Reading from SPI flash more than 35 bytes causes driver timeout and results to corrupt

Question

I have connected SPI flash to my linux board (imx 233 based) running in it's SPI bus. I have configured kernel, and SPI bus and flash chip to it.

The flash is currently on a breadboard. Before trying to work on linux, I tried separately and I'm able to read and write as I like with a FT2232H chip (FT2232 breakout board by dangerousprototypes.com). However, linux-board, I had to add pull-up resistors (10k) in the data in and data out lines, the chip was not recognized correctly otherwise.

My actual problem is that now I'm trying to just read raw flash through mtd driver, and everything seems correct, if I read less than 35 bytes. Immediately if I read more than 35 bytes (36 or more), the driver complains about DMA error:

[  521.700000] mxs-spi 80034000.ssp: DMA transfer timeout
[  521.700000] spi_master spi32766: failed to transfer one message from queue

Also when this happens, most of (if not all) the bytes will be incorrect.. Reading less than 35 bytes will return "immediately" (no timeout), and all bytes read will be correct.

My C code is straight from MTD read example:

int main(int argc, char * argv[])
{

    if (argc != 2)
    {
    printf("Need arguments how many chars to read\nExiting...\n");
    return 1;
    }

    int amount = atoi(argv[1]);
    printf("reading (%d) chars\n", amount);

    mtd_info_t mtd_info;
    int fd = open("/dev/mtd0", O_RDONLY);
    ioctl(fd, MEMGETINFO, &mtd_info);

    printf("MTD type: %u\n", mtd_info.type);
    printf("MTD total size : %u bytes\n", mtd_info.size);
    printf("MTD erase size : %u bytes\n", mtd_info.erasesize);

    /* read buffer */
    unsigned char buf[amount];

    read(fd, buf, sizeof(buf));

    int i = 0;

    for (i = 0; i < amount; i++)
    {
            printf("%i: %X\n",i,buf[i]);
    }
return 0;
} 

The timeout happens "as expected" (10 seconds) in spi-mxs.c:

drivers/spi/spi-msx.c:
static int mxs_spi_txrx_dma(...):
....
ret = wait_for_completion_timeout(&spi->c, msecs_to_jiffies(SSP_TIMEOUT));

Any ideas what might be wrong ? I'm not that good with electronics, so please all suggestions are welcome.

Answer 1

I think it is a problem with the SPI driver. Does it still not work with 3.7 upstream kernel? There were a lot of fixes applied there.

Answer 2

This is not an electronics problem. On a SPI bus, the master is in complete control of the timing of any transfer that is initiated. In particular, on a read operation, the slave device can return bad data or no data at all, but it can't affect whether or not the transfer completes.

In other words, the DMA timeout error you're getting is entirely an issue within the Linux kernel or the specific driver you're using. In any case, a more specific answer is going to require a lot more detail from you: What flash chip are you using? What CPU board are you using? What Linux distribution are you using? What are the version numbers of the kernel and any kernel modules and/or device drivers you're using? Do you have links to where these items can be found?