[PARISC] Use work queue in LED/LCD driver instead of tasklet.

2.6.12-rc1-pa6 use work queue in LED/LCD driver instead of tasklet.

Main advantage is it allows use of msleep() in the led_LCD_driver to
"atomically" perform two MMIO writes (CMD, then DATA).
Lead to nice cleanup of the main led_work_func() and led_LCD_driver().
Kudos to David for being persistent.

From: David Pye <dmp@davidmpye.dyndns.org>
Signed-off-by: Grant Grundler <grundler@parisc-linux.org>
Signed-off-by: Kyle McMartin <kyle@parisc-linux.org>

arch/parisc/kernel/time.c

@@ -89,14 +89,6 @@ irqreturn_t timer_interrupt(int irq, void *dev_id, struct pt_regs *regs)
 		}
 	}
     
-#ifdef CONFIG_CHASSIS_LCD_LED
-	/* Only schedule the led tasklet on cpu 0, and only if it
-	 * is enabled.
-	 */
-	if (cpu == 0 && !atomic_read(&led_tasklet.count))
-		tasklet_schedule(&led_tasklet);
-#endif
-
 	/* check soft power switch status */
 	if (cpu == 0 && !atomic_read(&power_tasklet.count))
 		tasklet_schedule(&power_tasklet);

drivers/parisc/led.c

@@ -18,6 +18,9 @@
  * Changes:
  *      - Audit copy_from_user in led_proc_write.
  *                                Daniele Bellucci <bellucda@tiscali.it>
+ *	- Switch from using a tasklet to a work queue, so the led_LCD_driver
+ *	  	can sleep.
+ *	  			  David Pye <dmp@davidmpye.dyndns.org>
  */
 
 #include <linux/config.h>
@@ -37,6 +40,7 @@
 #include <linux/proc_fs.h>
 #include <linux/ctype.h>
 #include <linux/blkdev.h>
+#include <linux/workqueue.h>
 #include <linux/rcupdate.h>
 #include <asm/io.h>
 #include <asm/processor.h>
@@ -47,25 +51,30 @@
 #include <asm/uaccess.h>
 
 /* The control of the LEDs and LCDs on PARISC-machines have to be done 
-   completely in software. The necessary calculations are done in a tasklet
-   which is scheduled at every timer interrupt and since the calculations 
-   may consume relatively much CPU-time some of the calculations can be 
+   completely in software. The necessary calculations are done in a work queue
+   task which is scheduled regularly, and since the calculations may consume a 
+   relatively large amount of CPU time, some of the calculations can be 
    turned off with the following variables (controlled via procfs) */
 
 static int led_type = -1;
-static int led_heartbeat = 1;
-static int led_diskio = 1;
-static int led_lanrxtx = 1;
+static unsigned char lastleds;	/* LED state from most recent update */
+static unsigned int led_heartbeat = 1;
+static unsigned int led_diskio = 1;
+static unsigned int led_lanrxtx = 1;
 static char lcd_text[32];
 static char lcd_text_default[32];
 
+
+static struct workqueue_struct *led_wq;
+static void led_work_func(void *);
+static DECLARE_WORK(led_task, led_work_func, NULL);
+
 #if 0
 #define DPRINTK(x)	printk x
 #else
 #define DPRINTK(x)
 #endif
 
-
 struct lcd_block {
 	unsigned char command;	/* stores the command byte      */
 	unsigned char on;	/* value for turning LED on     */
@@ -116,12 +125,27 @@ lcd_info __attribute__((aligned(8))) =
 #define LCD_DATA_REG	lcd_info.lcd_data_reg_addr	 
 #define LED_DATA_REG	lcd_info.lcd_cmd_reg_addr	/* LASI & ASP only */
 
