[ CCing Gary Stein ]
On Mon, 11 Mar 2019, Chris Boyle wrote:
> Disable default auto-centering of the Logitech G940, which otherwise
> makes the stick difficult to use. Also when autocenter is requested, obey
> the magnitude.
>
> The auto-centering effect will only unlock (or become the requested
> level) when an application starts using the joystick and the hand sensor
> on the stick is covered. That appears to be a hardware limitation.
>
> To make the above and future work on spring/damper support simpler and
> more type-safe, add a struct of the HID report. Many thanks to fred41 from
> forums.x-plane.org for useful information towards that.
>
> It seems byte 0 does not need to be a "command byte" of 0x51; it can be
> anything and is the least-significant byte of the constant force.
>
> Signed-off-by: Chris Boyle <chris@xxxxxxxxxx>
> ---
> drivers/hid/hid-lg3ff.c | 148 +++++++++++++++++++++-------------------
> 1 file changed, 78 insertions(+), 70 deletions(-)
>
> diff --git a/drivers/hid/hid-lg3ff.c b/drivers/hid/hid-lg3ff.c
> index 8c2da183d3bc..6fcd449d5b46 100644
> --- a/drivers/hid/hid-lg3ff.c
> +++ b/drivers/hid/hid-lg3ff.c
> @@ -2,6 +2,7 @@
> * Force feedback support for Logitech Flight System G940
> *
> * Copyright (c) 2009 Gary Stein <LordCnidarian@xxxxxxxxx>
> + * Copyright (c) 2019 Chris Boyle
> */
>
> /*
> @@ -26,51 +27,68 @@
>
> #include "hid-lg.h"
>
> -/*
> - * G940 Theory of Operation (from experimentation)
> - *
> - * There are 63 fields (only 3 of them currently used)
> - * 0 - seems to be command field
> - * 1 - 30 deal with the x axis
> - * 31 -60 deal with the y axis
> - *
> - * Field 1 is x axis constant force
> - * Field 31 is y axis constant force
> - *
> - * other interesting fields 1,2,3,4 on x axis
> - * (same for 31,32,33,34 on y axis)
> - *
> - * 0 0 127 127 makes the joystick autocenter hard
> - *
> - * 127 0 127 127 makes the joystick loose on the right,
> - * but stops all movemnt left
> - *
> - * -127 0 -127 -127 makes the joystick loose on the left,
> - * but stops all movement right
> - *
> - * 0 0 -127 -127 makes the joystick rattle very hard
> - *
> - * I'm sure these are effects that I don't know enough about them
> - */
> +/* Ensure we remember to swap bytes (there's no sle16) */
> +typedef __s16 __bitwise lg3_s16;
>
> -struct lg3ff_device {
> - struct hid_report *report;
> -};
> +static inline lg3_s16 lg3ff_cpu_to_sle16(s16 val)
> +{
> + return (__force lg3_s16)cpu_to_le16(val);
> +}
> +
> +struct hid_lg3ff_axis {
> + lg3_s16 constant_force; /* can cancel autocenter on relevant side */
> + u8 _padding0; /* extra byte of strength? no apparent effect */
> + /* how far towards center does the effect keep pushing:
> + * 0 = no autocenter, up to:
> + * 127 = push immediately on any deflection
> + * <0 = repel center
> + */
> + s8 autocenter_strength;
> + /* how hard does autocenter push */
> + s8 autocenter_force;
> + /* damping with force of autocenter_force (see also damper_*) */
> + s8 autocenter_damping;
> + lg3_s16 spring_deadzone_neg; /* for offset center, set these equal */
> + lg3_s16 spring_deadzone_pos;
> + s8 spring_coeff_neg; /* <0 repels center */
> + s8 spring_coeff_pos;
> + lg3_s16 spring_saturation;
> + u8 _padding1[8]; /* [4-8]: a different way of autocentering? */
> + s8 damper_coeff_neg;
> + s8 damper_coeff_pos;
> + lg3_s16 damper_saturation;
> + u8 _padding2[4]; /* seems to do the same as damper*? */
> +} __packed;
> +
> +struct hid_lg3ff_report {
> + struct hid_lg3ff_axis x;
> + struct hid_lg3ff_axis y;
> + u8 _padding[3];
> +} __packed;
> +
> +#define FF_REPORT_ID 2
> +
> +static void hig_lg3ff_send(struct input_dev *idev,
> + struct hid_lg3ff_report *raw_rep)
> +{
> + struct hid_device *hid = input_get_drvdata(idev);
> + struct hid_report *hid_rep = hid->report_enum[HID_OUTPUT_REPORT]
> + .report_id_hash[FF_REPORT_ID];
> + int i;
> +
> + /* We can be called while atomic (via hid_lg3ff_play) and must queue;
> + * there's nowhere to enqueue a raw report, so populate a hid_report.
