linux-kernel - Re: [PATCH] regulator: MAX8997: Fix for divide by zero error

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Message-ID: <4E016012.8090406@linaro.org>
Date:	Wed, 22 Jun 2011 08:52:58 +0530
From:	Tushar Behera <tushar.behera@...aro.org>
To:	myungjoo.ham@...sung.com
CC:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linaro-dev@...ts.linaro.org" <linaro-dev@...ts.linaro.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"lrg@...com" <lrg@...com>,
	"broonie@...nsource.wolfsonmicro.com" 
	<broonie@...nsource.wolfsonmicro.com>,
	박경민 <kyungmin.park@...sung.com>,
	Samuel Ortiz <sameo@...ux.intel.com>
Subject: Re: [PATCH] regulator: MAX8997: Fix for divide by zero error

On Wednesday 22 June 2011 08:18 AM, 함명주 wrote:
> Sender : Tushar Behera<tushar.behera@...aro.org>
> Date : 2011-06-21 12:38 (GMT+09:00)
>> Currently, ramp_delay variable is used uninitialized in
>> max8997_set_voltage_ldobuck which gets called through
>> regulator_register calls.
>>
>> To fix the problem, in max8997_pmic_probe, ramp_delay initialization
>> code is moved before calls to regulator_register.
>>
>> Cc: Liam Girdwood
>> Cc: Mark Brown
>> Cc: MyungJoo Ham
>> Cc: Kyungmin Park
>> Cc: Samuel Ortiz
>> Signed-off-by: Tushar Behera
> 
> Although I've never been reported such an issue, but I'm sure this will cause one any time. Thanks!
One scenario:
Division by zero in kernel.
[<c00399c4>] (unwind_backtrace+0x0/0xe0) from [<c0162ed4>] (Ldiv0+0x8/0x10)
[<c0162ed4>] (Ldiv0+0x8/0x10) from [<c018a1bc>]
(max8997_set_voltage_ldobuck+0x198/0x1bc)
[<c018a1bc>] (max8997_set_voltage_ldobuck+0x198/0x1bc) from [<c0187ae8>]
(_regulator_do_set_voltage+0x2c/0x1c4)
[<c0187ae8>] (_regulator_do_set_voltage+0x2c/0x1c4) from [<c0187eec>]
(regulator_register+0x25c/0xe2c)
[<c0187eec>] (regulator_register+0x25c/0xe2c) from [<c02b9124>]
(max8997_pmic_probe+0x5b8/0x69c)
> 
> Acked-by: MyungJoo Ham<myungjoo.ham@...sung.com>
Thanks.
> 
<snipped>

>> ---
>> drivers/regulator/max8997.c |    8 ++++----
>> 1 files changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/regulator/max8997.c b/drivers/regulator/max8997.c
>> index 10d5a1d..0fc7b8c 100644
>> --- a/drivers/regulator/max8997.c
>> +++ b/drivers/regulator/max8997.c
>> @@ -1124,6 +1124,10 @@ static __devinit int max8997_pmic_probe(struct platform_device *pdev)
>> 0x3f);
>> }
>>
>> + /* Misc Settings */
>> + max8997->ramp_delay = 10; /* set 10mV/us, which is the default */
>> + max8997_write_reg(i2c, MAX8997_REG_BUCKRAMP, (0xf<<  4) | 0x9);
>> +
>> for (i = 0; i<  pdata->num_regulators; i++) {
>> const struct voltage_map_desc *desc;
>> int id = pdata->regulators[i].id;
>> @@ -1148,10 +1152,6 @@ static __devinit int max8997_pmic_probe(struct platform_device *pdev)
>> }
>> }
>>
>> - /* Misc Settings */
>> - max8997->ramp_delay = 10; /* set 10mV/us, which is the default */
>> - max8997_write_reg(i2c, MAX8997_REG_BUCKRAMP, (0xf<<  4) | 0x9);
>> -
>> return 0;
>> err:
>> for (i = 0; i<  max8997->num_regulators; i++)
>> -- 
>> 1.7.4.1
>>
>>
> 
> 
> 
>   MyungJoo Ham (함명주)
> Mobile Software Platform Lab,
> Digital Media and Communications (DMC) Business
> Samsung Electronics
> cell: +82-10-6714-2858 / office: +82-31-279-8033


-- 
Tushar Behera
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