+#define LED_HASLCD 1
+#define LED_NOLCD  0
+
+/* The workqueue must be created at init-time */
+static int start_task(void) 
+{	
+	/* Display the default text now */
+	if (led_type == LED_HASLCD) lcd_print( lcd_text_default );
+
+	/* Create the work queue and queue the LED task */
+	led_wq = create_singlethread_workqueue("led_wq");	
+	queue_work(led_wq, &led_task);
+
+	return 0;
+}
+
+device_initcall(start_task);
 
 /* ptr to LCD/LED-specific function */
 static void (*led_func_ptr) (unsigned char);
 
-#define LED_HASLCD 1
-#define LED_NOLCD  0
 #ifdef CONFIG_PROC_FS
 static int led_proc_read(char *page, char **start, off_t off, int count, 
 	int *eof, void *data)
@@ -287,51 +311,34 @@ static void led_LASI_driver(unsigned char leds)
    ** 
    ** led_LCD_driver()
    **   
-   ** The logic of the LCD driver is, that we write at every scheduled call
-   ** only to one of LCD_CMD_REG _or_ LCD_DATA_REG - registers.
-   ** That way we don't need to let this tasklet busywait for min_cmd_delay
-   ** milliseconds.
-   **
-   ** TODO: check the value of "min_cmd_delay" against the value of HZ.
-   **   
  */
 static void led_LCD_driver(unsigned char leds)
 {
-	static int last_index;	/* 0:heartbeat, 1:disk, 2:lan_in, 3:lan_out */
-	static int last_was_cmd;/* 0: CMD was written last, 1: DATA was last */
-	struct lcd_block *block_ptr;
-	int value;
-
-	switch (last_index) {
-	    case 0:	block_ptr = &lcd_info.heartbeat;
-			value = leds & LED_HEARTBEAT;
-			break;
-	    case 1:	block_ptr = &lcd_info.disk_io;
-			value = leds & LED_DISK_IO;
-			break;					
-	    case 2:	block_ptr = &lcd_info.lan_rcv;
-			value = leds & LED_LAN_RCV;
-			break;					
-	    case 3:	block_ptr = &lcd_info.lan_tx;
-			value = leds & LED_LAN_TX;
-			break;
-	    default:	/* should never happen: */
-			return;
-	}
+	static int i;
+	static unsigned char mask[4] = { LED_HEARTBEAT, LED_DISK_IO,
+		LED_LAN_RCV, LED_LAN_TX };
 	
-	if (last_was_cmd) {
-	    /* write the value to the LCD data port */
-    	    gsc_writeb( value ? block_ptr->on : block_ptr->off, LCD_DATA_REG );
-	} else {
-	    /* write the command-byte to the LCD command register */
-    	    gsc_writeb( block_ptr->command, LCD_CMD_REG );
-	}    
+	static struct lcd_block * blockp[4] = {
+		&lcd_info.heartbeat,
+		&lcd_info.disk_io,
+		&lcd_info.lan_rcv,
+		&lcd_info.lan_tx
+	};
+
+	/* Convert min_cmd_delay to milliseconds */
+	unsigned int msec_cmd_delay = 1 + (lcd_info.min_cmd_delay / 1000);
+	
+	for (i=0; i<4; ++i) 
+	{
+		if ((leds & mask[i]) != (lastleds & mask[i])) 
+		{
+			gsc_writeb( blockp[i]->command, LCD_CMD_REG );
+			msleep(msec_cmd_delay);
 			
-	/* now update the vars for the next interrupt iteration */ 
-	if (++last_was_cmd == 2) { /* switch between cmd & data */
-	    last_was_cmd = 0;
-	    if (++last_index == 4) 
-		last_index = 0;	 /* switch back to heartbeat index */
+			gsc_writeb( leds & mask[i] ? blockp[i]->on : 
+					blockp[i]->off, LCD_DATA_REG );
+			msleep(msec_cmd_delay);
+		}
 	}
 }
 
@@ -356,7 +363,7 @@ static __inline__ int led_get_net_activity(void)
 
 	rx_total = tx_total = 0;
 	
