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SubjectRe: [PATCH 3/3] ACPI: Don't re-select SBS battery if it's already selected
On 14/03/2014 06:39, Lan Tianyu wrote:
> 2014-03-12 6:20 GMT+08:00 Matthew Garrett <matthew.garrett@nebula.com>:
>> 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@nebula.com>
>> ---
>> 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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>
>



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