linux-kernel - Re: [PATCH] ACPI/Battery: Retry to get Battery information if failed during probing

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Message-ID: <alpine.DEB.2.02.1406120025050.23724@chino.kir.corp.google.com>
Date:	Thu, 12 Jun 2014 00:26:47 -0700 (PDT)
From:	David Rientjes <rientjes@...gle.com>
To:	Lan Tianyu <tianyu.lan@...el.com>
cc:	rjw@...ysocki.net, lenb@...nel.org, naszar@...ru,
	linux-acpi@...r.kernel.org, linux-kernel@...r.kernel.org,
	stable@...r.kernel.org
Subject: Re: [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@...ru>
> >> Reference: https://bugzilla.kernel.org/show_bug.cgi?id=75581
> >> Cc: stable@...r.kernel.org
> >> Signed-off-by: Lan Tianyu <tianyu.lan@...el.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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