Re: [PATCH] iio: adc: vf610_adc: Fix division by zero error

[Jonathan Cameron]

On 26/10/15 16:21, Stefan Agner wrote:
> On 2015-10-25 05:20, Jonathan Cameron wrote:
>> On 19/10/15 08:43, Sanchayan Maity wrote:
>>> In case the fsl,adck-max-frequency property is not present in
>>> the device tree, a division by zero error results during the
>>> probe call on kernel boot (see below). This patch fixes it and
>>> also restores device tree compatibility in case kernels are
>>> booting with old device trees without this property specified.
>>>
>>> [    1.063229] Division by zero in kernel.
>>> [    1.067152] CPU: 0 PID: 1 Comm: swapper Not tainted
>>> 4.3.0-rc5-00212-gcc88cef #37
>>> [    1.074650] Hardware name: Freescale Vybrid VF5xx/VF6xx (Device Tree)
>>> [    1.081135] Backtrace:
>>> [    1.083694] [<800134a4>] (dump_backtrace) from [<8001369c>]
>>> (show_stack+0x18/0x1c)
>>> [    1.091340]  r7:00000008 r6:8e0ae210 r5:00000000 r4:8e299800
>>> [    1.097146] [<80013684>] (show_stack) from [<80297b1c>]
>>> (dump_stack+0x24/0x28)
>>> [    1.104483] [<80297af8>] (dump_stack) from [<80013608>]
>>> (__div0+0x1c/0x20)
>>> [    1.111421] [<800135ec>] (__div0) from [<802968b4>] (Ldiv0+0x8/0x10)
>>> [    1.117865] [<80424350>] (vf610_adc_probe) from [<803153b4>]
>>> (platform_drv_probe+0x4c/0xac)
>>> [    1.126311]  r10:00000000 r9:8076a5ec r8:00000000 r7:fffffdfb
>>> r6:807cc67c r5:8e0ae210
>>> [    1.134319]  r4:807f6c54
>>> [    1.136915] [<80315368>] (platform_drv_probe) from [<803138bc>]
>>> (driver_probe_device+0x20c/0x2f8)
>>> [    1.145882]  r7:807cc67c r6:00000000 r5:8e0ae210 r4:807f6c54
>>> [    1.151657] [<803136b0>] (driver_probe_device) from [<80313a3c>]
>>> (__driver_attach+0x94/0x98)
>>> [    1.160190]  r9:8076a5ec r8:00000098 r7:00000000 r6:8e0ae244
>>> r5:807cc67c r4:8e0ae210
>>> [    1.168112] [<803139a8>] (__driver_attach) from [<80311cb8>]
>>> (bus_for_each_dev+0x70/0xa4)
>>> [    1.176383]  r7:00000000 r6:803139a8 r5:807cc67c r4:00000000
>>> [    1.182159] [<80311c48>] (bus_for_each_dev) from [<80313318>]
>>> (driver_attach+0x24/0x28)
>>> [    1.190260]  r6:807bb568 r5:8e2a5b00 r4:807cc67c
>>> [    1.194996] [<803132f4>] (driver_attach) from [<80312f50>]
>>> (bus_add_driver+0x1a4/0x21c)
>>> [    1.203113] [<80312dac>] (bus_add_driver) from [<803142a8>]
>>> (driver_register+0x80/0x100)
>>> [    1.211275]  r7:8e2a7dc0 r6:807a8160 r5:80789e14 r4:807cc67c
>>> [    1.217075] [<80314228>] (driver_register) from [<803152f8>]
>>> (__platform_driver_register+0x5c/0x64)
>>> [    1.226216]  r5:80789e14 r4:807a8160
>>> [    1.229877] [<8031529c>] (__platform_driver_register) from
>>> [<80789e30>] (vf610_adc_driver_init+0x1c/0x20)
>>> [    1.239556] [<80789e14>] (vf610_adc_driver_init) from [<800095f8>]
>>> (do_one_initcall+0x94/0x1dc)
>>> [    1.248365] [<80009564>] (do_one_initcall) from [<8076ae34>]
>>> (kernel_init_freeable+0x13c/0x1e0)
>>> [    1.257155]  r10:80794830 r9:8076a5ec r8:00000098 r7:807d5780
>>> r6:807d5780 r5:00000006
>>> [    1.265153]  r4:807a0ee8
>>> [    1.267753] [<8076acf8>] (kernel_init_freeable) from [<80590ef0>]
>>> (kernel_init+0x18/0xf0)
>>> [    1.276021]  r10:00000000 r9:00000000 r8:00000000 r7:00000000
>>> r6:00000000 r5:80590ed8
>>> [    1.284015]  r4:807d5780
>>> [    1.286615] [<80590ed8>] (kernel_init) from [<8000f878>]
>>> (ret_from_fork+0x14/0x3c)
>>> [    1.294278]  r5:80590ed8 r4:00000000
>>>
>>> Signed-off-by: Sanchayan Maity <maitysanchayan@xxxxxxxxx>
>> I'd like an ack from Fugang on this as I'm less than entirely
>> sure what the current logic is doing!
> 
> I introduced adck_rate along wiht the fsl,adck-max-frequency device tree
> property to make sure the ADC operates within its specification. It is
> actually also necessary to (re-)calculate the proper adck_rate even when
> the fsl,adck-max-frequency property is set. Anyway, moving the
> calculation before the first use is the right thing to do. From my side:
> 
> Acked-by: Stefan Agner <stefan@xxxxxxxx>
> 
> A minor nit below:
> 
>>
>> Jonathan
>>> ---
>>>  drivers/iio/adc/vf610_adc.c | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/iio/adc/vf610_adc.c b/drivers/iio/adc/vf610_adc.c
>>> index 6bf4c20..bf4f3d8 100644
>>> --- a/drivers/iio/adc/vf610_adc.c
>>> +++ b/drivers/iio/adc/vf610_adc.c
>>> @@ -193,6 +193,8 @@ static inline void vf610_adc_calculate_rates(struct vf610_adc *info)
>>>  		adc_feature->clk_div = 8;
>>>  	}
>>>
>>> +	adck_rate = ipg_rate / info->adc_feature.clk_div;
>>> +
> 
> There is a local pointer variable to adc_feature, so this could look
> somewhat shorter:
> 
> adck_rate = ipg_rate / adc_feature->clk_div;
Fixed that up and applied to the fixes-togreg branch of iio.git
Marked for stable.

Thanks,

Jonathan
> 
> --
> Stefan
> 
>>>  	/*
>>>  	 * Determine the long sample time adder value to be used based
>>>  	 * on the default minimum sample time provided.
>>> @@ -217,7 +219,6 @@ static inline void vf610_adc_calculate_rates(struct vf610_adc *info)
>>>  	 * BCT (Base Conversion Time): fixed to 25 ADCK cycles for 12 bit mode
>>>  	 * LSTAdder(Long Sample Time): 3, 5, 7, 9, 13, 17, 21, 25 ADCK cycles
>>>  	 */
>>> -	adck_rate = ipg_rate / info->adc_feature.clk_div;
>>>  	for (i = 0; i < ARRAY_SIZE(vf610_hw_avgs); i++)
>>>  		info->sample_freq_avail[i] =
>>>  			adck_rate / (6 + vf610_hw_avgs[i] *
>>>

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