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Message-ID: <CAL_JsqL6VVQ7K_ZAbHJ8Gb7ei_jusLx6wRn=AdOVgV50dX0ejQ@mail.gmail.com>
Date: Wed, 10 Dec 2025 08:07:40 -0600
From: Rob Herring <robh@...nel.org>
To: Oreoluwa Babatunde <oreoluwa.babatunde@....qualcomm.com>
Cc: m.szyprowski@...sung.com, ye.li@....nxp.com, kernel@....qualcomm.com,
saravanak@...gle.com, akpm@...ux-foundation.org, david@...hat.com,
lorenzo.stoakes@...cle.com, Liam.Howlett@...cle.com, vbabka@...e.cz,
rppt@...nel.org, surenb@...gle.com, mhocko@...e.com, robin.murphy@....com,
devicetree@...r.kernel.org, linux-kernel@...r.kernel.org, linux-mm@...ck.org,
iommu@...ts.linux.dev, quic_c_gdjako@...cinc.com
Subject: Re: [PATCH] of: reserved_mem: Allow reserved_mem framework detect
"cma=" kernel param
On Tue, Dec 9, 2025 at 6:20 PM Oreoluwa Babatunde
<oreoluwa.babatunde@....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@....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
>
>
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