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

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Date:	Wed, 11 Feb 2009 00:51:25 +0100
From:	Giuseppe Bilotta <giuseppe.bilotta@...il.com>
To:	Éric Piel <Eric.Piel@...mplin-utc.net>
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

On Wed, Feb 11, 2009 at 12:46 AM, Éric Piel <Eric.Piel@...mplin-utc.net> wrote:
> 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 :-)

And don't forget about the v3 for -mm ;-)

> 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?

Well, the previous one works, but I admit it's horribly convoluted.
I'll double check with this one and resubmit (I'll only resubmit the
one based on Pavel's "don't touch anything on init" probably though,
hope it's ok)


-- 
Giuseppe "Oblomov" Bilotta
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