iio: ltc2983: fix device probe

commit b76d26d upstream.

There is no reason to assume that the IRQ rising edge (indicating that
the device start up phase is done) will happen after we request the IRQ.
If the device is already up by the time we request it, the call to
'wait_for_completion_timeout()' will timeout and we will fail the device
probe even though there's nothing wrong.

Fix it by just polling the status register until we get the indication that
the device is up and running. As a side effect of this fix, requesting the
IRQ is also moved to after the setup function.

Fixes: f110f31 ("iio: temperature: Add support for LTC2983")
Reported-and-tested-by: Drew Fustini <drew@pdp7.com>
Reviewed-by: Drew Fustini <drew@pdp7.com>
Signed-off-by: Nuno Sá <nuno.sa@analog.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Cc: <Stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20210811133220.190264-2-nuno.sa@analog.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/iio/temperature/ltc2983.c

@@ -89,6 +89,8 @@
 
 #define	LTC2983_STATUS_START_MASK	BIT(7)
 #define	LTC2983_STATUS_START(x)		FIELD_PREP(LTC2983_STATUS_START_MASK, x)
+#define	LTC2983_STATUS_UP_MASK		GENMASK(7, 6)
+#define	LTC2983_STATUS_UP(reg)		FIELD_GET(LTC2983_STATUS_UP_MASK, reg)
 
 #define	LTC2983_STATUS_CHAN_SEL_MASK	GENMASK(4, 0)
 #define	LTC2983_STATUS_CHAN_SEL(x) \
@@ -1362,17 +1364,16 @@ static int ltc2983_parse_dt(struct ltc2983_data *st)
 
 static int ltc2983_setup(struct ltc2983_data *st, bool assign_iio)
 {
-	u32 iio_chan_t = 0, iio_chan_v = 0, chan, iio_idx = 0;
+	u32 iio_chan_t = 0, iio_chan_v = 0, chan, iio_idx = 0, status;
 	int ret;
-	unsigned long time;
-
-	/* make sure the device is up */
-	time = wait_for_completion_timeout(&st->completion,
-					    msecs_to_jiffies(250));
 
-	if (!time) {
+	/* make sure the device is up: start bit (7) is 0 and done bit (6) is 1 */
+	ret = regmap_read_poll_timeout(st->regmap, LTC2983_STATUS_REG, status,
+				       LTC2983_STATUS_UP(status) == 1, 25000,
+				       25000 * 10);
+	if (ret) {
 		dev_err(&st->spi->dev, "Device startup timed out\n");
-		return -ETIMEDOUT;
+		return ret;
 	}
 
 	st->iio_chan = devm_kzalloc(&st->spi->dev,
@@ -1492,21 +1493,18 @@ static int ltc2983_probe(struct spi_device *spi)
 	ret = ltc2983_parse_dt(st);
 	if (ret)
 		return ret;
-	/*
-	 * let's request the irq now so it is used to sync the device
-	 * startup in ltc2983_setup()
-	 */
+
+	ret = ltc2983_setup(st, true);
+	if (ret)
+		return ret;
+
 	ret = devm_request_irq(&spi->dev, spi->irq, ltc2983_irq_handler,
 			       IRQF_TRIGGER_RISING, name, st);
 	if (ret) {
 		dev_err(&spi->dev, "failed to request an irq, %d", ret);
 		return ret;
 	}
 
-	ret = ltc2983_setup(st, true);
-	if (ret)
-		return ret;
-
 	indio_dev->name = name;
 	indio_dev->num_channels = st->iio_channels;
 	indio_dev->channels = st->iio_chan;