hp/pavilion_m6_1035dx: Shutdown on low battery with non-ACPI OS

Intercept the low battery SMI from the EC, and shut down the system
immediately. The EC only sends this SMI when the OS did not enable
ACPI mode, so ACPI OSes are not affected by this.
On the other hand, payloads such as GRUB or SeaBIOS will experience
the shutdown. This behavior is helpful for protecting the battery, for
example, when the OS fails to boot and we are stuck in the payload.
The low battery SMI is triggered at 10% charge, at which point the risk
of cell degradation exists.

Change-Id: I4c6c1a4feed8576cbdbb1945768de0805a1f5e42
Signed-off-by: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Reviewed-on: http://review.coreboot.org/5527
Tested-by: build bot (Jenkins)
Reviewed-by: Aaron Durbin <adurbin@gmail.com>

src/mainboard/hp/pavilion_m6_1035dx/mainboard_smi.c

@@ -6,14 +6,26 @@
  */
 #include "ec.h"
 
+#include <arch/io.h>
 #include <console/console.h>
 #include <cpu/x86/smm.h>
 #include <delay.h>
 #include <ec/compal/ene932/ec.h>
 #include <southbridge/amd/agesa/hudson/hudson.h>
 
+#define ACPI_PM1_CNT_SLEEP(state) ((1 << 13) | (state & 0x7) << 10)
+
+enum sleep_states {
+	S0 = 0,
+	S1 = 1,
+	S3 = 3,
+	S4 = 4,
+	S5 = 5,
+};
+
 enum ec_smi_event {
 	EC_SMI_EVENT_IDLE = 0x80,
+	EC_SMI_BATTERY_LOW = 0xb3,
 };
 
 /* Tell EC to operate in APM mode. Events generate SMIs instead of SCIs */
@@ -37,13 +49,19 @@ static uint8_t ec_get_smi_event(void)
 
 static void ec_process_smi(uint8_t src)
 {
-	/*
-	 * Stub: We aren't processing any events yet, but reading the SMI source
-	 * satisfies the EC in terms of responding to the event.
+	/* Reading the SMI source satisfies the EC in terms of responding to
+	 * the event, regardless of whether we take an action or not.
 	 */
 
+	switch (src) {
+	case EC_SMI_BATTERY_LOW:
+		printk(BIOS_DEBUG, "Battery low. Shutting down\n");
+		outl(ACPI_PM1_CNT_SLEEP(S5), ACPI_PM1_CNT_BLK);
+		break;
+	default:
 		printk(BIOS_DEBUG, "EC_SMI event 0x%x\n", src);
 	}
+}
 
 static void handle_ec_smi(void)
 {