Re: [PATCHv2 1/5] lmb: add LMB_FDT for fdt reserved regions

Heinrich Schuchardt
2026-04-09T19:15:34Z

Am 2. April 2026 22:50:34 MESZ schrieb rs@ti.com:
>From: Randolph Sapp <rs@ti.com>
>
>Add an LMB_FDT bit for fdt reserved regions, so we can reclaim them when
>parsing a new device tree and properly warn people when a reservation
>overlaps with an existing allocation.
>
>If we don't at least warn the user of these reservation failures,
>there's a chance that this region could be freed and reallocated for
>something important later.
>
>This useful warning mechanism was broken in:
>5a6aa7d5913 ("boot: fdt: Handle already reserved memory in boot_fdt_reserve_region()")
>
>Signed-off-by: Randolph Sapp <rs@ti.com>
>---
> boot/image-fdt.c | 5 ++++-
> include/lmb.h | 7 +++++++
> lib/lmb.c | 25 +++++++++++++++++++++++++
> 3 files changed, 36 insertions(+), 1 deletion(-)
>
>diff --git a/boot/image-fdt.c b/boot/image-fdt.c
>index a3a4fb8b558..0f5857f24d2 100644
>--- a/boot/image-fdt.c
>+++ b/boot/image-fdt.c
>@@ -73,6 +73,7 @@ static void boot_fdt_reserve_region(u64 addr, u64 size, u32 flags)
> {
> long ret;
> phys_addr_t rsv_addr;
>+ flags |= LMB_FDT;
>
> rsv_addr = (phys_addr_t)addr;
> ret = lmb_alloc_mem(LMB_MEM_ALLOC_ADDR, 0, &rsv_addr, size, flags);
>@@ -80,7 +81,7 @@ static void boot_fdt_reserve_region(u64 addr, u64 size, u32 flags)
> debug(" reserving fdt memory region: addr=%llx size=%llx flags=%x\n",
> (unsigned long long)addr,
> (unsigned long long)size, flags);
>- } else if (ret != -EEXIST && ret != -EINVAL) {
>+ } else if (ret != -EINVAL) {
> puts("ERROR: reserving fdt memory region failed ");
> printf("(addr=%llx size=%llx flags=%x)\n",
> (unsigned long long)addr,
>@@ -108,6 +109,8 @@ void boot_fdt_add_mem_rsv_regions(void *fdt_blob)
> if (fdt_check_header(fdt_blob) != 0)
> return;
>
>+ lmb_free_fdt_regions();
>+
> /* process memreserve sections */
> total = fdt_num_mem_rsv(fdt_blob);
> for (i = 0; i < total; i++) {
>diff --git a/include/lmb.h b/include/lmb.h
>index 5d5f037ccb9..1b59a63f61d 100644
>--- a/include/lmb.h
>+++ b/include/lmb.h
>@@ -25,11 +25,13 @@
> * %LMB_NOMAP: Don't add to MMU configuration
> * %LMB_NOOVERWRITE: The memory region cannot be overwritten/re-reserved
> * %LMB_NONOTIFY: Do not notify other modules of changes to this memory region
>+ * %LMB_FDT: A FDT reserved region that can be reclaimed if the FDT changes
> */
> #define LMB_NONE 0
> #define LMB_NOMAP BIT(1)
> #define LMB_NOOVERWRITE BIT(2)
> #define LMB_NONOTIFY BIT(3)
>+#define LMB_FDT BIT(4)

Please, document the constants according to https://docs.kernel.org/doc-guide/kernel-doc.html#object-like-macro-documentation . This allows Sphinx to generate the API documentation.

Best regards

Heinrich

>
> /**
> * enum lmb_mem_type - type of memory allocation request
>@@ -215,6 +217,11 @@ phys_addr_t io_lmb_alloc(struct lmb *io_lmb, phys_size_t size, ulong align);
> */
> long io_lmb_free(struct lmb *io_lmb, phys_addr_t base, phys_size_t size);
>
>+/**
>+ * lmb_free_fdt_regions() - Reclaim all LMB_FDT tagged reserved regions
>+ */
>+void lmb_free_fdt_regions(void);
>+
> #endif /* __KERNEL__ */
>
> #endif /* _LINUX_LMB_H */
>diff --git a/lib/lmb.c b/lib/lmb.c
>index e2d9fe86c14..18703212afb 100644
>--- a/lib/lmb.c
>+++ b/lib/lmb.c
>@@ -669,6 +669,31 @@ long lmb_free(phys_addr_t base, phys_size_t size, u32 flags)
> return lmb_map_update_notify(base, size, LMB_MAP_OP_FREE, flags);
> }
>
>+void lmb_free_fdt_regions(void)
>+{
>+ struct alist *lmb_rgn_lst = &lmb.used_mem;
>+ struct lmb_region *rgn = lmb_rgn_lst->data;
>+ long ret;
>+ int i = 0;
>+
>+ while (i < lmb_rgn_lst->count) {
>+ phys_addr_t base = rgn[i].base;
>+ phys_size_t size = rgn[i].size;
>+ u32 flags = rgn[i].flags;
>+
>+ if (flags & LMB_FDT) {
>+ ret = lmb_free(base, size, flags);
>+ if (ret < 0) {
>+ printf("Unable to free FDT memory at 0x%08lx",
>+ (ulong)base);
>+ i++;
>+ }
>+ } else {
>+ i++;
>+ }
>+ }
>+}
>+
> static int _lmb_alloc_base(phys_size_t size, ulong align,
> phys_addr_t *addr, u32 flags)
> {