>From 2a8ffff11f91aad146916ca14c768ebc407865aa Mon Sep 17 00:00:00 2001 From: Matthew Garrett Date: Mon, 10 Mar 2014 14:44:55 -0400 Subject: [PATCH 21/28] ACPI: Don't re-select SBS battery if it's already selected 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 --- drivers/acpi/sbs.c | 18 +++++++++++++----- 1 file changed, 13 insertions(+), 5 deletions(-) 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) -- 1.8.5.3