[v3,6/6] sc16is7xx: Read the LSR register for basic device presence check

Message ID 20200521091152.404404-7-daniel@zonque.org
State New
Headers show
Series
  • [v3,1/6] dt-bindings: sc16is7xx: Add flag to activate IrDA mode
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Commit Message

Daniel Mack May 21, 2020, 9:11 a.m.
Currently, the driver probes just fine and binds all its resources even
if the physical device is not present.

As the device lacks an identification register, let's at least read the
LSR register to check whether a device at the configured address responds
to the request at all.

Signed-off-by: Daniel Mack <daniel@zonque.org>
---
 drivers/tty/serial/sc16is7xx.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

Patch

diff --git a/drivers/tty/serial/sc16is7xx.c b/drivers/tty/serial/sc16is7xx.c
index 7e2360f8e393..5e84ed5938af 100644
--- a/drivers/tty/serial/sc16is7xx.c
+++ b/drivers/tty/serial/sc16is7xx.c
@@ -1181,6 +1181,7 @@  static int sc16is7xx_probe(struct device *dev,
 {
 	struct sched_param sched_param = { .sched_priority = MAX_RT_PRIO / 2 };
 	unsigned long freq = 0, *pfreq = dev_get_platdata(dev);
+	unsigned int val;
 	u32 uartclk = 0;
 	int i, ret;
 	struct sc16is7xx_port *s;
@@ -1188,6 +1189,16 @@  static int sc16is7xx_probe(struct device *dev,
 	if (IS_ERR(regmap))
 		return PTR_ERR(regmap);
 
+	/*
+	 * This device does not have an identification register that would
+	 * tell us if we are really connected to the correct device.
+	 * The best we can do is to check if communication is at all possible.
+	 */
+	ret = regmap_read(regmap,
+			  SC16IS7XX_LSR_REG << SC16IS7XX_REG_SHIFT, &val);
+	if (ret < 0)
+		return ret;
+
 	/* Alloc port structure */
 	s = devm_kzalloc(dev, struct_size(s, p, devtype->nr_uart), GFP_KERNEL);
 	if (!s) {