clocksource/drivers/fttmr010: Fix invalid interrupt register access

TIMER_INTR_MASK register (Base Address of Timer + 0x38) is not designed
for masking interrupts on ast2500 chips, and it's not even listed in
ast2400 datasheet, so it's not safe to access TIMER_INTR_MASK on aspeed
chips.

Similarly, TIMER_INTR_STATE register (Base Address of Timer + 0x34) is
not interrupt status register on ast2400 and ast2500 chips. Although
there is no side effect to reset the register in fttmr010_common_init(),
it's just misleading to do so.

Besides, "count_down" is renamed to "is_aspeed" in "fttmr010" structure,
and more comments are added so the code is more readble.

Signed-off-by: Tao Ren <[e-mail]>
Reviewed-by: Linus Walleij <[e-mail]>
Signed-off-by: Daniel Lezcano <[e-mail]>

drivers/clocksource/timer-fttmr010.c

···
 #include <linux/delay.h>
 
 /*
- * Register definitions for the timers
+ * Register definitions common for all the timer variants.
  */
 #define TIMER1_COUNT		(0x00)
 #define TIMER1_LOAD		(0x04)
···
 #define TIMER3_MATCH1		(0x28)
 #define TIMER3_MATCH2		(0x2c)
 #define TIMER_CR		(0x30)
-#define TIMER_INTR_STATE	(0x34)
-#define TIMER_INTR_MASK		(0x38)
 
+/*
+ * Control register (TMC30) bit fields for fttmr010/gemini/moxart timers.
+ */
 #define TIMER_1_CR_ENABLE	BIT(0)
 #define TIMER_1_CR_CLOCK	BIT(1)
 #define TIMER_1_CR_INT		BIT(2)
···
 #define TIMER_3_CR_UPDOWN	BIT(11)
 
 /*
- * The Aspeed AST2400 moves bits around in the control register
- * and lacks bits for setting the timer to count upwards.
+ * Control register (TMC30) bit fields for aspeed ast2400/ast2500 timers.
+ * The aspeed timers move bits around in the control register and lacks
+ * bits for setting the timer to count upwards.
  */
 #define TIMER_1_CR_ASPEED_ENABLE	BIT(0)
 #define TIMER_1_CR_ASPEED_CLOCK		BIT(1)
···
 #define TIMER_3_CR_ASPEED_CLOCK		BIT(9)
 #define TIMER_3_CR_ASPEED_INT		BIT(10)
 
+/*
+ * Interrupt status/mask register definitions for fttmr010/gemini/moxart
+ * timers.
+ * The registers don't exist and they are not needed on aspeed timers
+ * because:
+ *   - aspeed timer overflow interrupt is controlled by bits in Control
+ *     Register (TMC30).
+ *   - aspeed timers always generate interrupt when either one of the
+ *     Match registers equals to Status register.
+ */
+#define TIMER_INTR_STATE	(0x34)
+#define TIMER_INTR_MASK		(0x38)
 #define TIMER_1_INT_MATCH1	BIT(0)
 #define TIMER_1_INT_MATCH2	BIT(1)
 #define TIMER_1_INT_OVERFLOW	BIT(2)
···
 struct fttmr010 {
 	void __iomem *base;
 	unsigned int tick_rate;
-	bool count_down;
+	bool is_aspeed;
 	u32 t1_enable_val;
 	struct clock_event_device clkevt;
 #ifdef CONFIG_ARM
···
 	cr &= ~fttmr010->t1_enable_val;
 	writel(cr, fttmr010->base + TIMER_CR);
 
-	if (fttmr010->count_down) {
+	if (fttmr010->is_aspeed) {
 		/*
 		 * ASPEED Timer Controller will load TIMER1_LOAD register
 		 * into TIMER1_COUNT register when the timer is re-enabled.
···
 
