linux-kernel - Re: [PATCH 3/3] ACPI: Don't re-select SBS battery if it's already selected

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Date:	Mon, 11 Aug 2014 13:14:44 +0200
From:	"xavier.gnata@...il.com" <xavier.gnata@...il.com>
To:	Lan Tianyu <lantianyu1986@...il.com>,
	Matthew Garrett <matthew.garrett@...ula.com>
CC:	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	"linux-kernel@...r kernel org" <linux-kernel@...r.kernel.org>,
	Len Brown <lenb@...nel.org>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>
Subject: Re: [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@...ula.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@...ula.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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