Re: [PATCH 02/12] Input: synaptics - do not invert y if 0

[Chase Douglas <chase.douglas@canonical.com>]

On 06/28/2011 10:07 PM, djkurtz@chromium.org wrote:
> From: Daniel Kurtz <djkurtz@chromium.org>
> 
> Synaptics touchpads report increasing y from bottom to top.
> This is inverted from normal userspace "top of screen is 0" coordinates.
> Thus, the kernel driver reports inverted y coordinates to userspace.
> 
> In some cases, however, y = 0 is sent by the touchpad.
> In these cases, the kernel driver should not invert, and just report 0.

Under what cases is y sent as 0, and why do we want to report it as 0 to
userspace?

> 
> This patch also refactors the inversion into a macro, and moves it
> into packet processing instead of during position reporting.

It's getting really hard to read the bit transformations with a macro.
I'd prefer an approach that splits the computation. Maybe:

hw->y = bit_manipulations;
hw->y = INVERT_Y(hw->y);

(could use a temporary variable too)

Or maybe define a static inline function that takes the hw state as an arg:

hw->y = bit_manipulations;
fix_y(hw);

I'd prefer this implementation if every scenario involved manipulating
the y value of the hw state struct.

Also, it would be great if you could add your explanation of why Y is
inverted as a comment above INVERT_Y (or whatever function/macro it
eventually becomes).

Thanks!

-- Chase

> Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
> ---
>  drivers/input/mouse/synaptics.c |   16 +++++++++-------
>  1 files changed, 9 insertions(+), 7 deletions(-)
> 
> diff --git a/drivers/input/mouse/synaptics.c b/drivers/input/mouse/synaptics.c
> index e06e045..f6d0c04 100644
> --- a/drivers/input/mouse/synaptics.c
> +++ b/drivers/input/mouse/synaptics.c
> @@ -44,6 +44,8 @@
>  #define YMIN_NOMINAL 1408
>  #define YMAX_NOMINAL 4448
>  
> +#define INVERT_Y(y) (((y) != 0) ? (YMAX_NOMINAL + YMIN_NOMINAL - (y)) : 0)
> +
>  
>  /*****************************************************************************
>   *	Stuff we need even when we do not want native Synaptics support
> @@ -409,9 +411,9 @@ static int synaptics_parse_hw_state(const unsigned char buf[],
>  		hw->x = (((buf[3] & 0x10) << 8) |
>  			 ((buf[1] & 0x0f) << 8) |
>  			 buf[4]);
> -		hw->y = (((buf[3] & 0x20) << 7) |
> +		hw->y = INVERT_Y((((buf[3] & 0x20) << 7) |
>  			 ((buf[1] & 0xf0) << 4) |
> -			 buf[5]);
> +			 buf[5]));
>  
>  		hw->z = buf[2];
>  		hw->w = (((buf[0] & 0x30) >> 2) |
> @@ -421,7 +423,8 @@ static int synaptics_parse_hw_state(const unsigned char buf[],
>  		if (SYN_CAP_ADV_GESTURE(priv->ext_cap_0c) && hw->w == 2) {
>  			/* Gesture packet: (x, y, z) at half resolution */
>  			priv->mt.x = (((buf[4] & 0x0f) << 8) | buf[1]) << 1;
> -			priv->mt.y = (((buf[4] & 0xf0) << 4) | buf[2]) << 1;
> +			priv->mt.y = INVERT_Y((((buf[4] & 0xf0) << 4)
> +					      | buf[2]) << 1);
>  			priv->mt.z = ((buf[3] & 0x30) | (buf[5] & 0x0f)) << 1;
>  			return 1;
>  		}
> @@ -473,7 +476,7 @@ static int synaptics_parse_hw_state(const unsigned char buf[],
>  		}
>  	} else {
>  		hw->x = (((buf[1] & 0x1f) << 8) | buf[2]);
> -		hw->y = (((buf[4] & 0x1f) << 8) | buf[5]);
> +		hw->y = INVERT_Y(((buf[4] & 0x1f) << 8) | buf[5]);
>  
>  		hw->z = (((buf[0] & 0x30) << 2) | (buf[3] & 0x3F));
>  		hw->w = (((buf[1] & 0x80) >> 4) | ((buf[0] & 0x04) >> 1));
> @@ -491,8 +494,7 @@ static void set_slot(struct input_dev *dev, int slot, bool active, int x, int y)
>  	input_mt_report_slot_state(dev, MT_TOOL_FINGER, active);
>  	if (active) {
>  		input_report_abs(dev, ABS_MT_POSITION_X, x);
> -		input_report_abs(dev, ABS_MT_POSITION_Y,
> -				 YMAX_NOMINAL + YMIN_NOMINAL - y);
> +		input_report_abs(dev, ABS_MT_POSITION_Y, y);
>  	}
>  }
>  
> @@ -584,7 +586,7 @@ static void synaptics_process_packet(struct psmouse *psmouse)
>  
>  	if (num_fingers > 0) {
>  		input_report_abs(dev, ABS_X, hw.x);
> -		input_report_abs(dev, ABS_Y, YMAX_NOMINAL + YMIN_NOMINAL - hw.y);
> +		input_report_abs(dev, ABS_Y, hw.y);
>  	}
>  	input_report_abs(dev, ABS_PRESSURE, hw.z);
>