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From: Thierry Reding <thierry.reding@gmail.com>
To: Mika Westerberg <mika.westerberg@linux.intel.com>
Cc: Dan O'Donovan <dan@emutex.com>, linux-pwm@vger.kernel.org
Subject: Re: [PATCH] pwm: lpss: Prevent on_time_div overflow on lower frequencies
Date: Fri, 10 Jun 2016 15:40:55 +0200	[thread overview]
Message-ID: <20160610134055.GJ27142@ulmo.ba.sec> (raw)
In-Reply-To: <1465562601-44876-1-git-send-email-mika.westerberg@linux.intel.com>

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On Fri, Jun 10, 2016 at 03:43:21PM +0300, Mika Westerberg wrote:
> If duty_ns is large enough multiplying it by 255 overflows and results
> wrong duty cycle value being programmed. For example with 10ms duty when
> period is 20ms (50%) we get
> 
>   255 * 10000000 / 20000000 = -87
> 
> because 255 * 10000000 overlows int. Whereas correct value should be
> 
>   255 * 10000000 / 20000000 = 127
> 
> Fix this by using unsigned long long as type for on_time_div and changing
> integer literals to use proper type annotation.
> 
> Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
> ---
> Resending with linux-pwm address corrected.
> 
> This is on top of Dan's patch:
> 
>   https://patchwork.ozlabs.org/patch/628683/
> 
>  drivers/pwm/pwm-lpss.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)

Applied, thanks.

Thierry

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      reply	other threads:[~2016-06-10 13:40 UTC|newest]

Thread overview: 2+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-06-10 12:43 [PATCH] pwm: lpss: Prevent on_time_div overflow on lower frequencies Mika Westerberg
2016-06-10 13:40 ` Thierry Reding [this message]

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