bes2600: self-detect when firmware does not honor PSM and skip the cycle

The c6 series fixed several host-side bookkeeping bugs around PSM
transitions, but didn't address the underlying contract: this chip's
firmware (BES2600 with the Bestechnic Dec 2023 build that ships on
PineTab2 and most danctnix images) silently drops every WSM_set_pm
request without emitting the corresponding PM_INDICATION. The driver's
own power_down_work delayed work calls bes2600_pwr_enter_lp_mode every
~10s; without firmware acknowledgment each call burns 5s on
wait_for_completion_timeout(pm_enter_cmpl, 5*HZ) and produces a
recurring three-line cascade in dmesg:

  bes2600_pwr_enter_lp_mode, wait pm ind timeout
  bes2600_sdio_active failed, subsys:0
  bes2600_pwr_device_exit_lp_mode, active mcu fail

Confirmed by tripwire instrumentation on PineTab2 (linux-pinetab2
6.19.10-danctnix1, ohm) running the c5+c6 stack: zero
wsm_set_pm_indication() invocations across an entire boot, while
bes2600_pwr_enter_lp_mode timed out repeatedly, and
bes2600_sdio_active() consistently saw BES_SLAVE_STATUS_REG_ID return
0x2f (every "ready" bit set except MCU_WAKEUP_READY (bit 4) - the
firmware reports "I'm awake, there's nothing to wake from").

This patch makes the driver self-heal:

  * struct bes2600_pwr_t gains pm_unsupported (bool) and
    pm_consecutive_timeouts (unsigned int). Both initialised to
    0/false.

  * bes2600_pwr_enter_lp_mode early-returns -EOPNOTSUPP when
    pm_unsupported is set. Skips the per-VIF set_pm round-trip and
    the wait_for_completion entirely.

  * On the cmpxchg-success branch of the timeout path, we increment
    pm_consecutive_timeouts. When it crosses
    BES2600_PM_UNSUPPORTED_THRESHOLD (3, ~15s of trying), we latch
    pm_unsupported = true and force chip_pm_state = ACTIVE so that
    bes2600_pwr_device_exit_lp_mode's c6.2 skip branch covers the
    wake side (no gpio_wake / sbus_active / WSM_set_operational_mode
    reissue past the first one).

  * bes2600_pwr_notify_ps_changed resets pm_consecutive_timeouts to 0
    on any incoming PM indication, and clears pm_unsupported if it
    was previously latched. So a firmware update that fixes PM_IND
    delivery automatically re-enables PSM transitions without a
    driver rebuild.

mac80211's PSM requests via bes2600_set_pm() still flow to the
firmware unchanged; they just don't have host-side timeouts so they
remain silent regardless of firmware acknowledgment. Power
consumption goes up if the firmware actually CAN do PSM (we'd be
keeping the chip awake unnecessarily), but on a chip where the
counter trips this trade-off is forced anyway: the chip stayed awake
under the broken cascade as well, just with constant SDIO churn.

Net effect on dmesg: after ~15s of boot, the three-line cascade stops
firing entirely. The firmware-side wedge is observed once per boot
(captured by the pm_unsupported latch) instead of per-cycle.

Signed-off-by: Markus Fritsche <fritsche.markus@gmail.com>

bes2600/bes_pwr.c

@@ -467,6 +467,45 @@ static void bes2600_pwr_device_enter_lp_mode(struct bes2600_common *hw_priv)
 	bes_devel("device enter sleep\n");
 }
 
+/*
+ * Number of consecutive bes2600_pwr_enter_lp_mode timeouts (with zero
+ * PM_INDICATIONs received) before we conclude the firmware does not
+ * honor host-driven PSM and switch to a sticky skip path.
+ */
+#define BES2600_PM_UNSUPPORTED_THRESHOLD	3
+
+/*
+ * Latch pm_unsupported = true and force chip_pm_state = ACTIVE so the
+ * c6.2 wake-side skip branch covers bes2600_pwr_device_exit_lp_mode.
+ * Called after BES2600_PM_UNSUPPORTED_THRESHOLD consecutive enter_lp_mode
+ * timeouts with zero PM_INDICATIONs.
+ */
+static void bes2600_pwr_latch_pm_unsupported(struct bes2600_common *hw_priv)
+{
+	bes_warn("PSM not honored (%u timeouts), switching to skip mode\n",
+		 hw_priv->bes_power.pm_consecutive_timeouts);
+	hw_priv->bes_power.pm_unsupported = true;
+	atomic_set(&hw_priv->bes_power.chip_pm_state,
+		   BES2600_CHIP_PM_ACTIVE);
+
+	/*
+	 * Hold the MCU wake-flag bit permanently. Without this, every
+	 * sdio_rx_work invocation hits bes2600_gpio_wakeup_mcu(SDIO_RX)
+	 * when gpio_wakup_flags == 0, drives the GPIO high and msleeps
+	 * 10 ms per RX. With ~50 RX/s of beacons + multicast that's
+	 * ~50%% of the bes_sdio workqueue thread blocked in msleep,
+	 * which directly caps RX throughput. Holding the MCU bit makes
+	 * those calls bit-only bookkeeping (gpio_wakeup = (flags == 0)
+	 * stays false, no GPIO toggle, no msleep). The bit is never
+	 * cleared once pm_unsupported is set because
+	 * bes2600_pwr_device_enter_lp_mode is unreachable under the
+	 * early-return.
+	 */
+	if (hw_priv->sbus_ops->gpio_wake)
+		hw_priv->sbus_ops->gpio_wake(hw_priv->sbus_priv,
+					     GPIO_WAKE_FLAG_MCU);
+}
+
 static int bes2600_pwr_enter_lp_mode(struct bes2600_common *hw_priv)
 {
 	int i = 0;
@@ -476,6 +515,17 @@ static int bes2600_pwr_enter_lp_mode(struct bes2600_common *hw_priv)
 	char ip_str[20];
 	unsigned long status = 0;
 
