From: Doug Anderson <dianders@chromium.org>
To: Wim Van Sebroeck <wim@iguana.be>, Guenter Roeck <linux@roeck-us.net>
Cc: Leela Krishna Amudala <l.krishna@samsung.com>,
Olof Johansson <olof@lixom.net>,
Tomasz Figa <tomasz.figa@gmail.com>,
Kukjin Kim <kgene.kim@samsung.com>,
Doug Anderson <dianders@chromium.org>,
Ben Dooks <ben-linux@fluff.org>,
linux-arm-kernel@lists.infradead.org,
linux-samsung-soc@vger.kernel.org,
linux-watchdog@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout
Date: Tue, 26 Nov 2013 10:30:37 -0800 [thread overview]
Message-ID: <1385490637-10306-1-git-send-email-dianders@chromium.org> (raw)
The existing watchdog timeout worked OK but didn't deal with
rounding in an ideal way when dividing out all of its clocks.
Specifically if you had a timeout of 32 seconds and an input clock of
66666666, you'd end up setting a timeout of 31.9998 seconds and
reporting a timeout of 31 seconds.
Specifically DBG printouts showed:
s3c2410wdt_set_heartbeat: count=16666656, timeout=32, freq=520833
s3c2410wdt_set_heartbeat: timeout=32, divisor=255, count=16666656 (0000ff4f)
and the final timeout reported to the user was:
((count / divisor) * divisor) / freq
(0xff4f * 255) / 520833 = 31 (truncated from 31.9998)
the technically "correct" value is:
(0xff4f * 255) / (66666666.0 / 128) = 31.9998
By using "DIV_ROUND_UP" we can be a little more correct.
s3c2410wdt_set_heartbeat: count=16666688, timeout=32, freq=520834
s3c2410wdt_set_heartbeat: timeout=32, divisor=255, count=16666688 (0000ff50)
and the final timeout reported to the user:
(0xff50 * 255) / 520834 = 32
the technically "correct" value is:
(0xff50 * 255) / (66666666.0 / 128) = 32.0003
We'll use a DIV_ROUND_UP to solve this, generally erroring on the side
of reporting shorter values to the user and setting the watchdog to
slightly longer than requested:
* Round input frequency up to assume watchdog is counting faster.
* Round divisions by divisor up to give us extra time.
Signed-off-by: Doug Anderson <dianders@chromium.org>
---
drivers/watchdog/s3c2410_wdt.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
index 7d8fd04..fe2322b 100644
--- a/drivers/watchdog/s3c2410_wdt.c
+++ b/drivers/watchdog/s3c2410_wdt.c
@@ -188,7 +188,7 @@ static int s3c2410wdt_set_heartbeat(struct watchdog_device *wdd, unsigned timeou
if (timeout < 1)
return -EINVAL;
- freq /= 128;
+ freq = DIV_ROUND_UP(freq, 128);
count = timeout * freq;
DBG("%s: count=%d, timeout=%d, freq=%lu\n",
@@ -201,20 +201,20 @@ static int s3c2410wdt_set_heartbeat(struct watchdog_device *wdd, unsigned timeou
if (count >= 0x10000) {
for (divisor = 1; divisor <= 0x100; divisor++) {
- if ((count / divisor) < 0x10000)
+ if (DIV_ROUND_UP(count, divisor) < 0x10000)
break;
}
- if ((count / divisor) >= 0x10000) {
+ if (divisor > 0x100) {
dev_err(wdt->dev, "timeout %d too big\n", timeout);
return -EINVAL;
}
}
DBG("%s: timeout=%d, divisor=%d, count=%d (%08x)\n",
- __func__, timeout, divisor, count, count/divisor);
+ __func__, timeout, divisor, count, DIV_ROUND_UP(count, divisor));
- count /= divisor;
+ count = DIV_ROUND_UP(count, divisor);
wdt->count = count;
/* update the pre-scaler */
--
1.8.4.1
WARNING: multiple messages have this Message-ID (diff)
From: Doug Anderson <dianders@chromium.org>
To: Wim Van Sebroeck <wim@iguana.be>, Guenter Roeck <linux@roeck-us.net>
Cc: Kukjin Kim <kgene.kim@samsung.com>,
linux-watchdog@vger.kernel.org,
Leela Krishna Amudala <l.krishna@samsung.com>,
linux-kernel@vger.kernel.org, Tomasz Figa <tomasz.figa@gmail.com>,
Doug Anderson <dianders@chromium.org>,
linux-samsung-soc@vger.kernel.org,
Ben Dooks <ben-linux@fluff.org>, Olof Johansson <olof@lixom.net>,
linux-arm-kernel@lists.infradead.org
Subject: [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout
Date: Tue, 26 Nov 2013 10:30:37 -0800 [thread overview]
Message-ID: <1385490637-10306-1-git-send-email-dianders@chromium.org> (raw)
The existing watchdog timeout worked OK but didn't deal with
rounding in an ideal way when dividing out all of its clocks.
