linux-kernel - Re: [RFC] [PATCH] digital compass hmc5843

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Message-ID: <4C2DDD2B.5090401@jic23.retrosnub.co.uk>
Date:	Fri, 02 Jul 2010 13:35:55 +0100
From:	Jonathan Cameron <kernel@...23.retrosnub.co.uk>
To:	"Datta, Shubhrajyoti" <shubhrajyoti@...com>
CC:	Jonathan Cameron <jic23@....ac.uk>,
	"linux-iio@...r.kernel.org" <linux-iio@...r.kernel.org>,
	"sfking@...dc.com" <sfking@...dc.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH] digital compass hmc5843

On 07/02/10 11:53, Datta, Shubhrajyoti wrote:
>>
>> <snip>
>>>
>>> I think that having a Hz as units will have its own issues. First the
>> decimal implementation. However I am open to the implementation.
>>> Also do you know of a driver that takes care of this.
>> None of the current drivers go below 1Hz so not quite the same.
>> lis3l02dq (accelerometer) does the match against a list, but it
>> is done numerically rather than via string matches as would be needed
>> here.
>>>
>>>>
>>>> static IIO_CONST_ATTR_SAMP_FREQ_AVAIL("0.5 1 2 5 10 20 50");
>>>>
>>>>
>>>> Then strncmp with the options to set the value up.  The rounding
>> approach
>>>> gets tricky with a non integer value so probably easier to only allow
>>>> these
>>>> values.
> 
> What is a recommended way of getting a double or float
> Is there any Strict_srttod etc.
> 
You can't, hence the suggestion of comparing strings not numerical values.

>>>
>>> Allowing only this value will result in default/ reject case and will
>> keep the previous value, may confuse the application
>> Then the application is ignoring the interface spec that says it must read
>> _available files if they are there.
>> This way the rounding behaviour is left to userspace and what the
>> application prefers rather
>> than in kernel actually making it the most flexible option.
> 
> Agree 
>>>
>>>>
>>>>> +static IIO_DEV_ATTR_AVAIL_SAMP_FREQ(show_avail_samp_freq);
>>>>> +
>>>>> +static s32 hmc5843_set_rate(struct i2c_client *client,
>>>>> +                               u8 rate)
>>>>> +{
>>>>> +       struct hmc5843_data *data = i2c_get_clientdata(client);
>>>>> +       u8 reg_val;
>>>>> +
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