linux-kernel - [RFC PATCH 3/3] m68k: Add dt support (proof of concept)

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Message-ID: <20250105071433.3943289-4-daniel@0x0f.com>
Date: Sun,  5 Jan 2025 16:14:33 +0900
From: Daniel Palmer <daniel@...f.com>
To: geert@...ux-m68k.org,
	fthain@...ux-m68k.org,
	linux-m68k@...ts.linux-m68k.org
Cc: linux-kernel@...r.kernel.org,
	Daniel Palmer <daniel@...f.com>
Subject: [RFC PATCH 3/3] m68k: Add dt support (proof of concept)

This is not ready for merge. This just adds enough, probably incorrect,
code to get the FDT blob from the bootinfo and parse it.

This is enough to get drivers to probe using devicetree nodes instead
of manually registering them but looking up interrupts etc in the DT
will not work.

Signed-off-by: Daniel Palmer <daniel@...f.com>
---
 arch/m68k/Kconfig           |  2 ++
 arch/m68k/kernel/setup_mm.c | 63 ++++++++++++++++++++++++++++++++++++-
 2 files changed, 64 insertions(+), 1 deletion(-)

diff --git a/arch/m68k/Kconfig b/arch/m68k/Kconfig
index 7c4f7bcc89d7..e348e6822943 100644
--- a/arch/m68k/Kconfig
+++ b/arch/m68k/Kconfig
@@ -39,6 +39,8 @@ config M68K
 	select OLD_SIGSUSPEND3
 	select UACCESS_MEMCPY if !MMU
 	select ZONE_DMA
+	select OF
+	select OF_EARLY_FLATTREE
 
 config CPU_BIG_ENDIAN
 	def_bool y
diff --git a/arch/m68k/kernel/setup_mm.c b/arch/m68k/kernel/setup_mm.c
index 15c1a595a1de..6d358124259e 100644
--- a/arch/m68k/kernel/setup_mm.c
+++ b/arch/m68k/kernel/setup_mm.c
@@ -50,6 +50,10 @@
 #include <asm/natfeat.h>
 #include <asm/config.h>
 
+#include <linux/libfdt.h>
+#include <linux/of.h>
+#include <linux/of_fdt.h>
+
 #if !FPSTATESIZE || !NR_IRQS
 #warning No CPU/platform type selected, your kernel will not work!
 #warning Are you building an allnoconfig kernel?
@@ -107,11 +111,57 @@ EXPORT_SYMBOL(isa_sex);
 
 #define MASK_256K 0xfffc0000
 
+static phys_addr_t fdt_blob;
+static void __init m68k_setup_fdt(void)
+{
+	pr_info("m68k generic DT machine support, FDT blob at 0x%08x\n", fdt_blob);
+	if (!early_init_dt_verify(__va(fdt_blob), fdt_blob)) {
+		pr_err("FDT blob is bad?!\n");
+		return;
+	}
+
+	early_init_dt_scan_nodes();
+}
+
+static const struct bi_record __init *m68k_find_bootinfo_record(const struct bi_record *record, u16 bi_type)
+{
+	uint16_t tag;
+
+	while ((tag = be16_to_cpu(record->tag)) != BI_LAST) {
+		uint16_t size = be16_to_cpu(record->size);
+
+		if (tag == bi_type)
+			return record;
+		record = (struct bi_record *)((unsigned long)record + size);
+	}
+
+	return NULL;
+}
+
 static void __init m68k_parse_bootinfo(const struct bi_record *record)
 {
 	const struct bi_record *first_record = record;
+	const struct bi_record *machine_record;
 	uint16_t tag;
 
+	fdt_blob = 0;
+
+	/*
+	 * First attempt to work out if we are a generic DT machine,
+	 * must have an FDT record.
+	 */
+	machine_record = m68k_find_bootinfo_record(record, BI_MACHTYPE);
+	if (machine_record->data[0] == MACH_GENERIC) {
+		const struct bi_record *fdt_record;
+
+		fdt_record = m68k_find_bootinfo_record(record, BI_FDT);
+
+		BUG_ON(!fdt_record);
+		fdt_blob = (phys_addr_t) fdt_record->data[0];
+	}
+
+	/* Revert to the pure bootinfo method */
+	record = first_record;
 	while ((tag = be16_to_cpu(record->tag)) != BI_LAST) {
 		int unknown = 0;
 		const void *data = record->data;
@@ -124,7 +174,6 @@ static void __init m68k_parse_bootinfo(const struct bi_record *record)
 		case BI_MMUTYPE:
 			/* Already set up by head.S */
 			break;
-
 		case BI_MEMCHUNK:
 			if (m68k_num_memory < NUM_MEMINFO) {
 				const struct mem_info *m = data;
@@ -162,6 +211,10 @@ static void __init m68k_parse_bootinfo(const struct bi_record *record)
 			break;
 		}
 
+		case BI_FDT:
+			fdt_blob = (phys_addr_t) record->data[0];
+			break;
+
 		default:
 			if (MACH_IS_AMIGA)
 				unknown = amiga_parse_bootinfo(record);
@@ -240,6 +293,9 @@ void __init setup_arch(char **cmdline_p)
 		}
 	}
 
+	if (fdt_blob)
+		m68k_setup_fdt();
+
 	setup_initial_init_mm((void *)PAGE_OFFSET, _etext, _edata, _end);
 
 #if defined(CONFIG_BOOTPARAM)
@@ -329,6 +385,11 @@ void __init setup_arch(char **cmdline_p)
 		panic("No configuration setup");
 	}
 
+	if (fdt_blob) {
+		memblock_reserve(fdt_blob, fdt_totalsize(__va(fdt_blob)));
+		unflatten_device_tree();
+	}
+
 	if (IS_ENABLED(CONFIG_BLK_DEV_INITRD) && m68k_ramdisk.size)
 		memblock_reserve(m68k_ramdisk.addr, m68k_ramdisk.size);
 
-- 
2.45.2