spi: davinci: Adapt transfer's timeout to transfer's length

The timeout used when waiting for transfer's completion is always set to
HZ. This isn't enough if a transfer is too large or if the bus speed is
too low.

Use the bus speed and the transfer length to calculate an appropriate
timeout

Signed-off-by: Bastien Curutchet <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Mark Brown <[e-mail]>

drivers/spi/spi-davinci.c

···
 	u32 errors = 0;
 	struct davinci_spi_config *spicfg;
 	struct davinci_spi_platform_data *pdata;
+	unsigned long timeout;
 
 	dspi = spi_controller_get_devdata(spi->controller);
 	pdata = &dspi->pdata;
···
 
 	/* Wait for the transfer to complete */
 	if (spicfg->io_type != SPI_IO_TYPE_POLL) {
-		if (wait_for_completion_timeout(&dspi->done, HZ) == 0)
+		timeout = DIV_ROUND_UP(t->speed_hz, MSEC_PER_SEC);
+		timeout = DIV_ROUND_UP(t->len * 8, timeout);
+		/* Assume we are at most 2x slower than the nominal bus speed */
+		timeout = 2 * msecs_to_jiffies(timeout);
+
+		if (wait_for_completion_timeout(&dspi->done, timeout) == 0)
 			errors = SPIFLG_TIMEOUT_MASK;
 	} else {
 		while (dspi->rcount > 0 || dspi->wcount > 0) {