From: "Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
To: Lokesh Vutla <lokeshvutla@ti.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
Tony Lindgren <tony@atomide.com>,
Linux OMAP Mailing List <linux-omap@vger.kernel.org>,
linux-kernel@vger.kernel.org, linux-pwm@vger.kernel.org,
Sekhar Nori <nsekhar@ti.com>
Subject: Re: [PATCH 3/4] pwm: omap-dmtimer: Do not disable pwm before changing period/duty_cycle
Date: Tue, 25 Feb 2020 07:48:33 +0100 [thread overview]
Message-ID: <20200225064833.kmvaplfqqf53s3iy@pengutronix.de> (raw)
In-Reply-To: <4aedb6d4-1823-ab46-b7e6-cc0b30f7747d@ti.com>
Hello,
On Tue, Feb 25, 2020 at 10:32:42AM +0530, Lokesh Vutla wrote:
> On 24/02/20 2:25 PM, Uwe Kleine-König wrote:
> > Hello,
> >
> > On Mon, Feb 24, 2020 at 10:51:34AM +0530, Lokesh Vutla wrote:
> >> Only the Timer control register(TCLR) can be updated only when the timer
> >> is stopped. Registers like Counter register(TCRR), loader register(TLDR),
> >> match register(TMAR) can be updated when the counter is running. Since
> >> TCLR is not updated in pwm_omap_dmtimer_config(), do not stop the
> >> timer for period/duty_cycle update.
> >>
> >> Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
> >> ---
> >> drivers/pwm/pwm-omap-dmtimer.c | 14 --------------
> >> 1 file changed, 14 deletions(-)
> >>
> >> diff --git a/drivers/pwm/pwm-omap-dmtimer.c b/drivers/pwm/pwm-omap-dmtimer.c
> >> index f13be7216847..58c61559e72f 100644
> >> --- a/drivers/pwm/pwm-omap-dmtimer.c
> >> +++ b/drivers/pwm/pwm-omap-dmtimer.c
> >> @@ -102,7 +102,6 @@ static int pwm_omap_dmtimer_config(struct pwm_chip *chip,
> >> u32 load_value, match_value;
> >> struct clk *fclk;
> >> unsigned long clk_rate;
> >> - bool timer_active;
> >>
> >> dev_dbg(chip->dev, "requested duty cycle: %d ns, period: %d ns\n",
> >> duty_ns, period_ns);
> >> @@ -178,25 +177,12 @@ static int pwm_omap_dmtimer_config(struct pwm_chip *chip,
> >> load_value = (DM_TIMER_MAX - period_cycles) + 1;
> >> match_value = load_value + duty_cycles - 1;
> >>
> >> - /*
> >> - * We MUST stop the associated dual-mode timer before attempting to
> >> - * write its registers, but calls to omap_dm_timer_start/stop must
> >> - * be balanced so check if timer is active before calling timer_stop.
> >> - */
> >> - timer_active = pm_runtime_active(&omap->dm_timer_pdev->dev);
> >> - if (timer_active)
> >> - omap->pdata->stop(omap->dm_timer);
> >> -
> >> omap->pdata->set_load(omap->dm_timer, true, load_value);
> >> omap->pdata->set_match(omap->dm_timer, true, match_value);
> >
> > (Without having looked into the depths of the driver I assume
> > .set_load() sets the period of the PWM and .set_match() the duty cycle.)
>
> Right.
>
> >
> > What happens on a running PWM if you change the period? Consider you
> > change from duty_cycle = 1000, period = 5000 to duty_cycle = 4000,
> > period = 10000. As you set the period first, can it happen the hardware
> > produces a cycle with duty_cycle = 1000, period = 10000?
>
> No. So, the current cycle is un affected with duty_cycle = 1000 and period =
> 5000. Starting from next cycle new settings gets reflected with duty_cycle =
> 4000 and period = 10000.
Is the reference manual for this hardware publically available?
So the .set_load callback just writes a shadow register and .set_match
latches it into hardware atomically with its own register changes? A
comment in the source code about this would be good. Also if .set_load
doesn't work without .set_match I wonder if it is sane to put their
logic in two different functions.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
next prev parent reply other threads:[~2020-02-25 6:48 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-24 5:21 [PATCH 0/4] pwm: omap-dmtimer: Allow for dynamic pwm period updates Lokesh Vutla
2020-02-24 5:21 ` [PATCH 1/4] pwm: omap-dmtimer: Drop unused header file Lokesh Vutla
2020-02-24 7:53 ` Uwe Kleine-König
2020-02-25 5:02 ` Lokesh Vutla
2020-02-25 6:43 ` Uwe Kleine-König
2020-02-24 5:21 ` [PATCH 2/4] pwm: omap-dmtimer: Fix pwm enabling sequence Lokesh Vutla
2020-02-24 8:49 ` Uwe Kleine-König
2020-02-25 5:02 ` Lokesh Vutla
2020-02-24 5:21 ` [PATCH 3/4] pwm: omap-dmtimer: Do not disable pwm before changing period/duty_cycle Lokesh Vutla
2020-02-24 8:55 ` Uwe Kleine-König
2020-02-25 5:02 ` Lokesh Vutla
2020-02-25 6:48 ` Uwe Kleine-König [this message]
2020-02-25 7:59 ` Lokesh Vutla
2020-02-25 8:38 ` Uwe Kleine-König
2020-02-25 11:26 ` Lokesh Vutla
2020-02-26 16:35 ` Uwe Kleine-König
2020-02-24 5:21 ` [PATCH 4/4] pwm: omap-dmtimer: Implement .apply callback Lokesh Vutla
2020-02-24 9:07 ` Uwe Kleine-König
2020-02-25 5:01 ` Lokesh Vutla
2020-02-26 16:21 ` Uwe Kleine-König
2020-02-26 17:57 ` [PATCH 0/4] pwm: omap-dmtimer: Allow for dynamic pwm period updates Tony Lindgren
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