Re: Trying to get MTD_BLOCK to actually work

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.

The mailing list has moved to [email protected].

Please, use scripts/get_maintainer.pl to find the maintainer of a 
specific U-Boot module.

Best regards

Heinrich

> 
> Example session:
> 
> zynq-uboot> mtd list
> SF: Detected n25q256ax1 with page size 256 Bytes, erase size 64 KiB, 
> total 32 MiB
> 0x000000000000-0x000000100000 : "qspi-boot-bin"
> 0x000000100000-0x000002000000 : "qspi-rootfs"
> List of MTD devices:
> * nor0
>    - device: flash@0
>    - parent: spi@e000d000
>    - driver: jedec_spi_nor
>    - path: /axi/spi@e000d000/flash@0
>    - type: NOR flash
>    - block size: 0x10000 bytes
>    - min I/O: 0x1 bytes
>    - 0x000000000000-0x000002000000 : "nor0"
>            - 0x000000000000-0x000000100000 : "qspi-boot-bin"
>            - 0x000000100000-0x000002000000 : "qspi-rootfs"
> zynq-uboot> lsblk
> Block Driver          Devices
> -----------------------------
> mmc_blk             : mmc 0
> mtd_blk             : <none>
> ubi_blk             : <none>
> 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
>   mmc           0  [ + ]   arasan_sdhci          |   |-- mmc@e0100000
>   blk           0  [   ]   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
> 
>