spi can't read more than 64 bytes

Moti Cohen motic.mail at gmail.com
Wed Jul 6 09:25:59 EDT 2016

Hi all,

I'm trying to write a kernel device driver for a Freescale imx6 processor
based board.

This driver is using spi to communicate with a radio module (using linux

I managed to wr/rd from the module, however once I'm trying to read more
than 64 bytes I'm getting coruppted data. here are some details:

The SPI reading process goes as follows:

1.      Interrupt function is invoked from SPI device via dedicated
GPIO line.

2.       The interrupt function performs asynchronous SPI read in
the following order:

2.1   radio_trx_end_callback is called, as it is the registered call
back function.

2.2   radio_trx_end_callback calls hal_frame_read function which prepares
spi_message and spi_transfer structures and fill them with relevant data:
spi_device , data tx, transfer len , complete handler , …

3.      The read itself  is done by calling to function spi_async

4.      The completion handler function is called and prints the
read message, but trying to read more than 64 bytes in one transaction
causes the read data to be corrupted.

Any idea why am I seeing this behavior ?

Is there (in Linux) any definition for the size to be read via the SPI ?

The relevant variables and functions can be seen below:

Thanks in advance for helping..


uint8_t rx_buf[200];

uint8_t reg[200] = {HAL_TRX_CMD_FR, 0xff, 0xff};

struct spi_transfer transfer;

struct spi_message  spi_msg;

// interrupt function


static irq_handler_t radio_trx_end_callback(unsigned int irq, void *dev_id,
struct pt_regs *regs)


    hal_frame_read(irq, dev_id);

    return (irq_handler_t) IRQ_HANDLED;      // Announce that the IRQ has
been handled correctly


//read function


void hal_frame_read(unsigned int irq, void *dev_id)


        int status;

        spi_device->irq = irq;


        spi_msg.spi = spi_device;

        spi_msg.complete = rf_rx_completion_handler;

        spi_msg.context = NULL;

        memset((uint8_t*)&transfer, 0, sizeof(transfer));

        memset(rx_buf, 0xFF, sizeof(rx_buf));

        memset(reg, 0xFF, sizeof(reg));

        reg[0] = HAL_TRX_CMD_FR;

        transfer.tx_buf = reg;

        transfer.len =64;

        transfer.rx_buf = rx_buf;

        spi_message_add_tail(&transfer, &spi_msg);

        memset(rx_buf, 0x0, sizeof(rx_buf));

        status = spi_async(spi_device, &spi_msg);



//read completion handler


static void rf_rx_completion_handler(void *arg)


        int ii;

//print the received message

printk("\npure message: rx_buf [1]-2=%02X\n      ", rx_buf [1]-2);

        for (ii=0; ii< rx_buf [1]-2; ii++)

                        printk("%02X ", rx_buf [2+ii]);

        printk("\nframe len=%X actual len=%X
status=%i\n",spi_msg.frame_length, spi_msg.actual_length, spi_msg.status);


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