[PATCH 6.18 049/122] of: reserved_mem: Allow reserved_mem framework detect "cma=" kernel param

Greg Kroah-Hartman
2026-02-04T15:30:40Z

From: Oreoluwa Babatunde <oreoluwa.babatunde@oss.qualcomm.com>

[ Upstream commit 0fd17e5983337231dc655e9ca0095d2ca3f47405 ]

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>
Tested-by: Joy Zou <joy.zou@nxp.com>
Acked-by: Rob Herring (Arm) <robh@kernel.org>
Fixes: 8a6e02d0c00e ("of: reserved_mem: Restructure how the reserved memory regions are processed")
Fixes: 2c223f7239f3 ("of: reserved_mem: Restructure call site for dma_contiguous_early_fixup()")
Link: https://lore.kernel.org/r/20251210002027.1171519-1-oreoluwa.babatunde@oss.qualcomm.com
[mszyprow: rebased onto v6.19-rc1, added fixes tags, added a stub for
cma_skip_dt_default_reserved_mem() if no CONFIG_DMA_CMA is set]
Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
drivers/of/of_reserved_mem.c | 19 +++++++++++++++++--
include/linux/cma.h | 9 +++++++++
kernel/dma/contiguous.c | 16 ++++++++++------
3 files changed, 36 insertions(+), 8 deletions(-)

diff --git a/drivers/of/of_reserved_mem.c b/drivers/of/of_reserved_mem.c
index e5ea4f1e5eff7..fe111d1ea7397 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);
@@ -253,10 +259,13 @@ 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);
u64 b, s;

if (!of_fdt_device_is_available(fdt, child))
continue;
+ if (default_cma && cma_skip_dt_default_reserved_mem())
+ continue;

if (!of_flat_dt_get_addr_size(child, "reg", &b, &s))
continue;
@@ -395,7 +404,7 @@ 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);
@@ -419,6 +428,12 @@ 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 62d9c1cf63265..2e6931735880b 100644
--- a/include/linux/cma.h
+++ b/include/linux/cma.h
@@ -57,6 +57,15 @@ extern bool cma_intersects(struct cma *cma, unsigned long start, unsigned long e

extern void cma_reserve_pages_on_error(struct cma *cma);

+#ifdef CONFIG_DMA_CMA
+extern bool cma_skip_dt_default_reserved_mem(void);
+#else
+static inline bool cma_skip_dt_default_reserved_mem(void)
+{
+ return false;
+}
+#endif
+
#ifdef CONFIG_CMA
struct folio *cma_alloc_folio(struct cma *cma, int order, gfp_t gfp);
bool cma_free_folio(struct cma *cma, const struct folio *folio);
diff --git a/kernel/dma/contiguous.c b/kernel/dma/contiguous.c
index d9b9dcba6ff7c..9071c08650e3a 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;
--
2.51.0