Re: [PATCH v3 03/13] HID: core: fix unit exponent parsing

[Jiri Kosina]

On Wed, 7 Nov 2012, Benjamin Tissoires wrote:

> HID spec details special values for the HID field unit exponent.
> Basically, the range [0x8..0xf] correspond to [-8..-1], so this is
> a standard two's complement on a half-byte.
> 
> Signed-off-by: Benjamin Tissoires <benjamin.tissoires@xxxxxxxxx>

Acked-by: Jiri Kosina <jkosina@xxxxxxx>

> ---
>  drivers/hid/hid-core.c  | 16 +++++++++++++++-
>  drivers/hid/hid-input.c | 13 +++++++++----
>  include/linux/hid.h     |  1 +
>  3 files changed, 25 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/hid/hid-core.c b/drivers/hid/hid-core.c
> index 3d0da29..9da3007 100644
> --- a/drivers/hid/hid-core.c
> +++ b/drivers/hid/hid-core.c
> @@ -315,6 +315,7 @@ static s32 item_sdata(struct hid_item *item)
>  
>  static int hid_parser_global(struct hid_parser *parser, struct hid_item *item)
>  {
> +	__u32 raw_value;
>  	switch (item->tag) {
>  	case HID_GLOBAL_ITEM_TAG_PUSH:
>  
> @@ -365,7 +366,14 @@ static int hid_parser_global(struct hid_parser *parser, struct hid_item *item)
>  		return 0;
>  
>  	case HID_GLOBAL_ITEM_TAG_UNIT_EXPONENT:
> -		parser->global.unit_exponent = item_sdata(item);
> +		/* Units exponent negative numbers are given through a
> +		 * two's complement.
> +		 * See "6.2.2.7 Global Items" for more information. */
> +		raw_value = item_udata(item);
> +		if (!(raw_value & 0xfffffff0))
> +			parser->global.unit_exponent = hid_snto32(raw_value, 4);
> +		else
> +			parser->global.unit_exponent = raw_value;
>  		return 0;
>  
>  	case HID_GLOBAL_ITEM_TAG_UNIT:
> @@ -865,6 +873,12 @@ static s32 snto32(__u32 value, unsigned n)
>  	return value & (1 << (n - 1)) ? value | (-1 << n) : value;
>  }
>  
> +s32 hid_snto32(__u32 value, unsigned n)
> +{
> +	return snto32(value, n);
> +}
> +EXPORT_SYMBOL_GPL(hid_snto32);
> +
>  /*
>   * Convert a signed 32-bit integer to a signed n-bit integer.
>   */
> diff --git a/drivers/hid/hid-input.c b/drivers/hid/hid-input.c
> index 67044f3..7015080 100644
> --- a/drivers/hid/hid-input.c
> +++ b/drivers/hid/hid-input.c
> @@ -192,7 +192,6 @@ static int hidinput_setkeycode(struct input_dev *dev,
>  	return -EINVAL;
>  }
>  
> -
>  /**
>   * hidinput_calc_abs_res - calculate an absolute axis resolution
>   * @field: the HID report field to calculate resolution for
> @@ -235,17 +234,23 @@ __s32 hidinput_calc_abs_res(const struct hid_field *field, __u16 code)
>  	case ABS_MT_TOOL_Y:
>  	case ABS_MT_TOUCH_MAJOR:
>  	case ABS_MT_TOUCH_MINOR:
> -		if (field->unit == 0x11) {		/* If centimeters */
> +		if (field->unit & 0xffffff00)		/* Not a length */
> +			return 0;
> +		unit_exponent += hid_snto32(field->unit >> 4, 4) - 1;
> +		switch (field->unit & 0xf) {
> +		case 0x1:				/* If centimeters */
>  			/* Convert to millimeters */
>  			unit_exponent += 1;
> -		} else if (field->unit == 0x13) {	/* If inches */
> +			break;
> +		case 0x3:				/* If inches */
>  			/* Convert to millimeters */
>  			prev = physical_extents;
>  			physical_extents *= 254;
>  			if (physical_extents < prev)
>  				return 0;
>  			unit_exponent -= 1;
> -		} else {
> +			break;
> +		default:
>  			return 0;
>  		}
>  		break;
> diff --git a/include/linux/hid.h b/include/linux/hid.h
> index 9edb06c..a110a3e 100644
> --- a/include/linux/hid.h
> +++ b/include/linux/hid.h
> @@ -754,6 +754,7 @@ int hid_connect(struct hid_device *hid, unsigned int connect_mask);
>  void hid_disconnect(struct hid_device *hid);
>  const struct hid_device_id *hid_match_id(struct hid_device *hdev,
>  					 const struct hid_device_id *id);
> +s32 hid_snto32(__u32 value, unsigned n);
>  
>  /**
>   * hid_map_usage - map usage input bits
> -- 
> 1.7.11.7
> 

-- 
Jiri Kosina
SUSE Labs
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