* [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout
@ 2013-11-26 18:30 Doug Anderson
2013-11-26 18:48 ` Guenter Roeck
2013-11-27 0:57 ` [PATCH v2] " Doug Anderson
0 siblings, 2 replies; 8+ messages in thread
From: Doug Anderson @ 2013-11-26 18:30 UTC (permalink / raw)
To: Wim Van Sebroeck, Guenter Roeck
Cc: Leela Krishna Amudala, Olof Johansson, Tomasz Figa, Kukjin Kim,
Doug Anderson, Ben Dooks, linux-arm-kernel, linux-samsung-soc,
linux-watchdog, linux-kernel
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
^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout
2013-11-26 18:30 [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout Doug Anderson
@ 2013-11-26 18:48 ` Guenter Roeck
2013-11-26 21:34 ` Doug Anderson
2013-11-27 0:57 ` [PATCH v2] " Doug Anderson
1 sibling, 1 reply; 8+ messages in thread
From: Guenter Roeck @ 2013-11-26 18:48 UTC (permalink / raw)
To: Doug Anderson, Wim Van Sebroeck
Cc: Leela Krishna Amudala, Olof Johansson, Tomasz Figa, Kukjin Kim,
Ben Dooks, linux-arm-kernel, linux-samsung-soc, linux-watchdog,
linux-kernel
On 11/26/2013 10:30 AM, Doug Anderson wrote:
> 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;
> }
>
Since you are at it,
divisor = DIV_ROUND_UP(count + 1, 0x10000);
might be faster, simpler, and easier to understand than the loop.
Otherwise looks good to me.
Guenter
> - 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 */
>
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout
2013-11-26 18:48 ` Guenter Roeck
@ 2013-11-26 21:34 ` Doug Anderson
2013-11-27 0:10 ` Guenter Roeck
0 siblings, 1 reply; 8+ messages in thread
From: Doug Anderson @ 2013-11-26 21:34 UTC (permalink / raw)
To: Guenter Roeck
Cc: Wim Van Sebroeck, Leela Krishna Amudala, Olof Johansson,
Tomasz Figa, Kukjin Kim, Ben Dooks, linux-arm-kernel,
linux-samsung-soc, linux-watchdog, linux-kernel
Guenter,
On Tue, Nov 26, 2013 at 10:48 AM, Guenter Roeck <linux@roeck-us.net> wrote:
> On 11/26/2013 10:30 AM, Doug Anderson wrote:
>>
>> 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;
>> }
>>
> Since you are at it,
> divisor = DIV_ROUND_UP(count + 1, 0x10000);
> might be faster, simpler, and easier to understand than the loop.
Way to see the forest for the trees!
Your math ends up with a slightly different result than the old code,
though. One example is when the count is 0x1ffff. You'll end up with
a divider of 2 and I'll end up with a divider of 3.
I think we just want:
divisor = DIV_ROUND_UP(count, 0xffff);
...that produces the same result as the old loop, but am curious to
know why you chose the "count + 1" and "0x10000".
Thanks!
-Doug
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout
2013-11-26 21:34 ` Doug Anderson
@ 2013-11-27 0:10 ` Guenter Roeck
2013-11-27 0:57 ` Doug Anderson
0 siblings, 1 reply; 8+ messages in thread
From: Guenter Roeck @ 2013-11-27 0:10 UTC (permalink / raw)
To: Doug Anderson
Cc: Wim Van Sebroeck, Leela Krishna Amudala, Olof Johansson,
Tomasz Figa, Kukjin Kim, Ben Dooks, linux-arm-kernel,
linux-samsung-soc, linux-watchdog, linux-kernel
On 11/26/2013 01:34 PM, Doug Anderson wrote:
> Guenter,
>
> On Tue, Nov 26, 2013 at 10:48 AM, Guenter Roeck <linux@roeck-us.net> wrote:
>> On 11/26/2013 10:30 AM, Doug Anderson wrote:
>>>
>>> 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;
>>> }
>>>
>> Since you are at it,
>> divisor = DIV_ROUND_UP(count + 1, 0x10000);
>> might be faster, simpler, and easier to understand than the loop.
>
> Way to see the forest for the trees!
>
> Your math ends up with a slightly different result than the old code,
> though. One example is when the count is 0x1ffff. You'll end up with
> a divider of 2 and I'll end up with a divider of 3.
