[PATCH] spl: Add generic SPL MTD loader support

[Fabio Estevam <festevam@gmail.com>]

From: Fabio Estevam <festevam@nabladev.com>

Add support for loading the next stage from an MTD device in SPL.

Introduce CONFIG_SPL_MTD_LOAD and a generic SPL MTD loader
implementation that uses the MTD subsystem to read the U-Boot payload.

The loader works with any MTD-backed storage, including raw NAND and
SPI NAND, without being tied to a specific NAND type.

The payload offset defaults to CONFIG_SYS_MTD_U_BOOT_OFFS and can be
overridden via the device tree property:

    u-boot,spl-payload-offset

To support both raw NAND and SPI NAND boot flows, the loader is
registered for BOOT_DEVICE_NAND and BOOT_DEVICE_SPI. This allows it
to operate correctly on platforms where the ROM reports either NAND
or SPI as the boot source while using the same MTD-based loading
infrastructure.

The required NAND core and SPI NAND drivers are built for SPL when
CONFIG_SPL_MTD_LOAD is enabled.

This provides reusable infrastructure for boards that boot from MTD
devices without relying on SPI-specific or NAND-specific SPL loaders.

Signed-off-by: Fabio Estevam <festevam@nabladev.com>
---
Dinesh,

Could you please test this approach on your boards?

Thanks

 common/spl/Kconfig        | 15 +++++++
 common/spl/Makefile       |  1 +
 common/spl/spl_mtd.c      | 88 +++++++++++++++++++++++++++++++++++++++
 drivers/mtd/Makefile      |  1 +
 drivers/mtd/nand/Makefile | 12 +++++-
 5 files changed, 116 insertions(+), 1 deletion(-)
 create mode 100644 common/spl/spl_mtd.c

diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index 2998b7acb75f..2aba6da73c10 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -1576,8 +1576,23 @@ config SPL_SPI_LOAD
 	  Enable support for loading next stage, U-Boot or otherwise, from
 	  SPI NOR in U-Boot SPL.
 
+config SPL_MTD_LOAD
+	bool "Support loading from a generic MTD device"
+	depends on SPL
+	depends on MTD && DM_MTD
+	help
+	  Enable support for loading next stage, U-Boot or otherwise, from
+	  a generic MTD device (raw NAND, SPI NAND) in U-Boot SPL.
+
 endif # SPL_SPI_FLASH_SUPPORT
 