-	/* we are running as tasklet, so locking dev_base 
+	/* we are running as a workqueue task, so locking dev_base 
 	 * for reading should be OK */
 	read_lock(&dev_base_lock);
 	rcu_read_lock();
@@ -420,79 +427,63 @@ static __inline__ int led_get_diskio_activity(void)
 
 
 /*
-   ** led_tasklet_func()
+   ** led_work_func()
    ** 
-   ** is scheduled at every timer interrupt from time.c and
-   ** updates the chassis LCD/LED 
+   ** manages when and which chassis LCD/LED gets updated
 
     TODO:
     - display load average (older machines like 715/64 have 4 "free" LED's for that)
     - optimizations
  */
 
-#define HEARTBEAT_LEN (HZ*6/100)
-#define HEARTBEAT_2ND_RANGE_START (HZ*22/100)
+#define HEARTBEAT_LEN (HZ*10/100)
+#define HEARTBEAT_2ND_RANGE_START (HZ*28/100)
 #define HEARTBEAT_2ND_RANGE_END   (HEARTBEAT_2ND_RANGE_START + HEARTBEAT_LEN)
 
-#define NORMALIZED_COUNT(count) (count/(HZ/100))
+#define LED_UPDATE_INTERVAL (1 + (HZ*19/1000))
 
-static void led_tasklet_func(unsigned long unused)
+static void led_work_func (void *unused)
 {
-	static unsigned char lastleds;
-	unsigned char currentleds; /* stores current value of the LEDs */
-	static unsigned long count; /* static incremented value, not wrapped */
+	static unsigned long last_jiffies;
 	static unsigned long count_HZ; /* counter in range 0..HZ */
+	unsigned char currentleds = 0; /* stores current value of the LEDs */
 
 	/* exit if not initialized */
 	if (!led_func_ptr)
 	    return;
 
-	/* increment the local counters */
-	++count;
-	if (++count_HZ == HZ)
+	/* increment the heartbeat timekeeper */
+	count_HZ += jiffies - last_jiffies;
+	last_jiffies = jiffies;
+	if (count_HZ >= HZ)
 	    count_HZ = 0;
 
-	currentleds = lastleds;
-
-	if (led_heartbeat)
+	if (likely(led_heartbeat))
 	{
-		/* flash heartbeat-LED like a real heart (2 x short then a long delay) */
-		if (count_HZ<HEARTBEAT_LEN || 
-		    (count_HZ>=HEARTBEAT_2ND_RANGE_START && count_HZ<HEARTBEAT_2ND_RANGE_END)) 
+		/* flash heartbeat-LED like a real heart
+		 * (2 x short then a long delay)
+		 */
+		if (count_HZ < HEARTBEAT_LEN || 
+				(count_HZ >= HEARTBEAT_2ND_RANGE_START &&
+				count_HZ < HEARTBEAT_2ND_RANGE_END)) 
 			currentleds |= LED_HEARTBEAT;
-		else
-		    currentleds &= ~LED_HEARTBEAT;
-	}
-
-	/* look for network activity and flash LEDs respectively */
-	if (led_lanrxtx && ((NORMALIZED_COUNT(count)+(8/2)) & 7) == 0)
-	{
-		currentleds &= ~(LED_LAN_RCV | LED_LAN_TX);
-		currentleds |= led_get_net_activity();
 	}
 
-	/* avoid to calculate diskio-stats at same irq  as netio-stats */
-	if (led_diskio && (NORMALIZED_COUNT(count) & 7) == 0)
-	{
-		currentleds &= ~LED_DISK_IO;
-		currentleds |= led_get_diskio_activity();
-	}
+	if (likely(led_lanrxtx))  currentleds |= led_get_net_activity();
+	if (likely(led_diskio))   currentleds |= led_get_diskio_activity();
 
 	/* blink all LEDs twice a second if we got an Oops (HPMC) */
-	if (oops_in_progress) {
+	if (unlikely(oops_in_progress)) 
 		currentleds = (count_HZ<=(HZ/2)) ? 0 : 0xff;
-	}
 
