Re: lis302 DT binding for Nokia N900

[Sebastian Reichel <sre-8fiUuRrzOP0dnm+yROfE0A@public.gmane.org>]

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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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