OT200: reset MFGTP7 (backlight pwm)

The CS5536 companion device has three different power domains.
* working domain
* standby domain
* RTC domain

When the system is "off" only the standby domain is powered.
MFGPT[7:6] are member of the standby power domain.

MFGPT7 is used to control the backlight of the device and so the
timer gets used and configured during system boot. If the system
does a reboot the timer stays configured and the Linux driver
can not use it:
   "ot200-backlight: ot200-backlight.0: MFGPT 7 not availale"

The cs5535-mfgpt has a function to hard-reset all MFGPTs but the
system hangs after the first access to a MFGPT register - cause
unknown.

/*
 * This is a sledgehammer that resets all MFGPT timers. This is required by
 * some broken BIOSes which leave the system in an unstable state
 * (TinyBIOS 0.98, for example; fixed in 0.99).  It's uncertain as to
 * whether or not this secret MSR can be used to release individual timers.
 * Jordan tells me that he and Mitch once played w/ it, but it's unclear
 * what the results of that were (and they experienced some instability).
 */
static void reset_all_timers(void)
{
	uint32_t val, dummy;

	/* The following undocumented bit resets the MFGPT timers */
	val = 0xFF; dummy = 0;
	wrmsr(MSR_MFGPT_SETUP, val, dummy);
}

After playing around with this undocumented MSR it looks like I only
need to set bit 7 to free the MFGPT7.

BTW, all MFGPT[0:5] will be reset during pll_reset().

Change-Id: I54a8d479ce495b0fc2f54db766a8d793bbb5d704
Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Reviewed-on: http://review.coreboot.org/2527
Tested-by: build bot (Jenkins)
Reviewed-by: Jens Rottmann <JRottmann@LiPPERTembedded.de>
Reviewed-by: Paul Menzel <paulepanter@users.sourceforge.net>
Reviewed-by: Marc Jones <marc.jones@se-eng.com>

1 files changed, 8 insertions, 0 deletions

diff --git a/src/mainboard/bachmann/ot200/mainboard.c b/src/mainboard/bachmann/ot200/mainboard.c
index ac6855ac00..0ea053aad0 100644
--- a/src/mainboard/bachmann/ot200/mainboard.c
+++ b/src/mainboard/bachmann/ot200/mainboard.c
@@ -21,6 +21,7 @@
 #include <device/smbus.h>
 #include <smbios.h>
 #include <console/console.h>
+#include <cpu/x86/msr.h>
 
 /* overwrite a weak function to fill SMBIOS table with a custom value */
 static u8 hw_rev = 0;
@@ -43,6 +44,7 @@ static void init(struct device *dev)
 	unsigned int i;
 	u32 chksum = 0;
 	char block[20];
+	msr_t reset;
 	device_t eeprom_dev = dev_find_slot_on_smbus(1, 0x52);
 
 	if (eeprom_dev == 0) {
@@ -63,6 +65,12 @@ static void init(struct device *dev)
 	hw_rev = block[5];
 
 	printk(BIOS_DEBUG, "hw revision: %u\n", hw_rev);
+
+	/* Reset MFGPT7 (standby power domain) - this is done via
+	 * an undocumented register */
+	reset = rdmsr(0x5140002b);
+	reset.lo |= 1 << 7;
+	wrmsr(0x5140002b, reset);
 }
 
 static void mainboard_enable(struct device *dev)