-	/* update the LCD/LEDs */
-	if (currentleds != lastleds) {
-	    led_func_ptr(currentleds);
+	if (currentleds != lastleds)
+	{
+		led_func_ptr(currentleds);	/* Update the LCD/LEDs */
 		lastleds = currentleds;
 	}
-}
-
-/* main led tasklet struct (scheduled from time.c) */
-DECLARE_TASKLET_DISABLED(led_tasklet, led_tasklet_func, 0);
 
+	queue_delayed_work(led_wq, &led_task, LED_UPDATE_INTERVAL);
+}
 
 /*
    ** led_halt()
@@ -522,8 +513,12 @@ static int led_halt(struct notifier_block *nb, unsigned long event, void *buf)
 	default:		return NOTIFY_DONE;
 	}
 	
-	/* completely stop the LED/LCD tasklet */
-	tasklet_disable(&led_tasklet);
+	/* Cancel the work item and delete the queue */
+	if (led_wq) {
+		cancel_rearming_delayed_workqueue(led_wq, &led_task);
+		destroy_workqueue(led_wq);
+		led_wq = NULL;
+	}
  
 	if (lcd_info.model == DISPLAY_MODEL_LCD)
 		lcd_print(txt);
@@ -559,7 +554,6 @@ int __init register_led_driver(int model, unsigned long cmd_reg, unsigned long d
 		printk(KERN_INFO "LCD display at %lx,%lx registered\n", 
 			LCD_CMD_REG , LCD_DATA_REG);
 		led_func_ptr = led_LCD_driver;
-		lcd_print( lcd_text_default );
 		led_type = LED_HASLCD;
 		break;
 
@@ -589,8 +583,10 @@ int __init register_led_driver(int model, unsigned long cmd_reg, unsigned long d
 	initialized++;
 	register_reboot_notifier(&led_notifier);
 
-	/* start the led tasklet for the first time */
-	tasklet_enable(&led_tasklet);
+	/* Ensure the work is queued */
+	if (led_wq) {
+		queue_work(led_wq, &led_task);
+	}
 
 	return 0;
 }
@@ -626,8 +622,8 @@ void __init register_led_regions(void)
    ** lcd_print()
    ** 
    ** Displays the given string on the LCD-Display of newer machines.
-   ** lcd_print() disables the timer-based led tasklet during its 
-   ** execution and enables it afterwards again.
+   ** lcd_print() disables/enables the timer-based led work queue to
+   ** avoid a race condition while writing the CMD/DATA register pair.
    **
  */
 int lcd_print( char *str )
@@ -637,8 +633,9 @@ int lcd_print( char *str )
 	if (!led_func_ptr || lcd_info.model != DISPLAY_MODEL_LCD)
 	    return 0;
 	
-	/* temporarily disable the led tasklet */
-	tasklet_disable(&led_tasklet);
+	/* temporarily disable the led work task */
+	if (led_wq)
+		cancel_rearming_delayed_workqueue(led_wq, &led_task);
 
 	/* copy display string to buffer for procfs */
 	strlcpy(lcd_text, str, sizeof(lcd_text));
@@ -656,8 +653,10 @@ int lcd_print( char *str )
 	    udelay(lcd_info.min_cmd_delay);
 	}
 	
-	/* re-enable the led tasklet */
-	tasklet_enable(&led_tasklet);
+	/* re-queue the work */
+	if (led_wq) {
+		queue_work(led_wq, &led_task);
+	}
 
 	return lcd_info.lcd_width;
 }

include/asm-parisc/led.h

@@ -23,9 +23,6 @@
 
 #define LED_CMD_REG_NONE 0		/* NULL == no addr for the cmd register */
 
-/* led tasklet struct */
-extern struct tasklet_struct led_tasklet;
-
 /* register_led_driver() */
 int __init register_led_driver(int model, unsigned long cmd_reg, unsigned long data_reg);