On Mon, Jun 22, 2020 at 08:39:43PM -0400, Sasha Levin wrote:
> On Fri, Jun 19, 2020 at 03:45:07PM +0200, gregkh@xxxxxxxxxxxxxxxxxxx wrote:
> >
> > The patch below does not apply to the 5.4-stable tree.
> > If someone wants it applied there, or to any other stable or longterm
> > tree, then please email the backport, including the original git commit
> > id to <stable@xxxxxxxxxxxxxxx>.
See below for a backport.
> > thanks,
> >
> > greg k-h
> >
> > ------------------ original commit in Linus's tree ------------------
> >
> > From 9017dc4fbd59c09463019ce494cfe36d654495a8 Mon Sep 17 00:00:00 2001
> > From: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> > Date: Wed, 27 May 2020 13:52:23 +0200
> > Subject: [PATCH] pwm: jz4740: Enhance precision in calculation of duty cycle
> > MIME-Version: 1.0
> > Content-Type: text/plain; charset=UTF-8
> > Content-Transfer-Encoding: 8bit
> >
> > Calculating the hardware value for the duty from the hardware value of
> > the period resulted in a precision loss versus calculating it from the
> > clock rate directly.
> >
> > (Also remove a cast that doesn't really need to be here)
> >
> > Fixes: f6b8a5700057 ("pwm: Add Ingenic JZ4740 support")
> > Cc: <stable@xxxxxxxxxxxxxxx>
> > Suggested-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> > Reviewed-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
> > Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> > Signed-off-by: Thierry Reding <thierry.reding@xxxxxxxxx>
>
> I suspect that the fixes tag should have been pointing to ce1f9cece057
> ("pwm: jz4740: Use clocks from TCU driver") instead.
No, f6b8a5700057 is right. The cast that was dropped isn't there, but
the suboptimal calculation is.
The backport on top of 5.4.y looks as follows:
From b39d3d4c6ba4b7ba8b97a0f7e650924920e4d95c Mon Sep 17 00:00:00 2001
From: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
Date: Wed, 27 May 2020 13:52:23 +0200
Subject: [PATCH] pwm: jz4740: Enhance precision in calculation of duty cycle
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
commit 9017dc4fbd59c09463019ce494cfe36d654495a8 upstream.
Calculating the hardware value for the duty from the hardware value of
the period resulted in a precision loss versus calculating it from the
clock rate directly.
Fixes: f6b8a5700057 ("pwm: Add Ingenic JZ4740 support")
Cc: <stable@xxxxxxxxxxxxxxx>
Suggested-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Reviewed-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
Signed-off-by: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
Signed-off-by: Thierry Reding <thierry.reding@xxxxxxxxx>
[ukl: backport to v5.4.y and adapt commit log accordingly]
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@xxxxxxxxxxxxxx>
---
drivers/pwm/pwm-jz4740.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/drivers/pwm/pwm-jz4740.c b/drivers/pwm/pwm-jz4740.c
index 9d78cc21cb12..d0f5c69930d0 100644
--- a/drivers/pwm/pwm-jz4740.c
+++ b/drivers/pwm/pwm-jz4740.c
@@ -108,8 +108,8 @@ static int jz4740_pwm_apply(struct pwm_chip *chip, struct pwm_device *pwm,
if (prescaler == 6)
return -EINVAL;
- tmp = (unsigned long long)period * state->duty_cycle;
- do_div(tmp, state->period);
+ tmp = (unsigned long long)rate * state->duty_cycle;
+ do_div(tmp, NSEC_PER_SEC);
duty = period - tmp;
if (duty >= period)
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
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