>
> I think we just want:
>
> divisor = DIV_ROUND_UP(count, 0xffff);
>
> ...that produces the same result as the old loop, but am curious to
> know why you chose the "count + 1" and "0x10000".
>
Hi Doug,
I thought the idea was to keep (count / div) less than 0x10000, which you get
by dividing through 0x10000. 0x10000 / 0x10000 = 1, though, so I added 1
to the counter. But maybe I was thinking too much ;-).
Now, 0x1ffff / 2 = 0xffff is still lower than 0x10000, which is what
I thought is the requirement. Ultimately the error is small either way,
so DIV_ROUND_UP(count, 0xffff) is just as good to me to avoid the loop.
Thanks,
Guenter
^ permalink raw reply [flat|nested] 8+ messages in thread
* [PATCH v2] watchdog: s3c2410_wdt: Handle rounding a little better for timeout
2013-11-26 18:30 [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout Doug Anderson
2013-11-26 18:48 ` Guenter Roeck
@ 2013-11-27 0:57 ` Doug Anderson
2013-11-27 1:04 ` Guenter Roeck
2014-01-08 20:03 ` Wim Van Sebroeck
1 sibling, 2 replies; 8+ messages in thread
From: Doug Anderson @ 2013-11-27 0:57 UTC (permalink / raw)
To: Wim Van Sebroeck, Guenter Roeck
Cc: Leela Krishna Amudala, Olof Johansson, Tomasz Figa, Kukjin Kim,
Doug Anderson, Ben Dooks, linux-arm-kernel, linux-samsung-soc,
linux-watchdog, linux-kernel
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.
At the same time we can avoid a for loop by just doing the right math.
Signed-off-by: Doug Anderson <dianders@chromium.org>
---
Changes in v2:
- Avoid a for loop as per Guenter.
drivers/watchdog/s3c2410_wdt.c | 13 +++++--------
1 file changed, 5 insertions(+), 8 deletions(-)
diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
index 7d8fd04..d9bcd6e 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",
@@ -200,21 +200,18 @@ static int s3c2410wdt_set_heartbeat(struct watchdog_device *wdd, unsigned timeou
*/
if (count >= 0x10000) {
- for (divisor = 1; divisor <= 0x100; divisor++) {
- if ((count / divisor) < 0x10000)
- break;
- }
+ divisor = DIV_ROUND_UP(count, 0xffff);
- 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
^ permalink raw reply related [flat|nested] 8+ messages in thread
* Re: [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout
2013-11-27 0:10 ` Guenter Roeck
@ 2013-11-27 0:57 ` Doug Anderson
0 siblings, 0 replies; 8+ messages in thread
From: Doug Anderson @ 2013-11-27 0:57 UTC (permalink / raw)
To: Guenter Roeck
Cc: Wim Van Sebroeck, Leela Krishna Amudala, Olof Johansson,
Tomasz Figa, Kukjin Kim, Ben Dooks, linux-arm-kernel,
linux-samsung-soc, linux-watchdog, linux-kernel
Guenter,
On Tue, Nov 26, 2013 at 4:10 PM, Guenter Roeck <linux@roeck-us.net> wrote:
> On 11/26/2013 01:34 PM, Doug Anderson wrote:
>>
>> Guenter,
>>
>> On Tue, Nov 26, 2013 at 10:48 AM, Guenter Roeck <linux@roeck-us.net>
>> wrote:
>>>
>>> On 11/26/2013 10:30 AM, Doug Anderson wrote:
>>>>
>>>>
>>>> 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;
>>>> }
>>>>
>>> Since you are at it,
>>> divisor = DIV_ROUND_UP(count + 1, 0x10000);
>>> might be faster, simpler, and easier to understand than the loop.
>>
>>
>> Way to see the forest for the trees!
>>
>> Your math ends up with a slightly different result than the old code,
>> though. One example is when the count is 0x1ffff. You'll end up with
>> a divider of 2 and I'll end up with a divider of 3.
>>
>> I think we just want:
>>
>> divisor = DIV_ROUND_UP(count, 0xffff);
>>
>> ...that produces the same result as the old loop, but am curious to
>> know why you chose the "count + 1" and "0x10000".
>>
>
> Hi Doug,
>
> I thought the idea was to keep (count / div) less than 0x10000, which you
> get
> by dividing through 0x10000. 0x10000 / 0x10000 = 1, though, so I added 1
> to the counter. But maybe I was thinking too much ;-).
Ah, I was trying to keep "DIV_ROUND_UP(count, divisor);" less than
0x10000, which (I think) means that you need to do division by 0xFFFF.
