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From: Finn Thain <fthain@telegraphics.com.au>
To: Geert Uytterhoeven <geert@linux-m68k.org>,
	Philip Blundell <philb@gnu.org>
Cc: Andreas Schwab <schwab@linux-m68k.org>,
	Arnd Bergmann <arnd@arndb.de>,
	Stephen N Chivers <schivers@csc.com.au>,
	Thomas Gleixner <tglx@linutronix.de>,
	Daniel Lezcano <daniel.lezcano@linaro.org>,
	Michael Schmitz <schmitzmic@gmail.com>,
	John Stultz <john.stultz@linaro.org>,
	Linus Walleij <linus.walleij@linaro.org>,
	linux-m68k@lists.linux-m68k.org, linux-kernel@vger.kernel.org
Subject: [RFC PATCH v2 09/14] m68k: hp300: Remove hp300_gettimeoffset()
Date: Mon, 19 Nov 2018 12:10:38 +1100	[thread overview]
Message-ID: <eb676d37a8e40b88f6c577b372b6512bc19a3394.1542589838.git.fthain@telegraphics.com.au> (raw)
In-Reply-To: <cover.1542589838.git.fthain@telegraphics.com.au>

hp300_gettimeoffset() never checks the timer interrupt flag and will
fail to notice when the timer counter gets reloaded. That means the
clock could jump backwards.

Remove this code and leave this platform on the 'jiffies' clocksource.
Note that this amounts to a regression in clock precision. However,
adopting the 'jiffies' clocksource does resolve the monotonicity issue.

Signed-off-by: Finn Thain <fthain@telegraphics.com.au>
---
hp300_gettimeoffset() cannot be used in a clocksource conversion
unless it can be made monotonic. I can't fix this without knowing the
details of the timer implementation, such as the relationship between
the timer count and the interrupt flag.
---
 arch/m68k/hp300/time.c | 19 -------------------
 1 file changed, 19 deletions(-)

diff --git a/arch/m68k/hp300/time.c b/arch/m68k/hp300/time.c
index d30b03ea93a2..37cccdb46def 100644
--- a/arch/m68k/hp300/time.c
+++ b/arch/m68k/hp300/time.c
@@ -31,9 +31,6 @@
 #define	CLKMSB2		0x9
 #define	CLKMSB3		0xD
 
-/* This is for machines which generate the exact clock. */
-#define USECS_PER_JIFFY (1000000/HZ)
-
 #define INTVAL ((10000 / 4) - 1)
 
 static irqreturn_t hp300_tick(int irq, void *dev_id)
@@ -53,22 +50,6 @@ static irqreturn_t hp300_tick(int irq, void *dev_id)
 	return IRQ_HANDLED;
 }
 
-u32 hp300_gettimeoffset(void)
-{
-  /* Read current timer 1 value */
-  unsigned char lsb, msb1, msb2;
-  unsigned short ticks;
-
-  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);
-  return ((USECS_PER_JIFFY * ticks) / INTVAL) * 1000;
-}
-
 void __init hp300_sched_init(irq_handler_t vector)
 {
   out_8(CLOCKBASE + CLKCR2, 0x1);		/* select CR1 */
-- 
2.18.1


  reply	other threads:[~2018-11-19  1:22 UTC|newest]

Thread overview: 40+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-11-19  1:10 [RFC PATCH v2 00/14] m68k: Drop arch_gettimeoffset and adopt clocksource API Finn Thain
2018-11-19  1:10 ` Finn Thain [this message]
2018-11-20  9:09   ` [RFC PATCH v2 09/14] m68k: hp300: Remove hp300_gettimeoffset() Kars de Jong
2018-11-20 23:13     ` Finn Thain
2018-11-21  8:10       ` Geert Uytterhoeven
2018-11-21  8:41         ` Finn Thain
2018-11-21  8:55           ` Geert Uytterhoeven
2018-11-21  9:47             ` Finn Thain
2018-11-21 10:02               ` Geert Uytterhoeven
2018-11-21 11:14                 ` Finn Thain
2018-11-25  1:15                   ` Finn Thain
2018-11-25  2:44                     ` Michael Schmitz
2018-11-25  3:25                       ` Finn Thain
2018-11-21  8:22       ` Kars de Jong
2018-11-19  1:10 ` [RFC PATCH v2 07/14] m68k: atari: Convert to clocksource API Finn Thain
2018-11-19  8:35   ` Michael Schmitz
2018-11-20  8:10   ` Linus Walleij
2018-11-20  8:19     ` Geert Uytterhoeven
2018-11-20  9:30     ` Finn Thain
2018-11-20  9:53       ` Linus Walleij
2018-11-20 10:02     ` Andreas Schwab
2018-11-24  2:03       ` Michael Schmitz
2018-11-24  3:08         ` Finn Thain
2018-11-19  1:10 ` [RFC PATCH v2 08/14] m68k: bvme6000: " Finn Thain
2018-11-19  1:10 ` [RFC PATCH v2 11/14] m68k: mvme147: " Finn Thain
2018-11-19  1:10 ` [RFC PATCH v2 10/14] m68k: mac: " Finn Thain
2018-11-20  8:15   ` Linus Walleij
2018-11-20  9:00     ` Finn Thain
2018-11-20  9:59       ` Linus Walleij
2018-11-19  1:10 ` [RFC PATCH v2 04/14] m68k: apollo, q40, sun3, sun3x: Remove arch_gettimeoffset implementations Finn Thain
2018-11-19  1:10 ` [RFC PATCH v2 01/14] m68k: Call timer_interrupt() with interrupts disabled Finn Thain
2018-11-19  1:10 ` [RFC PATCH v2 03/14] m68k: mac: Clean up unused timer definitions Finn Thain
2018-11-20  1:02   ` Finn Thain
2018-11-19  1:10 ` [RFC PATCH v2 12/14] m68k: mvme147: Handle timer counter overflow Finn Thain
2018-11-19  1:10 ` [RFC PATCH v2 13/14] m68k: mvme16x: Convert to clocksource API Finn Thain
2018-11-19  1:10 ` [RFC PATCH v2 02/14] m68k: mac: Fix VIA timer counter accesses Finn Thain
2018-11-19  1:10 ` [RFC PATCH v2 06/14] m68k: amiga: Convert to clocksource API Finn Thain
2018-11-20  8:04   ` Linus Walleij
2018-11-19  1:10 ` [RFC PATCH v2 05/14] m68k: Drop ARCH_USES_GETTIMEOFFSET Finn Thain
2018-11-19  1:10 ` [RFC PATCH v2 14/14] m68k: mvme16x: Handle timer counter overflow Finn Thain

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