bes2600: recover wedged firmware via mmc_hw_reset on link break

When the LMAC active monitor detects 'link break between lmac and host'
(the hw_buf_used==pending watchdog in bes2600_bh_lmac_active_monitor),
bes2600_chrdev_wifi_force_close(hw_priv, true) is invoked to tear the
device down and prepare for a fresh probe. On the wifi_force_close_work
side this calls bes2600_chrdev_do_system_close() which dispatches
sbus_ops->power_switch(0).

On PineTab2 (RK3566 + BES2600WM over SDIO) this recovery path is a
no-op:

  * bes2600_sdio_power_down() writes a SYSTEM_CLOSE host-int message,
    clears MMC_CAP_NONREMOVABLE, and schedules sdio_scan_work, which is
    the literal one-line stub bes_warn("...this function does
    nothing\n").
  * bes2600_sdio_on() (the eventual power_switch(1) counterpart)
    toggles pdata->powerup, which is NULL on PineTab2 because the
    wifi-reset GPIO is owned by sdio_pwrseq, not the bes2600 device
    tree node (see arch/arm64/boot/dts/rockchip/rk3566-pinetab2.dtsi:
    'The reset pin is claimed by sdio_mmcseq, It is better to move it
    to U-Boot so the OS can use it.').

Net result: the chip is never reset. The function drivers are not
removed (the SDIO core has no signal that the card is gone), the
firmware stays wedged, and a subsequent rmmod bes2600 leaves the SDIO
function in a half-torn-down state. modprobe bes2600 then fails with
'probe with driver bes2600_wlan failed with error -123' (-ENOMEDIUM)
on both functions (:1 wifi, :2 BT-companion) until a full system
reboot.

Observed on PineTab2 (linux-pinetab2 6.19.10-danctnix1-1) after ~150
minutes of background-scan rejects (wsm_generic_confirm 0x0007,
[SCAN] Scan failed (-22)) accumulating until the LMAC stopped
acknowledging TX buffers (hw_buf_used:24 pending:24). Reproducible
under sustained scan pressure.

Add a sbus operation bus_reset() that the recovery path can call when
power_switch() has no effective chip-reset signal of its own. Provide
an SDIO implementation that calls mmc_hw_reset(self->func->card),
which on a multi-function SDIO card (PineTab2 binds func 1 for WLAN
and func 2 for the BT-companion path) takes the remove-and-rescan
path: mmc_sdio_hw_reset() marks the card removed and schedules
mmc_rescan, which tears down the bound function drivers and re-detects
the card on the next sweep, in turn reinvoking bes2600_sdio_probe().
With a single function probed it instead invokes mmc_power_cycle()
directly, which on PineTab2 toggles the wifi-reset GPIO via
sdio_pwrseq.

Add bes2600_chrdev_do_bus_reset() as the chrdev-side helper. It
invokes the bus op and then waits on probe_done_wq for the SDIO
remove() callback to clear sbus_priv, mirroring the wait pattern
already used by bes2600_chrdev_do_system_close() so that a subsequent
bes2600_switch_wifi(true) sees a clean state and can wait on the
fresh probe.

Wire it into bes2600_chrdev_wifi_force_close_work(): when halt_dev is
set (the hard-exception path used by both
bes2600_bh_lmac_active_monitor and bes2600_bh_mcu_active_monitor) and
the underlying bus implements bus_reset, take the new recovery path;
otherwise fall back to the legacy power_switch(0) sequence so this
patch is a no-op on USB or any other future bus that does not provide
bus_reset.

mmc_hw_reset() is exported by the MMC core and is the canonical
recovery primitive; calling it without holding the SDIO host claim is
correct because the multi-func remove-and-rescan path acquires the
host claim via the mmc workqueue, and the single-func mmc_power_cycle
path does not require the host claim.

No DT change is required: this works against the existing PineTab2
DTS, where the wifi-reset GPIO and the optional sdio_pwrkey GPIO (on
v2.0 boards) are both already configured as MMC pwrseq resets.

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

bes2600/bes_chardev.c

@@ -442,6 +442,48 @@ int bes2600_chrdev_do_system_close(const struct sbus_ops *sbus_ops, struct sbus_
 	return ret;
 }
 
+/*
+ * Hard-reset the bus and wait for the bus core to remove the chip.
+ *
+ * Used by the firmware-wedge recovery path on platforms where the normal
+ * power_switch(0) sequence has no effective chip-reset signal. The bus
+ * implementation triggers an asynchronous re-detect; this helper waits for
+ * the resulting remove() callback to clear bes2600_cdev.sbus_priv so that a
+ * subsequent bes2600_switch_wifi(true) sees a clean state and can wait on
+ * the fresh probe.
+ */
+int bes2600_chrdev_do_bus_reset(const struct sbus_ops *sbus_ops, struct sbus_priv *priv)
+{
+	int ret;
+	long status;
+
+	if (!sbus_ops || !priv)
+		return -EINVAL;
+
+	if (!sbus_ops->bus_reset)
+		return -EOPNOTSUPP;
+
+	bes_info("trigger bus reset to recover wedged firmware.\n");
+
+	ret = sbus_ops->bus_reset(priv);
+	if (ret) {
+		bes_err("bus_reset failed: %d\n", ret);
+		return ret;
+	}
+
+	/*
+	 * The bus reset is asynchronous: the bus core schedules a rescan
+	 * which removes the bound function drivers and then re-detects the
+	 * chip. Wait for the remove callback to clear sbus_priv. Do not
+	 * dereference 'priv' after this point -- it may already be freed.
+	 */
+	status = wait_event_timeout(bes2600_cdev.probe_done_wq,
+				    !bes2600_cdev.sbus_priv, HZ * 3);
+	WARN_ON(status <= 0);
+
+	return 0;
+}
+
 bool bes2600_chrdev_is_wifi_opened(void)
 {
 	bool wifi_opened = false;
@@ -540,8 +582,21 @@ static void bes2600_chrdev_wifi_force_close_work(struct work_struct *work)
 		/* unregister wifi */
 		bes2600_switch_wifi(0);
 
-		/* power down device if wifi is only opened */
-		if (bes2600_chrdev_check_system_close()) {
+		/*
+		 * Hard exception with a bus_reset implementation: tear the
+		 * bus down via mmc_hw_reset() (or equivalent) so the next
+		 * bringup probes a freshly reset chip. On PineTab2 this is
+		 * the only effective recovery path -- the existing
+		 * power_switch(0)/(1) sequence has no chip-reset signal of
+		 * its own (sdio_pwrseq owns wifi_reset).
+		 *
+		 * Soft close, or hard close on a board without bus_reset:
+		 * fall back to the legacy power_switch(0) sequence.
+		 */
+		if (bes2600_cdev.halt_dev && bes2600_cdev.sbus_ops->bus_reset) {
+			bes2600_chrdev_do_bus_reset(bes2600_cdev.sbus_ops,
+						    bes2600_cdev.sbus_priv);
+		} else if (bes2600_chrdev_check_system_close()) {
 			bes2600_chrdev_do_system_close(bes2600_cdev.sbus_ops,
 						bes2600_cdev.sbus_priv);
 		}