ath9k: add option to reset the wifi chip via debugfs

Sometimes, in yet unknown cases the wifi chip stops working. To allow a
watchdog in userspace to easily and quickly reset the wifi chip, add the
according functionality to userspace. A reset can then be triggered
via:

  $ echo 1 > /sys/kernel/debug/ieee80211/phy0/ath9k/reset

The number of user resets can further be tracked in the row "User reset"
in the same file.

So far people usually used "iw scan" to fix ath9k chip hangs from
userspace. Which triggers the ath9k_queue_reset(), too. The reset file
however has the advantage of less overhead, which makes debugging bugs
within ath9k_queue_reset() easier.
Signed-off-by: Linus Lüssing <ll@simonwunderlich.de>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210914192515.9273-2-linus.luessing@c0d3.blue

drivers/net/wireless/ath/ath9k/debug.c

@@ -749,9 +749,9 @@ static int read_file_misc(struct seq_file *file, void *data)
 
 static int read_file_reset(struct seq_file *file, void *data)
 {
-	struct ieee80211_hw *hw = dev_get_drvdata(file->private);
-	struct ath_softc *sc = hw->priv;
+	struct ath_softc *sc = file->private;
 	static const char * const reset_cause[__RESET_TYPE_MAX] = {
+		[RESET_TYPE_USER] = "User reset",
 		[RESET_TYPE_BB_HANG] = "Baseband Hang",
 		[RESET_TYPE_BB_WATCHDOG] = "Baseband Watchdog",
 		[RESET_TYPE_FATAL_INT] = "Fatal HW Error",
@@ -779,6 +779,55 @@ static int read_file_reset(struct seq_file *file, void *data)
 	return 0;
 }
 
+static int open_file_reset(struct inode *inode, struct file *f)
+{
+	return single_open(f, read_file_reset, inode->i_private);
+}
+
+static ssize_t write_file_reset(struct file *file,
+				const char __user *user_buf,
+				size_t count, loff_t *ppos)
+{
+	struct ath_softc *sc = file_inode(file)->i_private;
+	struct ath_hw *ah = sc->sc_ah;
+	struct ath_common *common = ath9k_hw_common(ah);
+	unsigned long val;
+	char buf[32];
+	ssize_t len;
+
+	len = min(count, sizeof(buf) - 1);
+	if (copy_from_user(buf, user_buf, len))
+		return -EFAULT;
+
+	buf[len] = '\0';
+	if (kstrtoul(buf, 0, &val))
+		return -EINVAL;
+
+	if (val != 1)
+		return -EINVAL;
+
+	/* avoid rearming hw_reset_work on shutdown */
+	mutex_lock(&sc->mutex);
+	if (test_bit(ATH_OP_INVALID, &common->op_flags)) {
+		mutex_unlock(&sc->mutex);
+		return -EBUSY;
+	}
+
+	ath9k_queue_reset(sc, RESET_TYPE_USER);
+	mutex_unlock(&sc->mutex);
+
+	return count;
+}
+
+static const struct file_operations fops_reset = {
+	.read = seq_read,
+	.write = write_file_reset,
+	.open = open_file_reset,
+	.owner = THIS_MODULE,
+	.llseek = seq_lseek,
+	.release = single_release,
+};
+
 void ath_debug_stat_tx(struct ath_softc *sc, struct ath_buf *bf,
 		       struct ath_tx_status *ts, struct ath_txq *txq,
 		       unsigned int flags)
@@ -1393,8 +1442,8 @@ int ath9k_init_debug(struct ath_hw *ah)
 				    read_file_queues);
 	debugfs_create_devm_seqfile(sc->dev, "misc", sc->debug.debugfs_phy,
 				    read_file_misc);
-	debugfs_create_devm_seqfile(sc->dev, "reset", sc->debug.debugfs_phy,
-				    read_file_reset);
+	debugfs_create_file("reset", 0600, sc->debug.debugfs_phy,
+			    sc, &fops_reset);
 
 	ath9k_cmn_debug_recv(sc->debug.debugfs_phy, &sc->debug.stats.rxstats);
 	ath9k_cmn_debug_phy_err(sc->debug.debugfs_phy, &sc->debug.stats.rxstats);

drivers/net/wireless/ath/ath9k/debug.h

@@ -39,6 +39,7 @@ struct fft_sample_tlv;
 #endif
 
 enum ath_reset_type {
+	RESET_TYPE_USER,
 	RESET_TYPE_BB_HANG,
 	RESET_TYPE_BB_WATCHDOG,
 	RESET_TYPE_FATAL_INT,