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?
> 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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--
Best regards
Tianyu Lan
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