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/bes2600_sdio.c

@@ -16,6 +16,7 @@
 #include <linux/mmc/host.h>
 #include <linux/mmc/sdio_func.h>
 #include <linux/mmc/card.h>
+#include <linux/mmc/core.h>
 #include <linux/mmc/sdio.h>
 #include <linux/spinlock.h>
 #include <net/mac80211.h>
@@ -1777,6 +1778,33 @@ static void bes2600_sdio_halt_device(struct sbus_priv *self)
 	sdio_work_debug(self);
 }
 
+/*
+ * Trigger an SDIO bus reset via mmc_hw_reset().
+ *
+ * With multiple SDIO functions probed (PineTab2 binds func 1 for WLAN and
+ * func 2 for the BT-companion path) mmc_sdio_hw_reset() takes the
+ * remove-and-rescan path: it 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.
+ *
+ * In both cases the chip ends up in a freshly reset state, which is the
+ * goal of the recovery path.
+ *
+ * mmc_hw_reset() must be called without holding the SDIO host claim --
+ * the multi-func remove-and-rescan path acquires the host claim via the
+ * mmc workqueue.
+ */
+static int bes2600_sdio_bus_reset(struct sbus_priv *self)
+{
+	if (!self || !self->func || !self->func->card)
+		return -EINVAL;
+
+	return mmc_hw_reset(self->func->card);
+}
+
 static bool bes2600_sdio_wakeup_source(struct sbus_priv *self)
 {
 	struct bes2600_platform_data_sdio *pdata = bes2600_get_platform_data();
@@ -1815,6 +1843,7 @@ static struct sbus_ops bes2600_sdio_sbus_ops = {
 	.gpio_sleep		= bes2600_gpio_allow_mcu_sleep,
 	.halt_device		= bes2600_sdio_halt_device,
 	.wakeup_source		= bes2600_sdio_wakeup_source,
+	.bus_reset		= bes2600_sdio_bus_reset,
 };
 
 static void bes2600_sdio_en_lp_cb(struct bes2600_common *hw_priv)