add support for ST M41T94 SPI RTC (patch rev. 3)

This patch adds kernel driver for M41T94 RTC chip connected via SPI. I've tested it on two different AT91-based hardwares.

This is third revision of the patch: some comments made by Alessandro Zummo fixed.

Revision two added support for century bit and fixes.

diff -urN orig/drivers/rtc/Kconfig linux-2.6.25/drivers/rtc/Kconfig
@@ -266,6 +266,15 @@
 
 if SPI_MASTER
 
+config RTC_DRV_M41T94
+	tristate "ST M41T94"
+	help
+	  If you say yes here you will get support for the
+	  ST M41T94 SPI RTC chip.
+
+	  This driver can also be built as a module. If so, the module
+	  will be called rtc-m41t94.
+
 config RTC_DRV_MAX6902
 	tristate "Maxim MAX6902"
 	help

diff -urN orig/drivers/rtc/Makefile linux-2.6.25/drivers/rtc/Makefile
@@ -33,6 +33,7 @@
 obj-$(CONFIG_RTC_DRV_EP93XX)	+= rtc-ep93xx.o
 obj-$(CONFIG_RTC_DRV_ISL1208)	+= rtc-isl1208.o
 obj-$(CONFIG_RTC_DRV_M41T80)	+= rtc-m41t80.o
+obj-$(CONFIG_RTC_DRV_M41T94)	+= rtc-m41t94.o
 obj-$(CONFIG_RTC_DRV_M48T59)	+= rtc-m48t59.o
 obj-$(CONFIG_RTC_DRV_M48T86)	+= rtc-m48t86.o
 obj-$(CONFIG_RTC_DRV_MAX6900)	+= rtc-max6900.o

[ I sent a few private messages to Kim, but I'll sumarize my problem here ]

Hi all,

I have AT91SAM9260-based board, kernel is 2.6.26.3. M41T94 is connected on SPI channel 1, chip select 0. I've applied Kim's patch and added SPI device in board-sam9260ek.c:

#if defined(CONFIG_RTC_DRV_M41T94) || defined(CONFIG_RTC_DRV_M41T94_MODULE)
	{	/* External RTC */
		.modalias	= "rtc-m41t94",
		.chip_select	= 0,
		.max_speed_hz	= 2 * 1000 * 1000,
		.bus_num	= 1,
	},

#endif

During booting up everything seems fine (M41T94 is found etc), but it is not working. Here is some output:

rtc-m41t94: dev (254:0)
rtc-m41t94 spi1.0: rtc core: registered rtc-m41t94 as rtc0 rtc-m41t94 spi1.0: read secs=0, mins=0, hours=0, mday=0, mon=-1, year=100, wday=-1
rtc-m41t94 spi1.0: hctosys: unable to read the hardware clock [..]

# hwclock -r;dmesg
hwclock: RTC_RD_TIME: Invalid argument
rtc-m41t94 spi1.0: read secs=0, mins=0, hours=0, mday=0, mon=-1,
year=100, wday=-1

#hwclock -w;dmesg
rtc-m41t94 spi1.0: write secs=15, mins=0, hours=0, mday=1, mon=0, year=70, wday=4

I've tried both SPIMODE0 and SPIMODE3 (according to m41t94 datasheet) but no improvements.

Thanks

I'm using my RTC-patch with the same CPU. Custom AT91SAM9260 board, external RTC because of AT's errata...

I'm using it with ".max_speed_hz = 1 * 1000 * 1000," instead of 2 MHz. Can you try with slower speed? My patch (rev 3) and this small ek_spi_devices[] modification should be enough.

I have it on bus = 0, chip_select = 1, so I've also removed dataflash parts from ek_spi_devices[] (we're using NOR flash). But for you this is not needed.

I also have a patch to add support for M41T94's watchdog timer. It's not clean enough to be submitted upstreams yet. If you need it I can email it to you.