lis302 DT binding for Nokia N900

lis302 DT binding for Nokia N900

[Sebastian Reichel]

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Hi,

The lis302 has already a DT binding described in [0],
which descibes misc. hardware properties. The problem
is, that the Nokia N900 needs negative values for some
of the properties, which seem to be unsupported by DT.
The following values would be needed for the N900 (taken
from board code):

st,axis-x = <1>;  /* LIS3_DEV_X */
st,axis-y = <-2>; /* LIS3_INV_DEV_Y */
st,axis-z = <-3>; /* LIS3_INV_DEV_Z */

st,min-limit-x = <-32>;
st,min-limit-y = <3>;
st,min-limit-z = <3>;

st,max-limit-x = <-3>;
st,max-limit-y = <32>;
st,max-limit-z = <32>;

Can you please tell me how to setup the properties correctly?

[0] Documentation/devicetree/bindings/misc/lis302.txt

-- Sebastian

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Re: lis302 DT binding for Nokia N900

[Éric Piel]

On 03-12-13 13:21, Sebastian Reichel wrote:
> Hi,
>
> The lis302 has already a DT binding described in [0],
> which descibes misc. hardware properties. The problem
> is, that the Nokia N900 needs negative values for some
> of the properties, which seem to be unsupported by DT.
> The following values would be needed for the N900 (taken
> from board code):
>
> st,axis-x = <1>;  /* LIS3_DEV_X */
> st,axis-y = <-2>; /* LIS3_INV_DEV_Y */
> st,axis-z = <-3>; /* LIS3_INV_DEV_Z */
>
> st,min-limit-x = <-32>;
> st,min-limit-y = <3>;
> st,min-limit-z = <3>;
>
> st,max-limit-x = <-3>;
> st,max-limit-y = <32>;
> st,max-limit-z = <32>;
>
> Can you please tell me how to setup the properties correctly?

Hi Sebastian,
The code to support inversion of the axis is there... but apparently 
only in the I2C code. It seems the SPI code doesn't (yet) use any of 
these values. Is the accelerometer on the N900 connected via SPI, by 
chance?

It should be pretty simple to extend the SPI driver to support axis 
conversion too. It'd basically be a copy-paste of lis3lv02d_i2c_probe()

Concerning {min,max}-limit-*, I only have vague understanding of this 
information (only used in self test), but it should already be working 
fine with both I2C and SPI (as it's bus independent). In addition, note 
that it's compared to raw data (i.e., before axis conversion), so you 
probably don't need to put negative values there.

Éric
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Re: lis302 DT binding for Nokia N900

[Sebastian Reichel]

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Hi Éric,

On Sun, Dec 08, 2013 at 02:27:52PM +0100, Éric Piel wrote:
> On 03-12-13 13:21, Sebastian Reichel wrote:
> >The lis302 has already a DT binding described in [0],
> >which descibes misc. hardware properties. The problem
> >is, that the Nokia N900 needs negative values for some
> >of the properties, which seem to be unsupported by DT.
> >The following values would be needed for the N900 (taken
> >from board code):
> >
> >st,axis-x = <1>;  /* LIS3_DEV_X */
> >st,axis-y = <-2>; /* LIS3_INV_DEV_Y */
> >st,axis-z = <-3>; /* LIS3_INV_DEV_Z */
> >
> >st,min-limit-x = <-32>;
> >st,min-limit-y = <3>;
> >st,min-limit-z = <3>;
> >
> >st,max-limit-x = <-3>;
> >st,max-limit-y = <32>;
> >st,max-limit-z = <32>;
> >
> >Can you please tell me how to setup the properties correctly?
> 
> The code to support inversion of the axis is there... but apparently
> only in the I2C code. It seems the SPI code doesn't (yet) use any of
> these values. Is the accelerometer on the N900 connected via SPI, by
> chance?

No, it's connected via I2C. Please note, that the N900's accelerometer
is already supported, but only when initialized via legacy boardcode.

The problem is, that I can't specify negative values in the device
tree file (the device tree compiler complains). I couldn't find any
example of negative numbers in any dts file, so I guess, that
negative numbers are not supported.

> It should be pretty simple to extend the SPI driver to support axis
> conversion too. It'd basically be a copy-paste of
> lis3lv02d_i2c_probe()
> 
> Concerning {min,max}-limit-*, I only have vague understanding of
> this information (only used in self test), but it should already be
> working fine with both I2C and SPI (as it's bus independent). In
> addition, note that it's compared to raw data (i.e., before axis
> conversion), so you probably don't need to put negative values
> there.

I just want to port the existing boardcode to device tree.
The existing platform data is defined as rx51_lis3lv02d_data in
arch/arm/mach-omap2/board-rx51-peripherals.c.

-- Sebastian

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Re: lis302 DT binding for Nokia N900

[Éric Piel]

On 08-12-13 14:46, Sebastian Reichel wrote:
:
> No, it's connected via I2C. Please note, that the N900's accelerometer
> is already supported, but only when initialized via legacy boardcode.
>
> The problem is, that I can't specify negative values in the device
> tree file (the device tree compiler complains). I couldn't find any
> example of negative numbers in any dts file, so I guess, that
> negative numbers are not supported.
>
:
> I just want to port the existing boardcode to device tree.
> The existing platform data is defined as rx51_lis3lv02d_data in
> arch/arm/mach-omap2/board-rx51-peripherals.c.
Oh! Yes, then the values themselves should be fine.
Indeed, the problem is in the parsing of the DT values.
Currently, lis3lv02d_init_dt() reads values as unsigned int:

u32 val;
if (of_get_property(np, "st,axis-x", &val))
	pdata->axis_x = val;

So it's quite unlikely to get negative ;-) Is there a way to read signed 
ints in DT? If so, I can update the driver.

Éric
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Re: lis302 DT binding for Nokia N900

[Sebastian Reichel]

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On Sun, Dec 08, 2013 at 03:00:36PM +0100, Éric Piel wrote:
> On 08-12-13 14:46, Sebastian Reichel wrote:
> :
> >No, it's connected via I2C. Please note, that the N900's accelerometer
> >is already supported, but only when initialized via legacy boardcode.
> >
> >The problem is, that I can't specify negative values in the device
> >tree file (the device tree compiler complains). I couldn't find any
> >example of negative numbers in any dts file, so I guess, that
> >negative numbers are not supported.
> >
> :
> >I just want to port the existing boardcode to device tree.
> >The existing platform data is defined as rx51_lis3lv02d_data in
> >arch/arm/mach-omap2/board-rx51-peripherals.c.
> Oh! Yes, then the values themselves should be fine.
> Indeed, the problem is in the parsing of the DT values.
> Currently, lis3lv02d_init_dt() reads values as unsigned int:
> 
> u32 val;
> if (of_get_property(np, "st,axis-x", &val))
> 	pdata->axis_x = val;
> 
> So it's quite unlikely to get negative ;-) Is there a way to read
> signed ints in DT? If so, I can update the driver.

I just found a link, which describes how to put negative values into
the DTS, so that the device tree compiler understands them and
translates them into 2's-compliment [0].

The kernel code currently does not provide of_property_read_s32(),
but it seems that there was just no use case so far. At least one
of the DT binding maintainers seems to be finde with introducing it
[1].

I will prepare a patch, which adds of_property_read_s32 and another
one, which updates lis3lv02d to use the new function.

[0] http://www.mail-archive.com/linux-arm-msm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org/msg05121.html
[1] http://www.mail-archive.com/linux-arm-msm-u79uwXL29TY76Z2rM5mHXA@public.gmane.org/msg05125.html

-- Sebastian

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