block/floppy: Convert callback to pass timer_list

In preparation for unconditionally passing the struct timer_list pointer to
all timer callbacks, switch to passing in the timer pointer explicitly.
Calculate the drive from the offset of the timer in the timer list.

Cc: Jiri Kosina <jikos@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Ming Lei <tom.leiming@gmail.com>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Geliang Tang <geliangtang@gmail.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/block/floppy.c

@@ -903,10 +903,14 @@ static void unlock_fdc(void)
 }
 
 /* switches the motor off after a given timeout */
-static void motor_off_callback(unsigned long nr)
+static void motor_off_callback(struct timer_list *t)
 {
+	unsigned long nr = t - motor_off_timer;
 	unsigned char mask = ~(0x10 << UNIT(nr));
 
+	if (WARN_ON_ONCE(nr >= N_DRIVE))
+		return;
+
 	set_dor(FDC(nr), mask, 0);
 }
 
@@ -3047,7 +3051,7 @@ static void raw_cmd_done(int flag)
 		else
 			raw_cmd->flags &= ~FD_RAW_DISK_CHANGE;
 		if (raw_cmd->flags & FD_RAW_NO_MOTOR_AFTER)
-			motor_off_callback(current_drive);
+			motor_off_callback(&motor_off_timer[current_drive]);
 
 		if (raw_cmd->next &&
 		    (!(raw_cmd->flags & FD_RAW_FAILURE) ||
@@ -4542,7 +4546,7 @@ static int __init do_floppy_init(void)
 		disks[drive]->fops = &floppy_fops;
 		sprintf(disks[drive]->disk_name, "fd%d", drive);
 
-		setup_timer(&motor_off_timer[drive], motor_off_callback, drive);
+		timer_setup(&motor_off_timer[drive], motor_off_callback, 0);
 	}
 
 	err = register_blkdev(FLOPPY_MAJOR, "fd");