Specifically below in my patch I use DIV_ROUND_UP() since I want to
error on the side of having a higher count (fire later). This stuff
always makes my head spin, though.
I believe that DIV_ROUND_UP(0x1ffff, 2) = 0x10000, which is greater than 0xffff.
> Now, 0x1ffff / 2 = 0xffff is still lower than 0x10000, which is what
> I thought is the requirement. Ultimately the error is small either way,
> so DIV_ROUND_UP(count, 0xffff) is just as good to me to avoid the loop.
I did code up a quick test script that made sure that the result with
"DIV_ROUND_UP(count, 0xffff)" matched the results of the loop that I
coded up in the first version of this patchset for all reasonable
values of count, so I'm going to go with that.
Spun patch coming right up...
-Doug
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v2] watchdog: s3c2410_wdt: Handle rounding a little better for timeout
2013-11-27 0:57 ` [PATCH v2] " Doug Anderson
@ 2013-11-27 1:04 ` Guenter Roeck
2014-01-08 20:03 ` Wim Van Sebroeck
1 sibling, 0 replies; 8+ messages in thread
From: Guenter Roeck @ 2013-11-27 1:04 UTC (permalink / raw)
To: Doug Anderson, Wim Van Sebroeck
Cc: Leela Krishna Amudala, Olof Johansson, Tomasz Figa, Kukjin Kim,
Ben Dooks, linux-arm-kernel, linux-samsung-soc, linux-watchdog,
linux-kernel
On 11/26/2013 04:57 PM, Doug Anderson wrote:
> 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.
>
> At the same time we can avoid a for loop by just doing the right math.
>
> Signed-off-by: Doug Anderson <dianders@chromium.org>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
> ---
> Changes in v2:
> - Avoid a for loop as per Guenter.
>
> drivers/watchdog/s3c2410_wdt.c | 13 +++++--------
> 1 file changed, 5 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/watchdog/s3c2410_wdt.c b/drivers/watchdog/s3c2410_wdt.c
> index 7d8fd04..d9bcd6e 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",
> @@ -200,21 +200,18 @@ static int s3c2410wdt_set_heartbeat(struct watchdog_device *wdd, unsigned timeou
> */
>
> if (count >= 0x10000) {
> - for (divisor = 1; divisor <= 0x100; divisor++) {
> - if ((count / divisor) < 0x10000)
> - break;
> - }
> + divisor = DIV_ROUND_UP(count, 0xffff);
>
> - 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 */
>
^ permalink raw reply [flat|nested] 8+ messages in thread
* Re: [PATCH v2] watchdog: s3c2410_wdt: Handle rounding a little better for timeout
2013-11-27 0:57 ` [PATCH v2] " Doug Anderson
2013-11-27 1:04 ` Guenter Roeck
@ 2014-01-08 20:03 ` Wim Van Sebroeck
1 sibling, 0 replies; 8+ messages in thread
From: Wim Van Sebroeck @ 2014-01-08 20:03 UTC (permalink / raw)
To: Doug Anderson
Cc: Guenter Roeck, Leela Krishna Amudala, Olof Johansson,
Tomasz Figa, Kukjin Kim, Ben Dooks, linux-arm-kernel,
linux-samsung-soc, linux-watchdog, linux-kernel
Hi Doug,
> 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.
>
> At the same time we can avoid a for loop by just doing the right math.
>
> Signed-off-by: Doug Anderson <dianders@chromium.org>
> ---
> Changes in v2:
> - Avoid a for loop as per Guenter.
Patch added to linux-watchdog-next.
Kind regards,
Wim.
^ permalink raw reply [flat|nested] 8+ messages in thread
end of thread, other threads:[~2014-01-08 20:04 UTC | newest]
Thread overview: 8+ messages (download: mbox.gz / follow: Atom feed)
-- links below jump to the message on this page --
2013-11-26 18:30 [PATCH] watchdog: s3c2410_wdt: Handle rounding a little better for timeout Doug Anderson
2013-11-26 18:48 ` Guenter Roeck
2013-11-26 21:34 ` Doug Anderson
2013-11-27 0:10 ` Guenter Roeck
2013-11-27 0:57 ` Doug Anderson
2013-11-27 0:57 ` [PATCH v2] " Doug Anderson
2013-11-27 1:04 ` Guenter Roeck
2014-01-08 20:03 ` Wim Van Sebroeck
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