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SubjectRe: [PATCH] ACPI/Battery: Retry to get Battery information if failed during probing
On Thu, 12 Jun 2014, Lan Tianyu wrote:

> >> Some machines'(E,G Lenovo Z480) ECs are not stable during boot up
> >> and causes battery driver fails to be probed due to failure of getting
> >> battery information from EC sometimes. After several retries, the
> >> operation will work. This patch is to retry to get battery information 5
> >> times if the first try fails.
> >>
> >> Reported-and-tested-by: naszar <naszar@ya.ru>
> >> Reference: https://bugzilla.kernel.org/show_bug.cgi?id=75581
> >> Cc: stable@vger.kernel.org
> >> Signed-off-by: Lan Tianyu <tianyu.lan@intel.com>
> >> ---
> >> drivers/acpi/battery.c | 12 +++++++++++-
> >> 1 file changed, 11 insertions(+), 1 deletion(-)
> >>
> >> diff --git a/drivers/acpi/battery.c b/drivers/acpi/battery.c
> >> index e48fc98..485009d 100644
> >> --- a/drivers/acpi/battery.c
> >> +++ b/drivers/acpi/battery.c
> >> @@ -34,6 +34,7 @@
> >> #include <linux/dmi.h>
> >> #include <linux/slab.h>
> >> #include <linux/suspend.h>
> >> +#include <linux/delay.h>
> >> #include <asm/unaligned.h>
> >>
> >> #ifdef CONFIG_ACPI_PROCFS_POWER
> >> @@ -1119,7 +1120,7 @@ static struct dmi_system_id bat_dmi_table[] = {
> >>
> >> static int acpi_battery_add(struct acpi_device *device)
> >> {
> >> - int result = 0;
> >> + int result = 0, retry = 5;
> >> struct acpi_battery *battery = NULL;
> >>
> >> if (!device)
> >> @@ -1135,7 +1136,16 @@ static int acpi_battery_add(struct acpi_device *device)
> >> mutex_init(&battery->sysfs_lock);
> >> if (acpi_has_method(battery->device->handle, "_BIX"))
> >> set_bit(ACPI_BATTERY_XINFO_PRESENT, &battery->flags);
> >> +
> >> +retry_get_info:
> >> result = acpi_battery_update(battery, false);
> >> +
> >> + if (result && retry) {
> >> + msleep(20);
> >
>
> Hi David:
> Thanks for review.
>
> > We're really going to wait up to 20 * 5 = 100ms for acpi_battery_update()
> > to succeed?
>
> No, this depends which retry acpi_battery_update() will succeed. For
> most machines, there will be no delay.
>

Right, but you're willing to wait up to 100ms for it to succeed? You're
implementing x retries with y ms sleep in between, I'm asking how it is
determined that the optimal values are x = 5 and y = 20. More directly:
is it possible to succeed at 101ms? Is it really likely to succeed after
the first 20ms?


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