @@ -406,7 +415,7 @@ static int __init __reserved_mem_alloc_size(unsigned long node, const char *unam
>         phys_addr_t base = 0, align = 0, size;
>         int len;
>         const __be32 *prop;
> -       bool nomap;
> +       bool nomap, default_cma;
>         int ret;
>
>         prop = of_get_flat_dt_prop(node, "size", &len);
> @@ -430,6 +439,12 @@ static int __init __reserved_mem_alloc_size(unsigned long node, const char *unam
>         }
>
>         nomap = of_get_flat_dt_prop(node, "no-map", NULL) != NULL;
> +       default_cma = of_get_flat_dt_prop(node, "linux,cma-default", NULL);
> +
> +       if (default_cma && cma_skip_dt_default_reserved_mem()) {
> +               pr_err("Skipping dt linux,cma-default for \"cma=\" kernel param.\n");
> +               return -EINVAL;
> +       }
>
>         /* Need adjust the alignment to satisfy the CMA requirement */
>         if (IS_ENABLED(CONFIG_CMA)
> diff --git a/include/linux/cma.h b/include/linux/cma.h
> index 62d9c1cf6326..3d3047029950 100644
> --- a/include/linux/cma.h
> +++ b/include/linux/cma.h
> @@ -47,6 +47,7 @@ extern int cma_init_reserved_mem(phys_addr_t base, phys_addr_t size,
>                                         unsigned int order_per_bit,
>                                         const char *name,
>                                         struct cma **res_cma);
> +extern bool cma_skip_dt_default_reserved_mem(void);
>  extern struct page *cma_alloc(struct cma *cma, unsigned long count, unsigned int align,
>                               bool no_warn);
>  extern bool cma_pages_valid(struct cma *cma, const struct page *pages, unsigned long count);
> diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
> index d9b9dcba6ff7..9071c08650e3 100644
> --- a/kernel/dma/contiguous.c
> +++ b/kernel/dma/contiguous.c
> @@ -90,6 +90,16 @@ static int __init early_cma(char *p)
>  }
>  early_param("cma", early_cma);
>
> +/*
> + * cma_skip_dt_default_reserved_mem - This is called from the
> + * reserved_mem framework to detect if the default cma region is being
> + * set by the "cma=" kernel parameter.
> + */
> +bool __init cma_skip_dt_default_reserved_mem(void)
> +{
> +       return size_cmdline != -1;
> +}
> +
>  #ifdef CONFIG_DMA_NUMA_CMA
>
>  static struct cma *dma_contiguous_numa_area[MAX_NUMNODES];
> @@ -463,12 +473,6 @@ static int __init rmem_cma_setup(struct reserved_mem *rmem)
>         struct cma *cma;
>         int err;
>
> -       if (size_cmdline != -1 && default_cma) {
> -               pr_info("Reserved memory: bypass %s node, using cmdline CMA params instead\n",
> -                       rmem->name);
> -               return -EBUSY;
> -       }
> -
>         if (!of_get_flat_dt_prop(node, "reusable", NULL) ||
>             of_get_flat_dt_prop(node, "no-map", NULL))
>                 return -EINVAL;
> --
> 2.34.1
>
>

Re: [PATCH] of: reserved_mem: Allow reserved_mem framework detect "cma=" kernel param

[kernel test robot]

Hi Oreoluwa,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]
[also build test ERROR on v6.18]
[cannot apply to robh/for-next linus/master next-20251212]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Oreoluwa-Babatunde/of-reserved_mem-Allow-reserved_mem-framework-detect-cma-kernel-param/20251210-082127
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20251210002027.1171519-1-oreoluwa.babatunde%40oss.qualcomm.com
patch subject: [PATCH] of: reserved_mem: Allow reserved_mem framework detect "cma=" kernel param
config: arc-randconfig-001-20251212 (https://download.01.org/0day-ci/archive/20251212/202512121907.gdTOodx3-lkp@intel.com/config)
compiler: arc-linux-gcc (GCC) 8.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251212/202512121907.gdTOodx3-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512121907.gdTOodx3-lkp@intel.com/

All errors (new ones prefixed by >>):

   arc-linux-ld: drivers/of/of_reserved_mem.o: in function `fdt_scan_reserved_mem_reg_nodes':
>> of_reserved_mem.c:(.init.text+0x46e): undefined reference to `cma_skip_dt_default_reserved_mem'
>> arc-linux-ld: of_reserved_mem.c:(.init.text+0x46e): undefined reference to `cma_skip_dt_default_reserved_mem'
   arc-linux-ld: drivers/of/of_reserved_mem.o: in function `fdt_scan_reserved_mem':
   of_reserved_mem.c:(.init.text+0x618): undefined reference to `cma_skip_dt_default_reserved_mem'
   arc-linux-ld: of_reserved_mem.c:(.init.text+0x618): undefined reference to `cma_skip_dt_default_reserved_mem'
   arc-linux-ld: of_reserved_mem.c:(.init.text+0x77c): undefined reference to `cma_skip_dt_default_reserved_mem'
   arc-linux-ld: drivers/of/of_reserved_mem.o:of_reserved_mem.c:(.init.text+0x77c): more undefined references to `cma_skip_dt_default_reserved_mem' follow

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki

Re: [PATCH] of: reserved_mem: Allow reserved_mem framework detect "cma=" kernel param

[kernel test robot]

