linux-kernel - Re: [PATCH v4 2/2] iio: vadc: Qualcomm SPMI PMIC voltage ADC driver

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Date:	Tue, 18 Nov 2014 10:23:33 +0200
From:	"Ivan T. Ivanov" <iivanov@...sol.com>
To:	Hartmut Knaack <knaack.h@....de>
Cc:	Jonathan Cameron <jic23@...nel.org>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>,
	Stanimir Varbanov <svarbanov@...sol.com>,
	Angelo Compagnucci <angelo.compagnucci@...il.com>,
	Grant Likely <grant.likely@...aro.org>,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org,
	devicetree@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v4 2/2] iio: vadc: Qualcomm SPMI PMIC voltage ADC driver


On Mon, 2014-11-17 at 23:12 +0100, Hartmut Knaack wrote:
> Ivan T. Ivanov schrieb am 12.11.2014 09:55:
> > On Tue, 2014-11-11 at 23:39 +0100, Hartmut Knaack wrote:
> > > Ivan T. Ivanov schrieb am 11.11.2014 09:21:
> > > > Hi Hartmut,
> > > > 
> > > > On Mon, 2014-11-10 at 22:11 +0100, Hartmut Knaack wrote:
> > > > > Ivan T. Ivanov schrieb am 03.11.2014 16:24:
> > > > > > From: Stanimir Varbanov <svarbanov@...sol.com>
> > > > > > 
> > > > > > The voltage ADC is peripheral of Qualcomm SPMI PMIC chips. It has
> > > > > > 15 bits resolution and register space inside PMIC accessible across
> > > > > > SPMI bus.
> > > > > > 
> > > > > > The vadc driver registers itself through IIO interface.
> > > > > Reviewing again, I got the feeling that due to the complexity of adc reads (writing to
> > > > > register
> > > > > to start conversion, waiting a decent time for the conversion to complete, reading the
> > > > > result),
> > > > > it would be beneficial to use a mutex in vadc_read_raw or its depending functions.
> > > > 
> > > > Hm, yes, but there is such a nice info_exist_lock :-) in core functions,
> > > > which in practice serve the same purpose.
> > > I seem to miss that. Please point me in the right direction.
> > 
> > I am referring to info_exist_lock mutex part of struct iio_dev.
> > It protects all operations inkern.c, no?
> > 
> Good point, thanks for helping me there.

I was wondering, is there a plan to improve this part of the code? 
I mean to remove per device lock and use something like try_module_get(),
when clients are acquiring reference to iio channel? 

> > > > > > +
> > > > > > +       ret = of_property_read_u32(node, "reg", &res);
> > > > > For u16, there would be of_property_read_u16().
> > > > > > +       if (ret < 0)
> > > > > > +       return -ENODEV;
> > > > > Just return ret here?
> > > > 
> > > > I am usually trying to follow these recommendations[1]. In practice driver
> > > > core cares only for EPROBE_DEFER, ENODEV and ENXIO, while of_property_read_u32()
> > > > can return ENODATA and EOVERFLOW, which did't not make sense for the core.
> > > Please point me in the right direction on this one, too. It is pretty common to pass error 
> > > codes
> > > up, as it is also mentioned in [1].
> > 
> > Yes, I know that is common to just pass error codes up, but in this case it did't
> > make too much sense, I think. Also take a look at realy_probe() and line 343.
> This doesn't convince me. Actually, within the probe_failed part, it just doesn't care about 
> ENODEV and ENXIO as long as debug messages are disabled (which apart from some developers, is 
> default for the vast majority of devices). For all other error codes, it will at least print an 
> info or warning about what's going wrong (and that can be a lot of help for debugging).

Well, if you insist... will change it.

Thanks, 
Ivan
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