Re: Trying to get MTD_BLOCK to actually work

On 17-08-2026 17:55, Heinrich Schuchardt wrote:
> On 8/17/26 17:00, Mike Looijmans wrote:
>> What I'm trying to accomplish is to be able to read the kernel 
>> directly from a squashfs partition in SPI NOR flash.
>>
>> This should have been simple, as SPI-NOR is an MTD device, and 
>> MTD_BLOCK translates that to a block device, and squashfs needs a 
>> block device.
>>
>> The issue is that MTD_BLOCK adds some hooks, in particular 
>> "mtd_bind()" but the only point where that ever gets called is from 
>> drivers/mtd/nand/ spi/core.c
>>
>> So even though one activates CONFIG_MTD_BLOCK, no mtd device or 
>> partition ever gets registered as a block device (unless you happen 
>> to have a spi-nand controller, which, contrary to spi-nor, would be 
>> unsuitable for a squashfs filesystem...)
>>
>> I tried doing the obvious, that is, copy and adapt the spi-nand code 
>> into the spi-nor driver, see attached patch, but that doesn't have 
>> any effect whatsoever.
>>
>> I tried similar things a few months ago, and also had a discussion 
>> here on the list, but that sort of faded out without any further 
>> results...
>
>
> spi_flash_std_bind() is called before spi_flash_std_probe(). Setting 
> plat->mtd in spi_flash_std_probe() will have no effect in the bind 
> method.

Tried putting something together in an updated patch. Seems to have some 
effect now. Some block device registers now, but there's no working link 
to the partitioning:



zynq-uboot> lsblk
Block Driver          Devices
-----------------------------
mmc_blk             : mmc 0
mtd_blk             : mtd 0
ubi_blk             : mtd 1
usb_storage_blk     : <none>
zynq-uboot> dm tree
  Class     Seq    Probed  Driver                Name
-----------------------------------------------------------
  root          0  [ + ]   root_driver           root_driver
  simple_bus    0  [ + ]   simple_bus            |-- axi
  gpio          0  [   ]   gpio_zynq             |   |-- gpio@e000a000
  i2c           0  [   ]   i2c_cdns              |   |-- i2c@e0004000
  i2c           1  [   ]   i2c_cdns              |   |-- i2c@e0005000
  gpio          1  [   ]   pca953x               |   |   `-- gpio@41
  serial        0  [ + ]   serial_zynq           |   |-- serial@e0000000
  spi           0  [   ]   zynq_qspi             |   |-- spi@e000d000
  spi_flash     0  [   ]   jedec_spi_nor         |   |   `-- flash@0
  blk           0  [   ]   mtd_blk               |   |       |-- [email protected]
  blk           1  [   ]   ubi_blk               |   |       `-- [email protected]
  mmc           0  [ + ]   arasan_sdhci          |   |-- mmc@e0100000
  blk           2  [   ]   mmc_blk               |   |   |-- 
[email protected]
  bootdev       0  [   ]   mmc_bootdev           |   |   `-- 
[email protected]
  simple_bus    1  [ + ]   simple_bus            |   |-- slcr@f8000000
  clk           0  [ + ]   zynq_clk              |   |   `-- clkc@100
  timer         0  [   ]   arm_twd_timer         |   |-- timer@f8f00600
  usb           0  [   ]   ehci_zynq             |   `-- usb@e0002000
  bootstd       0  [   ]   bootstd_drv           `-- bootstd
  bootmeth      0  [   ]   bootmeth_extlinux         `-- extlinux
zynq-uboot> ls mtd 0
** Bad device specification mtd 0 **
Couldn't find partition mtd 0


-- 
Mike Looijmans
System Expert

TOPIC Embedded Products B.V.
Materiaalweg 4, 5681 RJ Best
The Netherlands

T: +31 (0) 499 33 69 69
E: [email protected]
W: www.topic.nl

From 2e822bce1ffeba2b0009e886319383e3eb910a1d Mon Sep 17 00:00:00 2001
From: Mike Looijmans <[email protected]>
Date: Tue, 25 Mar 2025 16:03:03 +0100
Subject: [PATCH] spi/sf_probe.c: Register stuff at ubi/mtd in bind

Doesn't work, see mail list
Creates block devices, but they don't work
Have to set CONFIG_SYS_MALLOC_F_LEN=0x900 to prevent allocation error
---
 drivers/mtd/spi/sf_probe.c  | 27 +++++++++++++++++++++++++++
 include/linux/mtd/spi-nor.h |  3 +++
 2 files changed, 30 insertions(+)

diff --git a/drivers/mtd/spi/sf_probe.c b/drivers/mtd/spi/sf_probe.c
index 7100b64bf22..6a6fc0a9185 100644
--- a/drivers/mtd/spi/sf_probe.c
+++ b/drivers/mtd/spi/sf_probe.c
@@ -7,14 +7,17 @@
  * Copyright (C) 2013 Jagannadha Sutradharudu Teki, Xilinx Inc.
  */
 
+#include <blk.h>
 #include <dm.h>
 #include <errno.h>
+#include <linux/mtd/mtd.h>
 #include <linux/mtd/spi-nor.h>
 #include <log.h>
 #include <malloc.h>
 #include <spi.h>
 #include <spi_flash.h>
 #include <spi-mem.h>
+#include <ubi_uboot.h>
 
 #include "sf_internal.h"
 
@@ -219,6 +222,29 @@ int spi_flash_std_probe(struct udevice *dev)
 	return spi_flash_probe_slave(flash);
 }
 
+int spi_flash_std_bind(struct udevice *dev)
+{
+#ifndef CONFIG_XPL_BUILD
+	struct spi_flash *flash = dev_get_uclass_priv(dev);
+	int ret;
+
+	if (blk_enabled()) {
+		if (CONFIG_IS_ENABLED(MTD_BLOCK)) {
+			// Workaround for mtd_bid requiring a "**" instead of a "*"
+			flash->mtd_p = &flash->mtd;
+			ret = mtd_bind(dev, &flash->mtd_p);
+			if (ret)
+				return ret;
+		}
+
+		if (CONFIG_IS_ENABLED(UBI_BLOCK))
+			return ubi_bind(dev);
+	}
+#endif
+
+	return 0;
+}
+
 static int spi_flash_std_remove(struct udevice *dev)
 {
 	struct spi_flash *flash = dev_get_uclass_priv(dev);
@@ -256,6 +282,7 @@ U_BOOT_DRIVER(jedec_spi_nor) = {
 	.id		= UCLASS_SPI_FLASH,
 	.of_match	= spi_flash_std_ids,
 	.probe		= spi_flash_std_probe,
+	.bind		= spi_flash_std_bind,
 	.remove		= spi_flash_std_remove,
 	.priv_auto	= sizeof(struct spi_nor),
 	.ops		= &spi_flash_std_ops,
diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
index 4eef4ab0488..08b318725bf 100644
--- a/include/linux/mtd/spi-nor.h
+++ b/include/linux/mtd/spi-nor.h
@@ -556,6 +556,9 @@ struct spi_flash {
  */
 struct spi_nor {
 	struct mtd_info		mtd;
+#ifndef CONFIG_XPL_BUILD
+	struct mtd_info		*mtd_p;
+#endif
 	struct udevice		*dev;
 	struct spi_slave	*spi;
 	const struct flash_info	*info;
-- 
2.43.0