rtc: optee: add RTC driver for OP-TEE RTC PTA

This drivers allows to communicate with a RTC PTA handled by OP-TEE [1].
This PTA allows to query RTC information, set/get time and set/get
offset depending on the supported features.

[1] OP-TEE/optee_os#5179

Signed-off-by: Clément Léger <clement.leger@bootlin.com>
Reviewed-by: Jens Wiklander <jens.wiklander@linaro.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220308133505.471601-1-clement.leger@bootlin.com

Author: clementleger

MAINTAINERS

@@ -14356,6 +14356,12 @@ L:	op-tee@lists.trustedfirmware.org
 S:	Maintained
 F:	drivers/char/hw_random/optee-rng.c
 
+OP-TEE RTC DRIVER
+M:	Clément Léger <clement.leger@bootlin.com>
+L:	linux-rtc@vger.kernel.org
+S:	Maintained
+F:	drivers/rtc/rtc-optee.c
+
 OPA-VNIC DRIVER
 M:	Dennis Dalessandro <dennis.dalessandro@cornelisnetworks.com>
 M:	Mike Marciniszyn <mike.marciniszyn@cornelisnetworks.com>

drivers/rtc/Kconfig

@@ -1293,6 +1293,16 @@ config RTC_DRV_OPAL
 	  This driver can also be built as a module. If so, the module
 	  will be called rtc-opal.
 
+config RTC_DRV_OPTEE
+	tristate "OP-TEE based RTC driver"
+	depends on OPTEE
+	help
+	  Select this to get support for OP-TEE based RTC control on SoCs where
+	  RTC are not accessible to the normal world (Linux).
+
+	  This driver can also be built as a module. If so, the module
+	  will be called rtc-optee.
+
 config RTC_DRV_ZYNQMP
 	tristate "Xilinx Zynq Ultrascale+ MPSoC RTC"
 	depends on OF && HAS_IOMEM

drivers/rtc/Makefile

@@ -115,6 +115,7 @@ obj-$(CONFIG_RTC_DRV_GAMECUBE)	+= rtc-gamecube.o
 obj-$(CONFIG_RTC_DRV_NTXEC)	+= rtc-ntxec.o
 obj-$(CONFIG_RTC_DRV_OMAP)	+= rtc-omap.o
 obj-$(CONFIG_RTC_DRV_OPAL)	+= rtc-opal.o
+obj-$(CONFIG_RTC_DRV_OPTEE)	+= rtc-optee.o
 obj-$(CONFIG_RTC_DRV_PALMAS)	+= rtc-palmas.o
 obj-$(CONFIG_RTC_DRV_PCAP)	+= rtc-pcap.o
 obj-$(CONFIG_RTC_DRV_PCF2123)	+= rtc-pcf2123.o