linux-kernel - Re: [PATCH] iio: Add IIO support for the DAC on the Apex Embedded Systems STX104

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Message-ID: <20160208133507.GA13554@sophia>
Date:	Mon, 8 Feb 2016 08:35:07 -0500
From:	William Breathitt Gray <vilhelm.gray@...il.com>
To:	Jonathan Cameron <jic23@...nel.org>
Cc:	knaack.h@....de, lars@...afoo.de, pmeerw@...erw.net,
	linux-iio@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] iio: Add IIO support for the DAC on the Apex Embedded
 Systems STX104

On Sat, Feb 06, 2016 at 07:15:41PM +0000, Jonathan Cameron wrote:
>On 02/02/16 23:30, William Breathitt Gray wrote:
>> The Apex Embedded Systems STX104 is a 16-channel 16-bit analog input and
>> 2-channel 16-bit analog output PC/104 card. The STX104 incorporates a
>> large one mega-sample FIFO.
>> 
>> This driver provides IIO support for the 2-channel DAC on the STX104.
>> The base port address for the device may be configured via the
>> stx104_base module parameter.
>Nice looking product.
>> 
>> Signed-off-by: William Breathitt Gray <vilhelm.gray@...il.com>
>I'm a little out of my depth wrt to the lack of discoverability of
>this so perhaps take comments related to that rather more loosely
>than the IIO stuff.

Unfortunately, the Apex Embedded Systems STX104 lacks hardware
discoverability functionality; users are expected to manually set the
base address of the card via physical jumpers, then point their software
to match the set base address of the card.

>Again, module parameter usage will restrict you to instantiating only
>one instance.  Strikes me as a device where you might want more than one.
>Does the hardware prevent this for some reason?

That is a good point; I overlooked the fact that my current
implementation restricts the module to only one instance. Since PC/104
cards are effectively ISA cards, instead of the platform driver I will
reimplement the module to use the ISA bus driver provided in the
linux/isa.h file. I will also allow users to pass in a list of base
addresses in order to support multiple instances.

>> +#define STX104_CHAN(chan) {				\
>> +	.type = IIO_VOLTAGE,				\
>> +	.channel = chan,				\
>> +	.info_mask_separate = BIT(IIO_CHAN_INFO_RAW),	\
>No information available on scale?

I'm relatively new to the IIO subsystem, so let me know if I
misunderstood: the scale member allows users to view what output range
the device is set to use. The Apex Embedded Systems STX104 may be set to
one of four output voltage range modes: +-10V, +-5V, 0-10V, and 0-5V.
Unfortunately, these modes are configured via physical jumpers on the
card -- and because the card provides no hardware functionality to probe
for its configuration, the scale member should not be set since any
value would be at best a guess.

>> +	const char *const name = dev_name(dev);
>Personally I'd not bother with the local name variable but just use
>dev_name(dev) inline.

I'll incorporate this change in version 2 of this patch. 

>> +static int stx104_remove(struct platform_device *pdev)
>> +{
>> +	struct iio_dev *indio_dev = platform_get_drvdata(pdev);
>> +
>> +	iio_device_unregister(indio_dev);
>If there really is nothing to be done other than unregister, then
>use devm_iio_device_register(...) and you can drop the remove entirely.

Thanks, I wasn't aware of the devm_iio_device_register call! I'll
incorporate this change in version 2 of this patch. 

William Breathitt Gray