Specifically if you had a timeout of 32 seconds and an input clock of
66666666, you'd end up setting a timeout of 31.9998 seconds and
reporting a timeout of 31 seconds.
Specifically DBG printouts showed:
s3c2410wdt_set_heartbeat: count=16666656, timeout=32, freq=520833
s3c2410wdt_set_heartbeat: timeout=32, divisor=255, count=16666656 (0000ff4f)
and the final timeout reported to the user was:
((count / divisor) * divisor) / freq
(0xff4f * 255) / 520833 = 31 (truncated from 31.9998)
the technically "correct" value is:
(0xff4f * 255) / (66666666.0 / 128) = 31.9998
By using "DIV_ROUND_UP" we can be a little more correct.
s3c2410wdt_set_heartbeat: count=16666688, timeout=32, freq=520834
s3c2410wdt_set_heartbeat: timeout=32, divisor=255, count=16666688 (0000ff50)
and the final timeout reported to the user:
(0xff50 * 255) / 520834 = 32
the technically "correct" value is:
(0xff50 * 255) / (66666666.0 / 128) = 32.0003
We'll use a DIV_ROUND_UP to solve this, generally erroring on the side
of reporting shorter values to the user and setting the watchdog to
slightly longer than requested:
* Round input frequency up to assume watchdog is counting faster.
* Round divisions by divisor up to give us extra time.
Signed-off-by: Doug Anderson <dianders@chromium.org>
---
drivers/watchdog/s3c2410_wdt.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
index 7d8fd04..fe2322b 100644
--- a/drivers/watchdog/s3c2410_wdt.c
+++ b/drivers/watchdog/s3c2410_wdt.c
@@ -188,7 +188,7 @@ static int s3c2410wdt_set_heartbeat(struct watchdog_device *wdd, unsigned timeou
if (timeout < 1)
return -EINVAL;
- freq /= 128;
+ freq = DIV_ROUND_UP(freq, 128);
count = timeout * freq;
DBG("%s: count=%d, timeout=%d, freq=%lu\n",
@@ -201,20 +201,20 @@ static int s3c2410wdt_set_heartbeat(struct watchdog_device *wdd, unsigned timeou
if (count >= 0x10000) {
for (divisor = 1; divisor <= 0x100; divisor++) {
- if ((count / divisor) < 0x10000)
+ if (DIV_ROUND_UP(count, divisor) < 0x10000)
break;
}
- if ((count / divisor) >= 0x10000) {
+ if (divisor > 0x100) {
dev_err(wdt->dev, "timeout %d too big\n", timeout);
return -EINVAL;
}
}
DBG("%s: timeout=%d, divisor=%d, count=%d (%08x)\n",
- __func__, timeout, divisor, count, count/divisor);
+ __func__, timeout, divisor, count, DIV_ROUND_UP(count, divisor));
- count /= divisor;
+ count = DIV_ROUND_UP(count, divisor);
wdt->count = count;
/* update the pre-scaler */
--
1.8.4.1
WARNING: multiple messages have this Message-ID (diff)
From: dianders@chromium.org (Doug Anderson)
To: linux-arm-kernel@lists.infradead.org
Subject: [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout
Date: Tue, 26 Nov 2013 10:30:37 -0800 [thread overview]
Message-ID: <1385490637-10306-1-git-send-email-dianders@chromium.org> (raw)
The existing watchdog timeout worked OK but didn't deal with
rounding in an ideal way when dividing out all of its clocks.
