linux-kernel - Re: [PATCHv2] lis3lv02d: support both one- and two-byte sensors

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Date:	Wed, 11 Feb 2009 00:46:24 +0100
From:	Éric Piel <Eric.Piel@...mplin-utc.net>
To:	Giuseppe Bilotta <giuseppe.bilotta@...il.com>
Cc:	git@...r.kernel.org, Pavel Machek <pavel@...e.cz>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCHv2] lis3lv02d: support both one- and two-byte sensors

Giuseppe Bilotta schreef:
> Sensors responding with 0x3B to WHO_AM_I only have one data register per
> direction, thus returning a signed byte from the position which is
> occupied by the MSB in sensors responding with 0x3A.
> 
> We support both kind of sensors by checking for the sensor type on init
> and defining appropriate data-access routines and sensor limits (for the
> joystick) depending on what we find.
> 
> Signed-off-by: Giuseppe Bilotta <giuseppe.bilotta@...il.com>
> ---
> 
> This is the other version of the patch, and it changes access to use the
> base address from the 8-bit, so the 16-bit routine is changed to access
> the PREVIOUS byte for the LSB.
> 
> Choose whichever of the patches is deemed more correct 8-)
> 
> Note that both patches are based off Linus tree, so I don't know how
> they cope with Pavel's "don't touch too much on init" one. I'll try to
> work out a patch on top of that too.
Yes, great, and this one looks even better than v1 :-)
However I'm not sure about the conversion between s8 and s16:

> +static s16 lis3lv02d_read_8(acpi_handle handle, int reg)
> +{
> +	u8 lo;
> +	adev.read(handle, reg, &lo);
> +	return *((s8*)(&lo));
> +}
Does it really extend the sign to 16 bits? I would have written it this way:
+static s16 lis3lv02d_read_8(acpi_handle handle, int reg)
+{
+	s8 lo;
+	adev.read(handle, reg, &lo);
+	return (s16)lo;
+}
Doesn't it work better?

Eric
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