+config SYS_MTD_U_BOOT_OFFS
+	hex "address of u-boot payload in the MTD device"
+	default 0x0
+	help
+	 Address within the MTD device where the u-boot payload is fetched
+	 from.
+
 config SYS_SPI_U_BOOT_OFFS
 	hex "address of u-boot payload in SPI flash"
 	default 0x8000 if ARCH_SUNXI
diff --git a/common/spl/Makefile b/common/spl/Makefile
index 4c9482bd3096..9f5ddcad17af 100644
--- a/common/spl/Makefile
+++ b/common/spl/Makefile
@@ -35,6 +35,7 @@ obj-$(CONFIG_$(PHASE_)NVME) += spl_nvme.o
 obj-$(CONFIG_$(PHASE_)SEMIHOSTING) += spl_semihosting.o
 obj-$(CONFIG_$(PHASE_)DFU) += spl_dfu.o
 obj-$(CONFIG_$(PHASE_)SPI_LOAD) += spl_spi.o
+obj-$(CONFIG_$(PHASE_)MTD_LOAD) += spl_mtd.o
 obj-$(CONFIG_$(PHASE_)RAM_SUPPORT) += spl_ram.o
 obj-$(CONFIG_$(PHASE_)USB_SDP_SUPPORT) += spl_sdp.o
 endif
diff --git a/common/spl/spl_mtd.c b/common/spl/spl_mtd.c
new file mode 100644
index 000000000000..8c6c94e592d0
--- /dev/null
+++ b/common/spl/spl_mtd.c
@@ -0,0 +1,88 @@
+// SPDX-License-Identifier: GPL-2.0+
+
+/*
+ * Generic SPL loader for MTD devices.
+ *
+ * Based on spl_spi.c, which is:
+ *
+ * Copyright (C) 2011 OMICRON electronics GmbH
+ *
+ * based on drivers/mtd/nand/raw/nand_spl_load.c
+ *
+ * Copyright (C) 2011
+ * Heiko Schocher, DENX Software Engineering, hs@denx.de.
+ */
+
+#include <config.h>
+#include <errno.h>
+#include <image.h>
+#include <log.h>
+#include <spl.h>
+#include <spl_load.h>
+
+#include <dm.h>
+#include <dm/ofnode.h>
+#include <dm/uclass.h>
+#include <mtd.h>
+
+static struct mtd_info *spl_mtd_get_device(void)
+{
+	struct udevice *dev;
+	int ret;
+
+	for (ret = uclass_first_device_err(UCLASS_MTD, &dev);
+	     dev;
+	     ret = uclass_next_device_err(&dev)) {
+		if (ret)
+			continue;
+
+		return dev_get_uclass_priv(dev);
+	}
+
+	return NULL;
+}
+
+static ulong spl_mtd_read(struct spl_load_info *load,
+			  ulong offs, ulong size, void *buf)
+{
+	struct mtd_info *mtd = load->priv;
+	size_t retlen;
+	int ret;
+
+	ret = mtd_read(mtd, offs, size, &retlen, buf);
+	if (ret && !mtd_is_bitflip(ret))
+		return 0;
+
+	if (retlen != size)
+		return 0;
+
+	return retlen;
+}
+
+static int spl_mtd_load_image(struct spl_image_info *spl_image,
+			      struct spl_boot_device *bootdev)
+{
+	struct spl_load_info load;
+	struct mtd_info *mtd;
+	ulong offset;
+
+	mtd = spl_mtd_get_device();
+	if (!mtd) {
+		debug("No MTD device found\n");
+		return -ENODEV;
+	}
+
+	spl_load_init(&load, spl_mtd_read, mtd, mtd->writesize);
+
+	offset = CONFIG_SYS_MTD_U_BOOT_OFFS;
+
+	if (CONFIG_IS_ENABLED(OF_REAL))
+		offset = ofnode_conf_read_int("u-boot,spl-payload-offset",
+					      offset);
+
+	return spl_load(spl_image, bootdev, &load, 0, offset);
+}
+
+/* Priority 1 so boards may override */
+SPL_LOAD_IMAGE_METHOD("MTD-NAND", 1, BOOT_DEVICE_NAND, spl_mtd_load_image);
+SPL_LOAD_IMAGE_METHOD("MTD-SPI-NAND", 1, BOOT_DEVICE_SPI, spl_mtd_load_image);
diff --git a/drivers/mtd/Makefile b/drivers/mtd/Makefile
index ce05e206073d..0856a8f68732 100644
--- a/drivers/mtd/Makefile
+++ b/drivers/mtd/Makefile
@@ -34,6 +34,7 @@ else
 ifneq ($(mtd-y),)
 obj-$(CONFIG_SPL_MTD) += mtd.o
 endif
+obj-$(CONFIG_SPL_MTD_LOAD) += nand/
 obj-$(CONFIG_$(PHASE_)NAND_SUPPORT) += nand/
 obj-$(CONFIG_SPL_ONENAND_SUPPORT) += onenand/
 obj-$(CONFIG_$(PHASE_)SPI_FLASH_SUPPORT) += spi/
diff --git a/drivers/mtd/nand/Makefile b/drivers/mtd/nand/Makefile
index c8169cf73902..cd6eaa87739c 100644
--- a/drivers/mtd/nand/Makefile
+++ b/drivers/mtd/nand/Makefile
@@ -1,10 +1,20 @@
 # SPDX-License-Identifier: GPL-2.0+
 
-ifeq ($(CONFIG_XPL_BUILD)$(CONFIG_TPL_BUILD),)
 nandcore-objs := core.o bbt.o
+
+ifeq ($(CONFIG_XPL_BUILD),)
+
+# U-Boot proper
 obj-$(CONFIG_MTD_NAND_CORE) += nandcore.o
 obj-$(CONFIG_MTD_RAW_NAND) += raw/
 obj-$(CONFIG_MTD_SPI_NAND) += spi/
+
 else
+
+# XPL
+obj-$(CONFIG_SPL_MTD_LOAD) += nandcore.o
+obj-$(CONFIG_SPL_MTD_LOAD) += spi/
+
+# raw NAND still follows the normal SPL rule
 obj-$(CONFIG_$(PHASE_)NAND_SUPPORT) += raw/
 endif
-- 
2.34.1