+	/*
+	 * Sticky early-return when we've previously concluded the firmware
+	 * doesn't honor PSM. Each attempt would otherwise burn 5s on a
+	 * doomed wait_for_completion_timeout and produce a noisy three-line
+	 * cascade in dmesg every time power_down_work retries (every
+	 * ~10s). The chip stays in active mode, which on this firmware is
+	 * the de-facto state anyway.
+	 */
+	if (hw_priv->bes_power.pm_unsupported)
+		return -EOPNOTSUPP;
+
 	/* set interface low power configuration */
 	bes2600_for_each_vif(hw_priv, priv, i) {
 #ifdef P2P_MULTIVIF
@@ -569,6 +619,9 @@ static int bes2600_pwr_enter_lp_mode(struct bes2600_common *hw_priv)
 						atomic_set(&hw_priv->bes_power.chip_pm_state,
 							   BES2600_CHIP_PM_UNKNOWN);
 						timeouts++;
+						if (++hw_priv->bes_power.pm_consecutive_timeouts
+						    >= BES2600_PM_UNSUPPORTED_THRESHOLD)
+							bes2600_pwr_latch_pm_unsupported(hw_priv);
 					}
 				}
 			} else {
@@ -607,7 +660,8 @@ static int bes2600_pwr_enter_lp_mode(struct bes2600_common *hw_priv)
 		 * GPIO stays high and the bit clear here is purely
 		 * bookkeeping (so the next gpio_wake doesn't no-op).
 		 */
-		if (hw_priv->sbus_ops->gpio_sleep)
+		if (!hw_priv->bes_power.pm_unsupported &&
+		    hw_priv->sbus_ops->gpio_sleep)
 			hw_priv->sbus_ops->gpio_sleep(hw_priv->sbus_priv,
 						      GPIO_WAKE_FLAG_MCU);
 		ret = -ETIMEDOUT;
@@ -930,6 +984,8 @@ void bes2600_pwr_init(struct bes2600_common *hw_priv)
         mutex_init(&hw_priv->bes_power.pwr_mutex);
         atomic_set(&hw_priv->bes_power.dev_state, 0);
 	atomic_set(&hw_priv->bes_power.chip_pm_state, BES2600_CHIP_PM_UNKNOWN);
+	hw_priv->bes_power.pm_unsupported = false;
+	hw_priv->bes_power.pm_consecutive_timeouts = 0;
         init_completion(&hw_priv->bes_power.pm_enter_cmpl);
         sema_init(&hw_priv->bes_power.sync_lock, 1);
         device_set_wakeup_capable(hw_priv->pdev, true);
@@ -1319,6 +1375,18 @@ void bes2600_pwr_notify_ps_changed(struct bes2600_common *hw_priv, u8 psmode)
 	 * indication can prime a future wait against a freshly
 	 * reinit_completion()'ed state.
 	 */
+	/*
+	 * Any PM indication, whatever its psmode, proves the firmware is
+	 * actually emitting them. Reset the consecutive-timeout counter
+	 * so a transient stall doesn't permanently disable PSM, and clear
+	 * pm_unsupported if a previous run had latched it.
+	 */
+	hw_priv->bes_power.pm_consecutive_timeouts = 0;
+	if (hw_priv->bes_power.pm_unsupported) {
+		bes_warn("PM indication arrived after pm_unsupported was set; re-enabling PSM transitions\n");
+		hw_priv->bes_power.pm_unsupported = false;
+	}
+
 	if ((psmode & 0x01) != WSM_PSM_ACTIVE) {
 		atomic_set(&hw_priv->bes_power.chip_pm_state,
 			   BES2600_CHIP_PM_LP);

bes2600/bes_pwr.h

@@ -121,6 +121,15 @@ struct bes2600_pwr_t
         struct bes2600_pwr_event_t pwr_events[BES2600_DELAY_EVENT_NUM];
         atomic_t pm_set_in_process;
 	atomic_t chip_pm_state;
+	/*
+	 * Sticky flag set after BES2600_PM_UNSUPPORTED_THRESHOLD
+	 * consecutive enter_lp_mode timeouts with zero PM_INDICATIONs
+	 * received from firmware. Indicates this chip's firmware does
+	 * not honor host-driven PSM transitions; further attempts are
+	 * skipped to avoid the 5s timeout cascade.
+	 */
+	bool pm_unsupported;
+	unsigned int pm_consecutive_timeouts;
 };
 
 #ifdef CONFIG_BES2600_WOWLAN