linux-kernel - Re: [PATCH resent] lis3: Add axes module parameter for custom axis-mapping

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Date:	Thu, 23 Sep 2010 12:23:08 -0700
From:	Andrew Morton <akpm@...ux-foundation.org>
To:	Takashi Iwai <tiwai@...e.de>
Cc:	Éric Piel <Eric.Piel@...mplin-utc.net>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH resent] lis3: Add axes module parameter for custom
 axis-mapping

On Wed, 22 Sep 2010 13:31:19 +0200
Takashi Iwai <tiwai@...e.de> wrote:

> The axis-mapping of lis3dev device on many (rather most) HP machines
> doesn't follow the standard.  When each new model appears, users need
> to adjust again.  Testing this requires the rebuild of kernel, thus
> it's not trivial for end-users.
> 
> This patch adds a module parameter "axes" to allow a custom
> axis-mapping without patching and recompiling the kernel driver.
> User can pass the parameter such as axes=3,2,1.  Also it can be
> changed via sysfs.

Is the sysfs interface documented anywhere?

> --- a/drivers/hwmon/hp_accel.c
> +++ b/drivers/hwmon/hp_accel.c
> @@ -146,7 +146,8 @@ int lis3lv02d_acpi_write(struct lis3lv02d *lis3, int reg, u8 val)
>  
>  static int lis3lv02d_dmi_matched(const struct dmi_system_id *dmi)
>  {
> -	lis3_dev.ac = *((struct axis_conversion *)dmi->driver_data);
> +	memcpy(lis3_dev.axis_map, (int *)dmi->driver_data,
> +	       sizeof(lis3_dev.axis_map));

It's unobvious why the (nice) three-member struct was converted to a
(nasty) three-element array?  All those typesafe struct assignments
were turned into non-typesafe memcpys?

> +module_param_array_named(axes, lis3_dev.axis_map, axis, NULL, 0644);

Just to support module_param_array_named()?  If so, could have used a
union?

union axis_conversion {	/* should be called lis3_axis_conversion! */
	struct {
		int x;
		int y;
		int z;
	};
	int as_array[3];
};

or use a tyecast in the module_param_array_named() statement, perhaps?
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