gnss: add driver for mediatek receivers

Add driver for serial-connected Mediatek-based GNSS receivers.

These devices typically boot transmitting vendor specific NMEA output
sequences. The serial port bit rate is read from the device tree
"current-speed".

Note that the driver uses the generic GNSS serial implementation and
therefore essentially only manages power abstracted into three power
states: ACTIVE, STANDBY, and OFF.

For mediatek receivers with a main supply and no enable-gpios, this simply
means that the main supply is disabled in STANDBY and OFF (the optional
backup supply is kept enabled while the driver is bound).

Note that the timepulse-support is left unimplemented.

Signed-off-by: Loys Ollivier <lollivier@baylibre.com>
[ johan: rename backup supply ]
Signed-off-by: Johan Hovold <johan@kernel.org>

1 files changed, 13 insertions, 0 deletions

diff --git a/drivers/gnss/Kconfig b/drivers/gnss/Kconfig
index 6abc88514512..6d8c8027e1cd 100644
--- a/drivers/gnss/Kconfig
+++ b/drivers/gnss/Kconfig
@@ -15,6 +15,19 @@ if GNSS
 config GNSS_SERIAL
 	tristate
 
+config GNSS_MTK_SERIAL
+	tristate "Mediatek GNSS receiver support"
+	depends on SERIAL_DEV_BUS
+	select GNSS_SERIAL
+	help
+	  Say Y here if you have a Mediatek-based GNSS receiver which uses a
+	  serial interface.
+
+	  To compile this driver as a module, choose M here: the module will
+	  be called gnss-mtk.
+
+	  If unsure, say N.
+
 config GNSS_SIRF_SERIAL
 	tristate "SiRFstar GNSS receiver support"
 	depends on SERIAL_DEV_BUS