[PATCH] HID: nintendo: fix rumble starved by the input report cadence gate

[Alexandre Derumier <aderumier@gmail.com>]

Rumble on third-party controllers speaking the Switch protocol is weak
and intermittent over bluetooth, and absent on some units.

Since commit d750d1480362 ("HID: nintendo: fix rumble rate limiter"),
joycon_enforce_subcmd_rate() requires JC_SUBCMD_VALID_DELTA_REQ (3)
consecutive input reports spaced 8-17ms apart before releasing a
subcommand. That window is the official Pro Controller's bluetooth
cadence, and controllers that do not report on it cannot pass the gate,
so their rumble is starved.

Measured over bluetooth on one host, reading the controller directly,
fraction of reports at which the requirement is met:

  official Pro Controller     95%
  Datafrog clone              46-52%
  8BitDo Pro 2                2.5-4%

The Pro 2 delivers reports in pairs, so 11-19% of its deltas are 0ms and
reset the counter. Affected controllers report Nintendo's USB IDs, and
the MAC is no better: the Datafrog clone reports an OUI registered to
Nintendo, so identifying them by vendor would misclassify it.

Instead, notice when the requirement cannot be met: after
JC_SUBCMD_RATE_MAX_FAILURES exhaustions of the limiter, fall back to the
pre-d750d1480362 throttle, which keeps the 25ms spacing and the
transmit-after-receive synchronisation from commit e93363f716a2 ("HID:
nintendo: ratelimit subcommands and rumble") and drops only the cadence
requirement. Exhaustions are counted cumulatively, as an affected
controller meets the requirement occasionally and a consecutive count
would never be reached.

Signed-off-by: Alexandre Derumier <aderumier@gmail.com>
---
 drivers/hid/hid-nintendo.c | 39 +++++++++++++++++++++++++++++++++++++-
 1 file changed, 38 insertions(+), 1 deletion(-)

diff --git a/drivers/hid/hid-nintendo.c b/drivers/hid/hid-nintendo.c
index 0000000..0000000 100644
--- a/drivers/hid/hid-nintendo.c
+++ b/drivers/hid/hid-nintendo.c
@@ -609,6 +609,8 @@ struct joycon_ctlr {
 	unsigned int last_input_report_msecs;
 	unsigned int last_subcmd_sent_msecs;
 	unsigned int consecutive_valid_report_deltas;
+	unsigned int subcmd_rate_exhaustions;
+	bool subcmd_rate_relaxed;
 
 	/* factory calibration data */
 	struct joycon_stick_cal left_stick_cal_x;
@@ -841,10 +843,11 @@ static void joycon_wait_for_input_report(struct joycon_ctlr *ctlr)
 #define JC_SUBCMD_TX_OFFSET_MS		4
 #define JC_SUBCMD_VALID_DELTA_REQ	3
 #define JC_SUBCMD_RATE_MAX_ATTEMPTS	25
+#define JC_SUBCMD_RATE_MAX_FAILURES	4
 #define JC_SUBCMD_RATE_LIMITER_USB_MS	20
 #define JC_SUBCMD_RATE_LIMITER_BT_MS	60
 #define JC_SUBCMD_RATE_LIMITER_MS(ctlr)	((ctlr)->hdev->bus == BUS_USB ? JC_SUBCMD_RATE_LIMITER_USB_MS : JC_SUBCMD_RATE_LIMITER_BT_MS)
-static void joycon_enforce_subcmd_rate(struct joycon_ctlr *ctlr)
+static void joycon_enforce_subcmd_rate_strict(struct joycon_ctlr *ctlr)
 {
 	unsigned int current_ms;
 	unsigned long subcmd_delta;
@@ -872,6 +875,14 @@ static void joycon_enforce_subcmd_rate(struct joycon_ctlr *ctlr)
 
 	if (attempts >= JC_SUBCMD_RATE_MAX_ATTEMPTS) {
 		hid_warn(ctlr->hdev, "%s: exceeded max attempts", __func__);
+
+		if (++ctlr->subcmd_rate_exhaustions == JC_SUBCMD_RATE_MAX_FAILURES) {
+			ctlr->subcmd_rate_relaxed = true;
+			hid_info(ctlr->hdev,
+				 "input report cadence does not fit the %d-%dms window; using the legacy subcommand throttle\n",
+				 JC_INPUT_REPORT_MIN_DELTA,
+				 JC_INPUT_REPORT_MAX_DELTA);
+		}
 		return;
 	}
 
@@ -886,6 +897,32 @@ static void joycon_enforce_subcmd_rate(struct joycon_ctlr *ctlr)
 	msleep(JC_SUBCMD_TX_OFFSET_MS);
 }
 
+/* The rate limiter as it was before commit d750d1480362, without the report
+ * cadence requirement.
+ */
+static void joycon_enforce_subcmd_rate_legacy(struct joycon_ctlr *ctlr)
+{
+	static const unsigned int max_subcmd_rate_ms = 25;
+	unsigned int current_ms = jiffies_to_msecs(jiffies);
+	unsigned int delta_ms = current_ms - ctlr->last_subcmd_sent_msecs;
+
+	while (delta_ms < max_subcmd_rate_ms &&
+	       ctlr->ctlr_state == JOYCON_CTLR_STATE_READ) {
+		joycon_wait_for_input_report(ctlr);
+		current_ms = jiffies_to_msecs(jiffies);
+		delta_ms = current_ms - ctlr->last_subcmd_sent_msecs;
+	}
+	ctlr->last_subcmd_sent_msecs = current_ms;
+}
+
+static void joycon_enforce_subcmd_rate(struct joycon_ctlr *ctlr)
+{
+	if (ctlr->subcmd_rate_relaxed)
+		joycon_enforce_subcmd_rate_legacy(ctlr);
+	else
+		joycon_enforce_subcmd_rate_strict(ctlr);
+}
+
 static int joycon_hid_send_sync(struct joycon_ctlr *ctlr, u8 *data, size_t len,
 				u32 timeout)
 {
base-commit: 0131b508c0e2489eac6e121135988f6eeb716f19
-- 
2.51.0