linux-kernel - Re: [PATCH] iio: acpi: Add ACPI0008 Ambient Light Sensor

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Date:	Thu, 30 Apr 2015 13:27:43 +0200
From:	Gabriele Mazzotta <gabriele.mzt@...il.com>
To:	Marek Vasut <marex@...x.de>
Cc:	jic23@...nel.org, knaack.h@....de, lars@...afoo.de,
	pmeerw@...erw.net, marxin.liska@...il.com, rui.zhang@...el.com,
	linux-kernel@...r.kernel.org, linux-iio@...r.kernel.org
Subject: Re: [PATCH] iio: acpi: Add ACPI0008 Ambient Light Sensor

On Thursday 30 April 2015 11:44:36 Marek Vasut wrote:
> On Wednesday, April 29, 2015 at 05:36:32 PM, Gabriele Mazzotta wrote:
> [...]
> > > > I'm sorry, I've just noticed that I haven't changed the value of
> > > > realbits in acpi_als_channels. This makes me wonder what would be the
> > > > proper value, given that this is a generic driver and all the
> > > > information I have are those in the ACPI specification (which states
> > > > what I reported here above).
> > > > 
> > > > Should I just set realbits to 32?
> > > 
> > > I believe the ALS reports only 16bit signel value, no ?
> > > My observation with a strong coherent light source is that
> > > the saturated sensor reported 0xffff .
> > 
> > Probably it's the same for me. I couldn't get to the point where
> > ALI reports 0xffff, just really close, I will have to try with some
> > stronger lights. However, looking at my ACPI table, I can see that
> > the value returned by _ALI is just the composition of two 8 bits
> > variables put side by side, so yes, I can say that even on my system
> > it's a 16bit value.
> 
> What kind of hardware are you testing this on ?

Dell XPS13 9333.

> > The problem here is that I'm not sure we can assume this as true in
> > general since the ACPI specification doesn't say anything.
> 
> Maybe someone more knowledgable can speak up.

I'm looking at some documentation from Microsoft [1] on how to use these
sensors in Windows and values as high as 100,000 lux are mentioned.

[1] https://msdn.microsoft.com/en-us/library/windows/hardware/dn613948%28v=vs.85%29.aspx

> Best regards,
> Marek Vasut

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