> + */
> + for (i = 0; i < sizeof(*raw_rep); i++)
> + hid_rep->field[0]->value[i] = ((u8 *)raw_rep)[i];
> + hid_hw_request(hid, hid_rep, HID_REQ_SET_REPORT);
> +}
>
> static int hid_lg3ff_play(struct input_dev *dev, void *data,
> struct ff_effect *effect)
> {
> - struct hid_device *hid = input_get_drvdata(dev);
> - struct list_head *report_list = &hid->report_enum[HID_OUTPUT_REPORT].report_list;
> - struct hid_report *report = list_entry(report_list->next, struct hid_report, list);
> - int x, y;
> -
> -/*
> - * Available values in the field should always be 63, but we only use up to
> - * 35. Instead, clear the entire area, however big it is.
> - */
> - memset(report->field[0]->value, 0,
> - sizeof(__s32) * report->field[0]->report_count);
> + struct hid_lg3ff_report report = {0};
> + s16 x, y;
>
> switch (effect->type) {
> case FF_CONSTANT:
> @@ -78,46 +96,32 @@ static int hid_lg3ff_play(struct input_dev *dev, void *data,
> * Already clamped in ff_memless
> * 0 is center (different then other logitech)
> */
> - x = effect->u.ramp.start_level;
> - y = effect->u.ramp.end_level;
> -
> - /* send command byte */
> - report->field[0]->value[0] = 0x51;
> + x = -effect->u.ramp.start_level << 8;
> + y = -effect->u.ramp.end_level << 8;
>
> /*
> * Sign backwards from other Force3d pro
> * which get recast here in two's complement 8 bits
> */
> - report->field[0]->value[1] = (unsigned char)(-x);
> - report->field[0]->value[31] = (unsigned char)(-y);
> -
> - hid_hw_request(hid, report, HID_REQ_SET_REPORT);
> + report.x.constant_force = lg3ff_cpu_to_sle16(x);
> + report.y.constant_force = lg3ff_cpu_to_sle16(y);
> + hig_lg3ff_send(dev, &report);
> break;
> }
> return 0;
> }
> static void hid_lg3ff_set_autocenter(struct input_dev *dev, u16 magnitude)
> {
> - struct hid_device *hid = input_get_drvdata(dev);
> - struct list_head *report_list = &hid->report_enum[HID_OUTPUT_REPORT].report_list;
> - struct hid_report *report = list_entry(report_list->next, struct hid_report, list);
> + struct hid_lg3ff_report report = {0};
>
> -/*
> - * Auto Centering probed from device
> - * NOTE: deadman's switch on G940 must be covered
> - * for effects to work
> - */
> - report->field[0]->value[0] = 0x51;
> - report->field[0]->value[1] = 0x00;
> - report->field[0]->value[2] = 0x00;
> - report->field[0]->value[3] = 0x7F;
> - report->field[0]->value[4] = 0x7F;
> - report->field[0]->value[31] = 0x00;
> - report->field[0]->value[32] = 0x00;
> - report->field[0]->value[33] = 0x7F;
> - report->field[0]->value[34] = 0x7F;
> -
> - hid_hw_request(hid, report, HID_REQ_SET_REPORT);
> + /* negative means repel from center, so scale to 0-127 */
> + s8 mag_scaled = magnitude >> 9;
> +
> + report.x.autocenter_strength = 127;
> + report.x.autocenter_force = mag_scaled;
> + report.y.autocenter_strength = 127;
> + report.y.autocenter_force = mag_scaled;
> + hig_lg3ff_send(dev, &report);
> }
>
>
> @@ -136,7 +140,9 @@ int lg3ff_init(struct hid_device *hid)
> int i;
>
> /* Check that the report looks ok */
> - if (!hid_validate_values(hid, HID_OUTPUT_REPORT, 0, 0, 35))
> + BUILD_BUG_ON(sizeof(struct hid_lg3ff_report) != 63); /* excl. id */
> + if (!hid_validate_values(hid, HID_OUTPUT_REPORT, FF_REPORT_ID, 0,
> + sizeof(struct hid_lg3ff_report)))
> return -ENODEV;
>
> /* Assume single fixed device G940 */
> @@ -147,8 +153,10 @@ int lg3ff_init(struct hid_device *hid)
> if (error)
> return error;
>
> - if (test_bit(FF_AUTOCENTER, dev->ffbit))
> + if (test_bit(FF_AUTOCENTER, dev->ffbit)) {
> dev->ff->set_autocenter = hid_lg3ff_set_autocenter;
> + hid_lg3ff_set_autocenter(dev, 0);
> + }
>
> hid_info(hid, "Force feedback for Logitech Flight System G940 by Gary Stein <LordCnidarian@xxxxxxxxx>\n");
> return 0;
> --
> 2.17.1
>
>
> --
> Chris Boyle
> https://chris.boyle.name/
>
--
Jiri Kosina
SUSE Labs
