[RFC PATCH 2/3] riscv: Add early_param to decrease firmware region

[guoren@kernel.org]

From: Guo Ren <guoren@linux.alibaba.com>

Using riscv.fw_size in cmdline to tell the kernel what the
firmware (opensbi) size is. Then reserve the proper size of
firmware to save memory instead of the whole 2MB. It's helpful
to satisfy a small memory system (D1s/F133 from Allwinner).

Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: Anup Patel <anup.patel@wdc.com>
Cc: Atish Patra <atishp@rivosinc.com>
---
 arch/riscv/mm/init.c | 14 +++++++++++++-
 1 file changed, 13 insertions(+), 1 deletion(-)

diff --git a/arch/riscv/mm/init.c b/arch/riscv/mm/init.c
index 920e78f8c3e4..f7db6d40213d 100644
--- a/arch/riscv/mm/init.c
+++ b/arch/riscv/mm/init.c
@@ -159,6 +159,15 @@ static int __init early_mem(char *p)
 }
 early_param("mem", early_mem);
 
+static phys_addr_t firmware_size __initdata;
+static int __init early_get_firmware_size(char *arg)
+{
+	firmware_size = memparse(arg, &arg);
+
+	return 0;
+}
+early_param("riscv.fwsz", early_get_firmware_size);
+
 static void __init setup_bootmem(void)
 {
 	phys_addr_t vmlinux_end = __pa_symbol(&_end);
@@ -224,7 +233,10 @@ static void __init setup_bootmem(void)
 	/*
 	 * Reserve OpenSBI region and depends on PMP to deny accesses.
 	 */
-	memblock_reserve(__pa(PAGE_OFFSET), LOAD_OFFSET);
+	if (firmware_size > PAGE_SIZE)
+		memblock_reserve(__pa(PAGE_OFFSET), firmware_size);
+	else
+		memblock_reserve(__pa(PAGE_OFFSET), LOAD_OFFSET);
 
 	early_init_fdt_scan_reserved_mem();
 	dma_contiguous_reserve(dma32_phys_limit);
-- 
2.25.1