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ACPI: Don't re-select SBS battery if it's already selected

Message ID 1394481134-1723-1-git-send-email-matthew.garrett@nebula.com (mailing list archive)
State Superseded, archived
Headers show

Commit Message

Matthew Garrett March 10, 2014, 7:52 p.m. UTC 
The existing SBS code explicitly sets the selected battery in the SBS
manager regardless of whether the battery in question is already selected.
This causes bus timeouts on Apple hardware. Check for this case and avoid
it.

Signed-off-by: Matthew Garrett <matthew.garrett@nebula.com>
---
 drivers/acpi/sbs.c | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)
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Patch

diff --git a/drivers/acpi/sbs.c b/drivers/acpi/sbs.c
index dbd4849..c386505 100644
--- a/drivers/acpi/sbs.c
+++ b/drivers/acpi/sbs.c
@@ -470,17 +470,25 @@  static struct device_attribute alarm_attr = {
 static int acpi_battery_read(struct acpi_battery *battery)
 {
 	int result = 0, saved_present = battery->present;
-	u16 state;
+	u16 state, selected, desired;
 
 	if (battery->sbs->manager_present) {
 		result = acpi_smbus_read(battery->sbs->hc, SMBUS_READ_WORD,
 				ACPI_SBS_MANAGER, 0x01, (u8 *)&state);
 		if (!result)
 			battery->present = state & (1 << battery->id);
-		state &= 0x0fff;
-		state |= 1 << (battery->id + 12);
-		acpi_smbus_write(battery->sbs->hc, SMBUS_WRITE_WORD,
-				  ACPI_SBS_MANAGER, 0x01, (u8 *)&state, 2);
+		/*
+		 * Don't switch battery if the correct one is already selected
+		 */
+		selected = state & 0xf000;
+		desired = 1 << (battery->id + 12);
+		if (selected != desired) {
+			state &= 0x0fff;
+			state |= desired;
+			acpi_smbus_write(battery->sbs->hc, SMBUS_WRITE_WORD,
+					 ACPI_SBS_MANAGER, 0x01,
+					 (u8 *)&state, 2);
+		}
 	} else if (battery->id == 0)
 		battery->present = 1;
 	if (result || !battery->present)