 	/* Setup counter start from 0 or ~0 */
 	writel(0, fttmr010->base + TIMER1_COUNT);
-	if (fttmr010->count_down)
+	if (fttmr010->is_aspeed) {
 		writel(~0, fttmr010->base + TIMER1_LOAD);
-	else
+	} else {
 		writel(0, fttmr010->base + TIMER1_LOAD);
 
-	/* Enable interrupt */
-	cr = readl(fttmr010->base + TIMER_INTR_MASK);
-	cr &= ~(TIMER_1_INT_OVERFLOW | TIMER_1_INT_MATCH2);
-	cr |= TIMER_1_INT_MATCH1;
-	writel(cr, fttmr010->base + TIMER_INTR_MASK);
+		/* Enable interrupt */
+		cr = readl(fttmr010->base + TIMER_INTR_MASK);
+		cr &= ~(TIMER_1_INT_OVERFLOW | TIMER_1_INT_MATCH2);
+		cr |= TIMER_1_INT_MATCH1;
+		writel(cr, fttmr010->base + TIMER_INTR_MASK);
+	}
 
 	return 0;
 }
···
 	writel(cr, fttmr010->base + TIMER_CR);
 
 	/* Setup timer to fire at 1/HZ intervals. */
-	if (fttmr010->count_down) {
+	if (fttmr010->is_aspeed) {
 		writel(period, fttmr010->base + TIMER1_LOAD);
-		writel(0, fttmr010->base + TIMER1_MATCH1);
 	} else {
 		cr = 0xffffffff - (period - 1);
 		writel(cr, fttmr010->base + TIMER1_COUNT);
···
 	}
 
 	/*
-	 * The Aspeed AST2400 moves bits around in the control register,
-	 * otherwise it works the same.
+	 * The Aspeed timers move bits around in the control register.
 	 */
 	if (is_aspeed) {
 		fttmr010->t1_enable_val = TIMER_1_CR_ASPEED_ENABLE |
 			TIMER_1_CR_ASPEED_INT;
-		/* Downward not available */
-		fttmr010->count_down = true;
+		fttmr010->is_aspeed = true;
 	} else {
 		fttmr010->t1_enable_val = TIMER_1_CR_ENABLE | TIMER_1_CR_INT;
-	}
 
-	/*
-	 * Reset the interrupt mask and status
-	 */
-	writel(TIMER_INT_ALL_MASK, fttmr010->base + TIMER_INTR_MASK);
-	writel(0, fttmr010->base + TIMER_INTR_STATE);
+		/*
+		 * Reset the interrupt mask and status
+		 */
+		writel(TIMER_INT_ALL_MASK, fttmr010->base + TIMER_INTR_MASK);
+		writel(0, fttmr010->base + TIMER_INTR_STATE);
+	}
 
 	/*
 	 * Enable timer 1 count up, timer 2 count up, except on Aspeed,
···
 	if (is_aspeed)
 		val = TIMER_2_CR_ASPEED_ENABLE;
 	else {
-		val = TIMER_2_CR_ENABLE;
-		if (!fttmr010->count_down)
-			val |= TIMER_1_CR_UPDOWN | TIMER_2_CR_UPDOWN;
+		val = TIMER_2_CR_ENABLE | TIMER_1_CR_UPDOWN |
+			TIMER_2_CR_UPDOWN;
 	}
 	writel(val, fttmr010->base + TIMER_CR);
 
···
 	writel(0, fttmr010->base + TIMER2_MATCH1);
 	writel(0, fttmr010->base + TIMER2_MATCH2);
 
-	if (fttmr010->count_down) {
+	if (fttmr010->is_aspeed) {
 		writel(~0, fttmr010->base + TIMER2_LOAD);
 		clocksource_mmio_init(fttmr010->base + TIMER2_COUNT,
 				      "FTTMR010-TIMER2",
···
 
 #ifdef CONFIG_ARM
 	/* Also use this timer for delays */
-	if (fttmr010->count_down)
+	if (fttmr010->is_aspeed)
 		fttmr010->delay_timer.read_current_timer =
 			fttmr010_read_current_timer_down;
 	else