Getting EINVAL when trying to write to mtd device

Question

I am referring to the code in this answer. I added error handling though. The open() erase and the read() all perform without error and the 20 bytes that I read all are 0xff. However, when trying to write the 20 bytes from the data[] array, I get an EINVAL errorcode from the write() function. What could be the cause of the problem? I did erase the memory before trying to write...

Saurian

Can you give some more information about the system you are attempting to do this on? – Clergy

It's a linux kernel 3.6.9 on a custom board with an ARM Cortex-A5 and 128MB of NAND Flash. – Saurian

That answer explains possible causes for EINVAL - have you eliminated all of those reasons? – Brander

Answer 1

I have seen your original post. I have the same problem recently, and I found that the write size is important.

mtd_info_t(struct mtd_info_user) have a variable named writesize (reference: https://elixir.bootlin.com/linux/v3.2/source/include/mtd/mtd-abi.h#L125)

struct mtd_info_user {
    __u8 type;
    __u32 flags;
    __u32 size; /* Total size of the MTD */
    __u32 erasesize;
    __u32 writesize;
    __u32 oobsize;  /* Amount of OOB data per block (e.g. 16) */
    __u64 padding;  /* Old obsolete field; do not use */
};

when write to the mtd, should notice writesize

#include <fcntl.h>
#include <mtd/mtd-user.h>
#include <stdio.h>
#include <stdint.h>
#include <string.h>
#include <sys/ioctl.h>

int main(){
    mtd_info_t mtd_info;           // the MTD structure
    erase_info_t ei;               // the erase block structure
    int i;

    unsigned char read_buf[20] = {0x00};                // empty array for reading

    int fd = open("/dev/mtd0", O_RDWR); // open the mtd device for reading and 
                                        // writing. Note you want mtd0 not mtdblock0
                                        // also you probably need to open permissions
                                        // to the dev (sudo chmod 777 /dev/mtd0)

    ioctl(fd, MEMGETINFO, &mtd_info);   // get the device info

    // dump it for a sanity check, should match what's in /proc/mtd
    printf("MTD Type: %x\nMTD total size: %x(hex) bytes\nMTD erase size: %x(hex) bytes\nMTD write size: %x(hex) bytes\n",
        mtd_info.type, mtd_info.size, mtd_info.erasesize, mtd_info.writesize);

    ei.length = mtd_info.erasesize;   //set the erase block size
    for(ei.start = 0; ei.start < mtd_info.size; ei.start += ei.length)
    {
        ioctl(fd, MEMUNLOCK, &ei);
        // printf("Eraseing Block %#x\n", ei.start); // show the blocks erasing
                                                  // warning, this prints a lot!
        ioctl(fd, MEMERASE, &ei);
    }    

    lseek(fd, 0, SEEK_SET);               // go to the first block
    read(fd, read_buf, sizeof(read_buf)); // read 20 bytes

    // sanity check, should be all 0xFF if erase worked
    for(i = 0; i<20; i++)
        printf("buf[%d] = 0x%02x\n", i, (unsigned int)read_buf[i]);

    /**********************************************************
     *   important part!                                      *
     *   notice the size of data array is mtd_info.writesize  *
     **********************************************************/
    uint32_t write_size = mtd_info.writesize;
    unsigned char data[write_size];//write 0
    bzero(data, write_size);

    lseek(fd, 0, SEEK_SET);        // go back to first block's start
    write(fd, data, sizeof(data)); // write our message

    lseek(fd, 0, SEEK_SET);              // go back to first block's start
    read(fd, read_buf, sizeof(read_buf));// read the data

    // sanity check, now you see the message we wrote!    
    for(i = 0; i<20; i++)
        printf("buf[%d] = 0x%02x\n", i, (unsigned int)read_buf[i]);

    close(fd);
    return 0;
}

Hope it can help

Diantha

Answer 2

From ./drivers/mtd/nand/nand_base.c

#define NOTALIGNED(x) ((x & (chip->subpagesize - 1)) != 0)

This is the check performed by driver:

/* Reject writes, which are not page aligned */
if (NOTALIGNED(to) || NOTALIGNED(ops->len)) {
    pr_notice("%s: attempt to write non page aligned data\n",__func__);
return -EINVAL;
}

Both the address you are starting the write and and length of the buffer you are writing must satisfy the macro condition(to be multiple of the subpage size).

Cloudburst