ptp: add debugfs interface to see applied channel masks

Use debugfs to be able to view channel mask applied to every timestamp
event queue.

Every time the device is opened, a new entry is created in
`$DEBUGFS_MOUNTPOINT/ptpN/$INSTANCE_ADDRESS/mask`.

The mask value can be viewed grouped in 32bit decimal values using cat,
or converted to hexadecimal with the included `ptpchmaskfmt.sh` script.
32 bit values are listed from least significant to most significant.

Signed-off-by: Xabier Marquiegui <[e-mail]>
Suggested-by: Vinicius Costa Gomes <[e-mail]>
Signed-off-by: David S. Miller <[e-mail]>

drivers/ptp/ptp_chardev.c

···
 #include <linux/sched.h>
 #include <linux/slab.h>
 #include <linux/timekeeping.h>
+#include <linux/debugfs.h>
 
 #include <linux/nospec.h>
 
···
 	struct ptp_clock *ptp =
 		container_of(pccontext->clk, struct ptp_clock, clock);
 	struct timestamp_event_queue *queue;
+	char debugfsname[32];
 
 	queue = kzalloc(sizeof(*queue), GFP_KERNEL);
 	if (!queue)
···
 	spin_lock_init(&queue->lock);
 	list_add_tail(&queue->qlist, &ptp->tsevqs);
 	pccontext->private_clkdata = queue;
+
+	/* Debugfs contents */
+	sprintf(debugfsname, "0x%p", queue);
+	queue->debugfs_instance =
+		debugfs_create_dir(debugfsname, ptp->debugfs_root);
+	queue->dfs_bitmap.array = (u32 *)queue->mask;
+	queue->dfs_bitmap.n_elements =
+		DIV_ROUND_UP(PTP_MAX_CHANNELS, BITS_PER_BYTE * sizeof(u32));
+	debugfs_create_u32_array("mask", 0444, queue->debugfs_instance,
+				 &queue->dfs_bitmap);
+
 	return 0;
 }
 
···
 	unsigned long flags;
 
 	if (queue) {
+		debugfs_remove(queue->debugfs_instance);
 		pccontext->private_clkdata = NULL;
 		spin_lock_irqsave(&queue->lock, flags);
 		list_del(&queue->qlist);

drivers/ptp/ptp_clock.c

···
 #include <linux/slab.h>
 #include <linux/syscalls.h>
 #include <linux/uaccess.h>
+#include <linux/debugfs.h>
 #include <uapi/linux/sched/types.h>
 
 #include "ptp_private.h"
···
 	spin_unlock_irqrestore(&tsevq->lock, flags);
 	bitmap_free(tsevq->mask);
 	kfree(tsevq);
+	debugfs_remove(ptp->debugfs_root);
 	ida_free(&ptp_clocks_map, ptp->index);
 	kfree(ptp);
 }
···
 	struct ptp_clock *ptp;
 	struct timestamp_event_queue *queue = NULL;
 	int err = 0, index, major = MAJOR(ptp_devt);
+	char debugfsname[8];
 	size_t size;
 
 	if (info->n_alarm > PTP_MAX_ALARMS)
···
 		pr_err("failed to create posix clock\n");
 		return ERR_PTR(err);
 	}
+
+	/* Debugfs initialization */
+	sprintf(debugfsname, "ptp%d", ptp->index);
+	ptp->debugfs_root = debugfs_create_dir(debugfsname, NULL);
 
 	return ptp;
 

drivers/ptp/ptp_private.h

···
 #include <linux/time.h>
 #include <linux/list.h>
 #include <linux/bitmap.h>
+#include <linux/debugfs.h>
 
 #define PTP_MAX_TIMESTAMPS 128
 #define PTP_BUF_TIMESTAMPS 30
···
 	spinlock_t lock;
 	struct list_head qlist;
 	unsigned long *mask;
+	struct dentry *debugfs_instance;
+	struct debugfs_u32_array dfs_bitmap;
 };
 
 struct ptp_clock {
···
 	struct mutex n_vclocks_mux; /* protect concurrent n_vclocks access */
 	bool is_virtual_clock;
 	bool has_cycles;
+	struct dentry *debugfs_root;
 };
 
 #define info_to_vclock(d) container_of((d), struct ptp_vclock, info)

tools/testing/selftests/ptp/ptpchmaskfmt.sh

···
+#!/bin/bash
+# SPDX-License-Identifier: GPL-2.0
+
+# Simple helper script to transform ptp debugfs timestamp event queue filtering
+# masks from decimal values to hexadecimal values
+
+# Only takes the debugfs mask file path as an argument
+DEBUGFS_MASKFILE="${1}"
+
+#shellcheck disable=SC2013,SC2086
+for int in $(cat "$DEBUGFS_MASKFILE") ; do
+    printf '0x%08X ' "$int"
+done
+echo