Specifically if you had a timeout of 32 seconds and an input clock of
66666666, you'd end up setting a timeout of 31.9998 seconds and
reporting a timeout of 31 seconds.
Specifically DBG printouts showed:
s3c2410wdt_set_heartbeat: count=16666656, timeout=32, freq=520833
s3c2410wdt_set_heartbeat: timeout=32, divisor=255, count=16666656 (0000ff4f)
and the final timeout reported to the user was:
((count / divisor) * divisor) / freq
(0xff4f * 255) / 520833 = 31 (truncated from 31.9998)
the technically "correct" value is:
(0xff4f * 255) / (66666666.0 / 128) = 31.9998
By using "DIV_ROUND_UP" we can be a little more correct.
s3c2410wdt_set_heartbeat: count=16666688, timeout=32, freq=520834
s3c2410wdt_set_heartbeat: timeout=32, divisor=255, count=16666688 (0000ff50)
and the final timeout reported to the user:
(0xff50 * 255) / 520834 = 32
the technically "correct" value is:
(0xff50 * 255) / (66666666.0 / 128) = 32.0003
We'll use a DIV_ROUND_UP to solve this, generally erroring on the side
of reporting shorter values to the user and setting the watchdog to
slightly longer than requested:
* Round input frequency up to assume watchdog is counting faster.
* Round divisions by divisor up to give us extra time.
Signed-off-by: Doug Anderson <dianders@chromium.org>
---
drivers/watchdog/s3c2410_wdt.c | 10 +++++-----
1 file changed, 5 insertions(+), 5 deletions(-)
diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
index 7d8fd04..fe2322b 100644
--- a/drivers/watchdog/s3c2410_wdt.c
+++ b/drivers/watchdog/s3c2410_wdt.c
@@ -188,7 +188,7 @@ static int s3c2410wdt_set_heartbeat(struct watchdog_device *wdd, unsigned timeou
if (timeout < 1)
return -EINVAL;
- freq /= 128;
+ freq = DIV_ROUND_UP(freq, 128);
count = timeout * freq;
DBG("%s: count=%d, timeout=%d, freq=%lu\n",
@@ -201,20 +201,20 @@ static int s3c2410wdt_set_heartbeat(struct watchdog_device *wdd, unsigned timeou
if (count >= 0x10000) {
for (divisor = 1; divisor <= 0x100; divisor++) {
- if ((count / divisor) < 0x10000)
+ if (DIV_ROUND_UP(count, divisor) < 0x10000)
break;
}
- if ((count / divisor) >= 0x10000) {
+ if (divisor > 0x100) {
dev_err(wdt->dev, "timeout %d too big\n", timeout);
return -EINVAL;
}
}
DBG("%s: timeout=%d, divisor=%d, count=%d (%08x)\n",
- __func__, timeout, divisor, count, count/divisor);
+ __func__, timeout, divisor, count, DIV_ROUND_UP(count, divisor));
- count /= divisor;
+ count = DIV_ROUND_UP(count, divisor);
wdt->count = count;
/* update the pre-scaler */
--
1.8.4.1
next reply other threads:[~2013-11-26 18:35 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2013-11-26 18:30 Doug Anderson [this message]
2013-11-26 18:30 ` [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout Doug Anderson
2013-11-26 18:30 ` Doug Anderson
2013-11-26 18:48 ` Guenter Roeck
2013-11-26 18:48 ` Guenter Roeck
2013-11-26 21:34 ` Doug Anderson
2013-11-26 21:34 ` Doug Anderson
2013-11-26 21:34 ` Doug Anderson
2013-11-27 0:10 ` Guenter Roeck
2013-11-27 0:10 ` Guenter Roeck
2013-11-27 0:10 ` Guenter Roeck
2013-11-27 0:57 ` Doug Anderson
2013-11-27 0:57 ` Doug Anderson
2013-11-27 0:57 ` Doug Anderson
2013-11-27 0:57 ` Doug Anderson
2013-11-27 0:57 ` [PATCH v2] " Doug Anderson
2013-11-27 0:57 ` Doug Anderson
2013-11-27 1:04 ` Guenter Roeck
2013-11-27 1:04 ` Guenter Roeck
2014-01-08 20:03 ` Wim Van Sebroeck
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