Commit 4be2ba93 authored by Finn Thain's avatar Finn Thain Committed by Geert Uytterhoeven
Browse files

m68k: hp300: Handle timer counter overflow 



Because hp300_read_clk() never checks the timer interrupt flag it may
fail to notice that the timer has wrapped, allowing the clock to jump
backwards. This is not a new problem.

This is resolved by checking the interrupt flag and, if need be,
taking wrap-around into account. The interrupt handler clears the flag
when it eventually executes.

Signed-off-by: default avatarFinn Thain <fthain@telegraphics.com.au>
Signed-off-by: default avatarGeert Uytterhoeven <geert@linux-m68k.org>
parent 2ed16626

arch/m68k/hp300/time.c

+27 −19
Original line number Diff line number Diff line
@@ -30,7 +30,7 @@ static struct clocksource hp300_clk = { 
	.flags  = CLOCK_SOURCE_IS_CONTINUOUS,

};



static u32 clk_total;

static u32 clk_total, clk_offset;



/* Clock hardware definitions */
@@ -41,9 +41,12 @@ static u32 clk_total; 
#define	CLKCR3		CLKCR1

#define	CLKSR		CLKCR2

#define	CLKMSB1		0x5

#define	CLKLSB1		0x7

#define	CLKMSB2		0x9

#define	CLKMSB3		0xD



#define	CLKSR_INT1	BIT(0)



/* This is for machines which generate the exact clock. */



#define HP300_TIMER_CLOCK_FREQ 250000
@@ -60,6 +63,7 @@ static irqreturn_t hp300_tick(int irq, void *dev_id) 
	in_8(CLOCKBASE + CLKSR);

	asm volatile ("movpw %1@(5),%0" : "=d" (tmp) : "a" (CLOCKBASE));

	clk_total += INTVAL;

	clk_offset = 0;

	timer_routine(0, NULL);

	local_irq_restore(flags);
@@ -71,20 +75,24 @@ static irqreturn_t hp300_tick(int irq, void *dev_id) 
static u64 hp300_read_clk(struct clocksource *cs)

{

	unsigned long flags;

  unsigned char lsb, msb1, msb2;

	unsigned char lsb, msb, msb_new;

	u32 ticks;



	local_irq_save(flags);

	/* Read current timer 1 value */

  msb1 = in_8(CLOCKBASE + 5);

  lsb = in_8(CLOCKBASE + 7);

  msb2 = in_8(CLOCKBASE + 5);

  if (msb1 != msb2)

    /* A carry happened while we were reading.  Read it again */

    lsb = in_8(CLOCKBASE + 7);



  ticks = INTVAL - ((msb2 << 8) | lsb);

  ticks += clk_total;

	msb = in_8(CLOCKBASE + CLKMSB1);

again:

	if ((in_8(CLOCKBASE + CLKSR) & CLKSR_INT1) && msb > 0)

		clk_offset = INTVAL;

	lsb = in_8(CLOCKBASE + CLKLSB1);

	msb_new = in_8(CLOCKBASE + CLKMSB1);

	if (msb_new != msb) {

		msb = msb_new;

		goto again;

	}



	ticks = INTVAL - ((msb << 8) | lsb);

	ticks += clk_offset + clk_total;

	local_irq_restore(flags);



	return ticks;

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