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SubjectRe: [PATCH 1/2] iio: adc: ti_am335x_adc: Protect FIFO1 from concurrent access
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On Tuesday 09 August 2016 03:21 PM, Matt Ranostay wrote:
> On Mon, Aug 8, 2016 at 4:05 AM, Vignesh R <vigneshr@ti.com> wrote:
>> It is possible that two or more ADC channels can be simultaneously
>> requested for raw samples, in which case there can be race in access to
>> FIFO data resulting in loss of samples.
>> If am335x_tsc_se_set_once() is called again from tiadc_read_raw(), when
>> ADC is still acquired to sample one of the channels, the second process
>> might be put into uninterruptible sleep state. Fix these issues, by
>> protecting FIFO access and channel configurations with a mutex. Since
>> tiadc_read_raw() might take anywhere between few microseconds to few
>> milliseconds to finish execution (depending on averaging and delay
>> values supplied via DT), its better to use mutex instead of spinlock.
>>
>> Signed-off-by: Vignesh R <vigneshr@ti.com>
>> ---
>> drivers/iio/adc/ti_am335x_adc.c | 14 +++++++++++---
>> 1 file changed, 11 insertions(+), 3 deletions(-)
>>
>> diff --git a/drivers/iio/adc/ti_am335x_adc.c b/drivers/iio/adc/ti_am335x_adc.c
>> index 8a368756881b..bed9977a1863 100644
>> --- a/drivers/iio/adc/ti_am335x_adc.c
>> +++ b/drivers/iio/adc/ti_am335x_adc.c
>> @@ -32,6 +32,7 @@
>>
>> struct tiadc_device {
>> struct ti_tscadc_dev *mfd_tscadc;
>> + struct mutex fifo1_lock; /* to protect fifo access */
>
> Are there more than one FIFOs, or even possible? Just wondering the
> number indexing here..

ADC IP as such as two FIFOs: FIFO0 and FIFO1. FIFO0 is dedicated for
touchscreen channels and FIFO1 is used for ADC channels. Its not
possible to use FIFO0 for ADC, but to match h/w register naming, I used
above name for mutex.

--
Regards
Vignesh

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