Enable some auto-centering by default?

[chrisboyle]

Just not the hard autocenter that was there before these patches.

@Fred41 points out that the Windows driver sends 0x00 0x21 0x7f 0x46 (for _padding0, autocenter_strength, autocenter_force, autocenter_damping respectively) and writes:

I agree, it should be:

1. initialised at device connect
2. light and unobstrusive, minimal deadband (max coefficient, low saturation)
3. disabled/overwritten, as soon as an ff-client starts a condition effect
4. restored, if client disconnects

Maybe i should add: i think it can't be wrong to use a dedicated (8 resp. 4 byte) spring and/or damper condition slot for this purpose, because this slots can be reused if a ff-client connects.

... some weeks later:

I tested your linux driver against 5.2-rc2, your patch(es) works still great.

After some ffb related firmware research, i found the following implementation details confirmed:

• there are really 2 slots for dedicated spring and damper effects (two dimensions each)
• there is one combined (spring,damper and combined saturation, two dimensions) effect for hand on stick
• there is one combined (spring,damper and combined saturation, two dimensions) effect for hand off, only as parameter set in firmware

Here is a link to my latest firmware patch:
https://github.com/fred41/G940-firmware-fixes

So my final view of the struct is something like this:

typedef` struct {
	int16_t	constant_force;
	int8_t	pad0;
	int8_t	combined_spring_coeff;
	int8_t	combined_spring_saturation;
	int8_t	combined_damper_coeff;
	int16_t	spring0_deadzone_neg;
	int16_t	spring0_deadzone_pos;
	int8_t	spring0_coeff_neg;
	int8_t	spring0_coeff_pos;
	int16_t	spring0_saturation;
	int16_t	spring1_deadzone_neg;
	int16_t	spring1_deadzone_pos;
	int8_t	spring1_coeff_neg;
	int8_t	spring1_coeff_pos;
	int16_t	spring1_saturation;
	int8_t	damper0_coeff_neg;
	int8_t	damper0_coeff_pos;
	int16_t	damper0_saturation;
	int8_t	damper1_coeff_neg;
	int8_t	damper1_coeff_pos;
	int16_t	damper1_saturation;
} __attribute__((packed, aligned(1))) ff_axis_t;

typedef struct {
	ff_axis_t x;
	ff_axis_t y;
} __attribute__((packed, aligned(1))) ff_t;