linux-kernel - Re: iio/hid-sensor-accel-3d: no output from /dev/iio:device*?

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Date:	Thu, 17 Dec 2015 17:07:03 -0800
From:	Nish Aravamudan <nish.aravamudan@...il.com>
To:	Srinivas Pandruvada <srinivas.pandruvada@...ux.intel.com>
Cc:	Jiri Kosina <jikos@...nel.org>,
	Jonathan Cameron <jic23@...nel.org>,
	Hartmut Knaack <knaack.h@....de>,
	Lars-Peter Clausen <lars@...afoo.de>,
	Peter Meerwald <pmeerw@...erw.net>,
	linux-input@...r.kernel.org, linux-iio@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Crt Mori <cmo@...exis.com>
Subject: Re: iio/hid-sensor-accel-3d: no output from /dev/iio:device*?

On Thu, Dec 17, 2015 at 4:51 PM, Srinivas Pandruvada
<srinivas.pandruvada@...ux.intel.com> wrote:
> On Thu, 2015-12-17 at 15:38 -0800, Nish Aravamudan wrote:
>> [Starting a new thread from https://lkml.org/lkml/2015/12/15/663, as
>> now my laptop is displaying values in the sysfs *raw* files.]
>>
>> So I'm trying to understand exactly how the hid-sensor-accel-3d
>> driver works.
>>
>> If I turn up debugging, when I `cat
>> /sys/bus/iio/devices/device*/*raw*`, I see "iio iio:device3:
>> accel_3d_proc_event" and I think that means that
>> hid_sensor_push_data() is getting called.
>>
>> But read()'s on /dev/iio:device3 never produces anything, which is
>> what iio-sensor-proxy uses to translate events to dbus.
>>
>> Is it expected that the dev-node is "silent"? Just trying to
>> understand if an extension to the driver to support a chardev based
>> output is appropriate, or if iio-sensor-proxy needs to be changed to
>> handle this device.
>
> You are saying there is some regression. This used to work and now it
> doesn't work. Is raw values are displayed correctly, when you do "cat"?
> If cat of raw values is working then power on of sensors is working.

Sorry, I was unclear. I don't know if this is a regression. I can try
going back to an older kernel to see if the /dev/iio:device* files
produced any output.

Yes, the *raw* files in sysfs are producing output, that is changing
as I move the laptop around. But the /dev/ nodes seem to produce no
output (I'm still reading through the driver code to understand where
that data should be coming from.

> Turn on HID debug prints. If it is regression we can do git bisect.
> Any ACPI or PM changes can break this. Usually there will be GPIOs
> which will be involved in power on, where ACPI comes into play. This
> will be done by i2c-hid. There are some prints in i2c-hid which can be
> enabled also.

Ok, I will try this, as well.

-Nish
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