linux-kernel - Re: [PATCH v6] iio: adc: add new lp8788 adc driver

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Date:	Tue, 18 Sep 2012 21:18:25 +0100
From:	Jonathan Cameron <jic23@...nel.org>
To:	Lars-Peter Clausen <lars@...afoo.de>
CC:	"Kim, Milo" <Milo.Kim@...com>, Jonathan Cameron <jic23@....ac.uk>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v6] iio: adc: add new lp8788 adc driver

On 09/18/2012 09:19 AM, Lars-Peter Clausen wrote:
> On 09/17/2012 11:35 AM, Kim, Milo wrote:
>>  TI LP8788 PMU provides regulators, battery charger, ADC,
>>  RTC, backlight driver and current sinks.
>>
>>  This patch enables the LP8788 ADC functions.
>>
>>  The LP8788 ADC has several ADC input selection and supports 12bit resolution.
>>  Internal operation of getting ADC is access to registers of LP8788.
>>  The LP8788 ADC uses exported functions for accessing these registers.
>>  (exported by LP8788 MFD device driver)
>>
>>  This driver supports IIO_CHAN_INFO_RAW and SCALE.
>>  So the IIO consumer can calculate the value with raw and scale.
>>  The unit of scale is micro.
>>
>>  (ADC Input Selection)
>>
>>  Voltage: battery voltage (MAX 5.0, 5.5 and 6.0V)
>>           charger input voltage
>>           four general ADC inputs
>>           coin cell voltage
>>  Current: battery charging current
>>  Temperature: IC temperature
>>
>>  (The IIO map for the IIO consumer)
>>
>>  The ADC input is configurable in the platform side.
>>  Even though this platform data is not defined,
>>  the default IIO map is created for supporting the power supply driver.
>>  The battery voltage and temperature are used inside this driver.
>>
>>  (History)
>>
>>  Patch v6.
>>  (a) Fix scale value for each ADC input selection
>>  Voltage and current type are mili unit and temperature is degree.
>>  To calculate the IC temperature,
>>  temp = raw * scaleint + (raw * scalepart)/ 1000000, scaleint is always 0.
>>       = raw * 0.061050, raw: 0 ~ 4095
>>  Then range of IC temperature(ADC result) is 0 ~ 250'C
>>
>>  (b) Reorganization of the IIO channel Spec
>>  Remove address, scan_type and scan_index and rollback the datasheet name.
>>  The reason why 'address' field is unnecessary is no relation with each channel.
>>  Moreover, to get the raw ADC value, the address info is not only one register
>>  but also several registers.
>>  Therefore specific function(lp8788_get_adc_result) is called rather than
>>  using one 'address' field.
>>
>>  (c) Fix coding style
>>  Remove duplicated checking routine while unregistering the IIO map.
>>  Fix code for space and parenthesis.
>>
>>  Patch v5.
>>  Fix default consumer name as 'lp8788-charger'.
>>  Add mutex for ADC read operation.
>>  Reorganization on lp8788_adc_read_raw().
>>
>>  Patch v4.
>>  Fix adc_raw function: support RAW and SCALE channel info.
>>  Change LP8788 ADC platform data - iio map.
>>  Enables the default IIO map.
>>
>>  Patch v3.
>>  Fix wrong size of allocating iio private data.
>>  Fix coding styles.
>>
>>  Patch v2.
>>  Support RAW and SCALE interface for IIO consumer.
>>  Clean up the iio channel spec macro.
>>
>> Signed-off-by: Milo(Woogyom) Kim <milo.kim@...com>
> 
> Looks good to me,
> 
> Reviewed-by: Lars-Peter Clausen <lars@...afoo.de>
I've added this to my local tree but not pushed out just
yet on basis you might want to change the behaviour Lars
has pointed out...

I don't here it'll go as is in a day or so.

Jonathan
> 
> One comment though, not sure if it is critical or not.
> 
>> +static int lp8788_get_adc_result(struct lp8788_adc *adc, enum lp8788_adc_id id,
>> +				int *val)
>> +{
>> +	unsigned int msb;
>> +	unsigned int lsb;
>> +	unsigned int result;
>> +	u8 data;
>> +	u8 rawdata[2];
>> +	int size = ARRAY_SIZE(rawdata);
>> +	int retry = 5;
>> +	int ret;
>> +
>> +	data = (id << 1) | ADC_CONV_START;
>> +	ret = lp8788_write_byte(adc->lp, LP8788_ADC_CONF, data);
>> +	if (ret)
>> +		goto err_io;
>> +
>> +	/* retry until adc conversion is done */
>> +	data = 0;
>> +	while (retry--) {
>> +		usleep_range(100, 200);
>> +
>> +		ret = lp8788_read_byte(adc->lp, LP8788_ADC_DONE, &data);
>> +		if (ret)
>> +			goto err_io;
>> +
>> +		/* conversion done */
>> +		if (data)
>> +			break;
> 
> Could as well go into the while header like this:
>     while (!data && retry--)
> 
>> +	}
>> +
> 
> You still sample the data, even if there was a timeout and ADC_DONE is not set.
> 
>> +	ret = lp8788_read_multi_bytes(adc->lp, LP8788_ADC_RAW, rawdata, size);
>> +	if (ret)
>> +		goto err_io;
>> +
>> +	msb = (rawdata[0] << 4) & 0x00000ff0;
>> +	lsb = (rawdata[1] >> 4) & 0x0000000f;
>> +	result = msb | lsb;
>> +	*val = result;
>> +
>> +	return 0;
>> +
>> +err_io:
>> +	return ret;
>> +}
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