linux device driver - ADS1292R problem in reading chip id on spi - linux-device-driver

Question

I am novice to Linux device driver and writing driver module for TI-ADS1292R chip. This driver is loading without any error, creates character device entry in /dev directory. I am also able to transfer data on SPI bus (verified it on logic analyzer and DSO).
There are two problems here.
(1) in logic analyzer it shows that chip is responding with correct chip id (0x73) on read id command, but in my driver I am getting incorrect value (0x80). Why this is happening and where the problem is?
(2) As far as I understood, my driver should automatically loaded if I have configured it through defconfig file, which is not happening in my case. Right now, I am loading it as a built-in module with obj-y option.
My code has following snippets through which I am trying to read the chip id.
static int ads_send_byte(struct ads1292_chip *dev, int data)
{
int status;
struct spi_message msg = { };
struct spi_transfer transfer = { };
dev->tx_buff[0] = data;
transfer.tx_buf = dev->tx_buff;
transfer.rx_buf = dev->rx_buff;
transfer.len = 1;
transfer.speed_hz = SPI_BUS_SPEED;
spi_message_init(&msg);
spi_message_add_tail(&transfer, &msg);
status = spi_sync(dev->spi, &msg);
printk(KERN_DEBUG "ecg: %s (%#x) %d\n", __func__, data, status);
return status;
};
static int ads_send_RREG(struct ads1292_chip *dev, char __user * buf, u8 reg, u8 size)
{
struct spi_message msg = { };
struct spi_transfer transfer = { };
int ret;
dev->tx_buff[0] = ADS1292_RREG | reg;
dev->tx_buff[1] = size - 1; // datasheet: no of regs - 1
memset(dev->rx_buff, 0, size);
memset(dev->tx_buff + 2, 0, size);
transfer.speed_hz = SPI_BUS_SPEED;
transfer.tx_buf = dev->tx_buff;
transfer.rx_buf = dev->rx_buff;
transfer.len = size + 2; // 2 is for command tx
transfer.delay_usecs = 40; // datasheet: 4 clocks after each message
transfer.cs_change = 1; // Always toggle CS line after transfer
spi_message_init(&msg);
spi_message_add_tail(&transfer, &msg);
ret = spi_sync(dev->spi, &msg);
//printk(KERN_DEBUG "ecg: %s %x\n", __func__, dev->rx_buff[0]);
if (unlikely(ret))
return ret;
ret = copy_to_user(buf, dev->rx_buff, size);
return ret;
}
static int ads_cdev_open(struct inode *inode, struct file *filp)
{
struct ads1292_dev *ads = container_of(inode->i_cdev, struct ads1292_dev, dev);
char buff[1];
printk(KERN_DEBUG "ecg: %s\n", __func__);
filp->private_data = ads;
gpio_set_value_cansleep(ads1292_gpio_start.gpio, 0);
ads_send_byte(&ads->chip, ADS1292_RESET);
mdelay(1);
ads_send_byte(&ads->chip, ADS1292_SDATAC);
mdelay(10);
ads_send_RREG(&ads->chip, buff, ADS1292_ID, 1);
printk(KERN_DEBUG "ecg: ID - %x\n", buff[0]);
return 0;
}