Hi Oreoluwa,

kernel test robot noticed the following build errors:

[auto build test ERROR on akpm-mm/mm-everything]
[also build test ERROR on v6.18]
[cannot apply to robh/for-next linus/master next-20251212]
[If your patch is applied to the wrong git tree, kindly drop us a note.
And when submitting patch, we suggest to use '--base' as documented in
https://git-scm.com/docs/git-format-patch#_base_tree_information]

url:    https://github.com/intel-lab-lkp/linux/commits/Oreoluwa-Babatunde/of-reserved_mem-Allow-reserved_mem-framework-detect-cma-kernel-param/20251210-082127
base:   https://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm.git mm-everything
patch link:    https://lore.kernel.org/r/20251210002027.1171519-1-oreoluwa.babatunde%40oss.qualcomm.com
patch subject: [PATCH] of: reserved_mem: Allow reserved_mem framework detect "cma=" kernel param
config: nios2-randconfig-r073-20251212 (https://download.01.org/0day-ci/archive/20251212/202512121807.G5FMUgvU-lkp@intel.com/config)
compiler: nios2-linux-gcc (GCC) 10.5.0
reproduce (this is a W=1 build): (https://download.01.org/0day-ci/archive/20251212/202512121807.G5FMUgvU-lkp@intel.com/reproduce)

If you fix the issue in a separate patch/commit (i.e. not just a new version of
the same patch/commit), kindly add following tags
| Reported-by: kernel test robot <lkp@intel.com>
| Closes: https://lore.kernel.org/oe-kbuild-all/202512121807.G5FMUgvU-lkp@intel.com/

All errors (new ones prefixed by >>):

   nios2-linux-ld: drivers/of/of_reserved_mem.o: in function `__reserved_mem_reserve_reg':
>> drivers/of/of_reserved_mem.c:176: undefined reference to `cma_skip_dt_default_reserved_mem'
>> drivers/of/of_reserved_mem.c:176:(.init.text+0x5b8): relocation truncated to fit: R_NIOS2_CALL26 against `cma_skip_dt_default_reserved_mem'
   nios2-linux-ld: drivers/of/of_reserved_mem.o: in function `__reserved_mem_alloc_size':
   drivers/of/of_reserved_mem.c:444: undefined reference to `cma_skip_dt_default_reserved_mem'
   drivers/of/of_reserved_mem.c:444:(.init.text+0x8a4): relocation truncated to fit: R_NIOS2_CALL26 against `cma_skip_dt_default_reserved_mem'
   nios2-linux-ld: drivers/of/of_reserved_mem.o: in function `fdt_scan_reserved_mem_reg_nodes':
   drivers/of/of_reserved_mem.c:272: undefined reference to `cma_skip_dt_default_reserved_mem'
   drivers/of/of_reserved_mem.c:272:(.init.text+0xbb0): relocation truncated to fit: R_NIOS2_CALL26 against `cma_skip_dt_default_reserved_mem'


vim +176 drivers/of/of_reserved_mem.c

   150	
   151	/*
   152	 * __reserved_mem_reserve_reg() - reserve all memory described in 'reg' property
   153	 */
   154	static int __init __reserved_mem_reserve_reg(unsigned long node,
   155						     const char *uname)
   156	{
   157		int t_len = (dt_root_addr_cells + dt_root_size_cells) * sizeof(__be32);
   158		phys_addr_t base, size;
   159		int len;
   160		const __be32 *prop;
   161		bool nomap, default_cma;
   162	
   163		prop = of_get_flat_dt_prop(node, "reg", &len);
   164		if (!prop)
   165			return -ENOENT;
   166	
   167		if (len && len % t_len != 0) {
   168			pr_err("Reserved memory: invalid reg property in '%s', skipping node.\n",
   169			       uname);
   170			return -EINVAL;
   171		}
   172	
   173		nomap = of_get_flat_dt_prop(node, "no-map", NULL) != NULL;
   174		default_cma = of_get_flat_dt_prop(node, "linux,cma-default", NULL);
   175	
 > 176		if (default_cma && cma_skip_dt_default_reserved_mem()) {
   177			pr_err("Skipping dt linux,cma-default for \"cma=\" kernel param.\n");
   178			return -EINVAL;
   179		}
   180	
   181		while (len >= t_len) {
   182			base = dt_mem_next_cell(dt_root_addr_cells, &prop);
   183			size = dt_mem_next_cell(dt_root_size_cells, &prop);
   184	
   185			if (size && early_init_dt_reserve_memory(base, size, nomap) == 0) {
   186				/* Architecture specific contiguous memory fixup. */
   187				if (of_flat_dt_is_compatible(node, "shared-dma-pool") &&
   188				    of_get_flat_dt_prop(node, "reusable", NULL))
   189					dma_contiguous_early_fixup(base, size);
   190				pr_debug("Reserved memory: reserved region for node '%s': base %pa, size %lu MiB\n",
   191					uname, &base, (unsigned long)(size / SZ_1M));
   192			} else {
   193				pr_err("Reserved memory: failed to reserve memory for node '%s': base %pa, size %lu MiB\n",
   194				       uname, &base, (unsigned long)(size / SZ_1M));
   195			}
   196	
   197			len -= t_len;
   198		}
   199		return 0;
   200	}
   201	

-- 
0-DAY CI Kernel Test Service
https://github.com/intel/lkp-tests/wiki