Dear All,
I'm having trouble understanding the difference between spi_sync and spi_async:
Theoretically, spi_sync waits for completion while spi_async provides
completion callbacks. However, on my platform spi_async does not do anything!
I have the following code that is supposed to write a single byte. Using
spi_sync works fine, calling the completion callback with spi_async also works.
I just do not see anything on the connected oscilloscope screen.
What am I missing?
Thanks in advance
Moritz
int lprf_set_WREN(void)
{
int status, ret;
int sync = 0;
struct spi_message m;
struct spi_transfer t;
u8 *buffer = kmalloc(sizeof(u8), GFP_KERNEL);
memset(buffer, 0, sizeof(u8));
buffer[0] = 0x06;
t.tx_buf = buffer;
t.rx_buf = NULL;
printk(KERN_DEBUG "lprf: buffer=%p\n", buffer);
t.len = 1;
t.bits_per_word = 0;
spi_message_init(&m);
spi_message_add_tail(&t, &m);
printk(KERN_DEBUG "lprf: lprf_set_WREN start\n");
if (sync) {
/* Variante A: sync */
status = spi_sync(lp->spi, &m);
printk(KERN_DEBUG "lprf: lprf_set_WREN sync end. status=%d \n",
status);
} else {
/* Variante B: async */
init_completion(&lp->state_complete);
m.complete = lprf_mycomplete;
m.context = &lp->state_complete;
ret = spi_myvalidate(lp->spi, &m);
if (ret) {
printk(KERN_DEBUG "spi_myvalidate returned %d\n", ret);
return ret;
}
status = spi_async_locked(lp->spi, &m);
if (status == 0) {
wait_for_completion(&lp->state_complete);
status = m.status;
}
printk(KERN_DEBUG "lprf: lprf_set_WREN async end status=%d
m.status=%d\n",
status, m.status);
m.context = NULL;
}
if (status)
printk(KERN_ERR "lprf: spi_async failed at %s, %i\n", __FILE__,
__LINE__);
return status;
}
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