On 14/03/2014 06:39, Lan Tianyu wrote:
2014-03-12 6:20 GMT+08:00 Matthew Garrett <matthew.garrett@xxxxxxxxxx>:
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.
Hi Matthew:
This patch is to avoid a redundant battery select operation when
the battery is selected. But the symptom "bus timeouts" is a bus transaction
issue, right? Will this happen during other SBS write/read operations? Do we
need to increase the wait time of SMBUS transaction?
Well, the patch does the job and is needed on a macbook air.
What should we test to make it potentially better?
Signed-off-by: Matthew Garrett <matthew.garrett@xxxxxxxxxx>
---
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
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