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>, Vignesh R <vigneshr@ti.com>
Subject: Re: [PATCH v3 4/5] pwm: omap-dmtimer: Do not disable pwm before changing period/duty_cycle
Date: Thu, 12 Mar 2020 07:40:42 +0100 [thread overview]
Message-ID: <20200312064042.p7himm3odxjyzroi@pengutronix.de> (raw)
In-Reply-To: <20200312042210.17344-5-lokeshvutla@ti.com>
On Thu, Mar 12, 2020 at 09:52:09AM +0530, Lokesh Vutla wrote:
> Only the Timer control register(TCLR) cannot be updated when the timer
> is running. 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.
I'm not sure what is sensible here. Stopping the PWM for a short period
is bad, but maybe emitting a wrong period isn't better. You can however
optimise it if only one of period or duty_cycle changes.
@Thierry, what is your position here? I tend to say a short stop is
preferable.
> Tested-by: Tony Lindgren <tony@atomide.com>
> Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
> ---
> drivers/pwm/pwm-omap-dmtimer.c | 21 +++++++--------------
> 1 file changed, 7 insertions(+), 14 deletions(-)
>
> diff --git a/drivers/pwm/pwm-omap-dmtimer.c b/drivers/pwm/pwm-omap-dmtimer.c
> index 85b17b49980b..c56e7256e923 100644
> --- a/drivers/pwm/pwm-omap-dmtimer.c
> +++ b/drivers/pwm/pwm-omap-dmtimer.c
> @@ -19,6 +19,13 @@
> * Limitations:
> * - When PWM is stopped, timer counter gets stopped immediately. This
> * doesn't allow the current PWM period to complete and stops abruptly.
> + * - When PWM is running and changing both duty cycle and period,
> + * we cannot prevent in software that the output might produce
> + * a period with mixed settings. Especially when period/duty_cyle
> + * is updated while the pwm pin is high, current pwm period/duty_cycle
> + * can get updated as below based on the current timer counter:
> + * - period for current cycle = current_period + new period
> + * - duty_cycle for current period = current period + new duty_cycle.
In case we stay with a short stop, adding something like:
- The PWM has to be stopped for updates of both period and duty_cycle.
Best regards
Uwe
--
Pengutronix e.K. | Uwe Kleine-König |
Industrial Linux Solutions | https://www.pengutronix.de/ |
next prev parent reply other threads:[~2020-03-12 6:40 UTC|newest]
Thread overview: 48+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-03-12 4:22 [PATCH v3 0/5] pwm: omap-dmtimer: Allow for dynamic pwm period updates Lokesh Vutla
2020-03-12 4:22 ` Lokesh Vutla
2020-03-12 4:22 ` [PATCH v3 1/5] pwm: omap-dmtimer: Drop unused header file Lokesh Vutla
2020-03-12 4:22 ` Lokesh Vutla
2020-03-12 6:35 ` Uwe Kleine-König
2020-03-12 4:22 ` [PATCH v3 2/5] pwm: omap-dmtimer: Update description for pwm omap dm timer Lokesh Vutla
2020-03-12 4:22 ` Lokesh Vutla
2020-03-12 6:35 ` Uwe Kleine-König
2020-03-12 4:22 ` [PATCH v3 3/5] pwm: omap-dmtimer: Fix pwm enabling sequence Lokesh Vutla
2020-03-12 4:22 ` Lokesh Vutla
2020-03-12 4:22 ` [PATCH v3 4/5] pwm: omap-dmtimer: Do not disable pwm before changing period/duty_cycle Lokesh Vutla
2020-03-12 4:22 ` Lokesh Vutla
2020-03-12 6:40 ` Uwe Kleine-König [this message]
2020-03-12 8:05 ` Lokesh Vutla
2020-03-12 8:05 ` Lokesh Vutla
2020-03-12 8:47 ` Uwe Kleine-König
2020-03-12 10:44 ` Lokesh Vutla
2020-03-12 10:44 ` Lokesh Vutla
2020-03-12 14:21 ` Richard Cochran
2020-03-12 17:14 ` Lokesh Vutla
2020-03-18 4:40 ` Lokesh Vutla
2020-03-18 4:40 ` Lokesh Vutla
2020-03-30 14:14 ` Thierry Reding
2020-03-30 19:16 ` Uwe Kleine-König
2020-03-31 20:45 ` Thierry Reding
2020-04-01 8:22 ` Uwe Kleine-König
2020-04-01 10:22 ` Lokesh Vutla
2020-04-01 10:22 ` Lokesh Vutla
2020-04-01 11:47 ` Uwe Kleine-König
2020-04-01 18:39 ` Thierry Reding
2020-04-01 20:36 ` Uwe Kleine-König
2020-04-01 18:28 ` Thierry Reding
2020-04-01 20:31 ` Uwe Kleine-König
2020-04-01 21:37 ` Thierry Reding
2020-04-02 14:02 ` Uwe Kleine-König
2020-04-03 8:51 ` Lokesh Vutla
2020-04-03 8:51 ` Lokesh Vutla
2020-04-03 13:59 ` Uwe Kleine-König
2020-03-31 15:29 ` Lokesh Vutla
2020-03-31 15:29 ` Lokesh Vutla
2020-03-31 20:10 ` Thierry Reding
2020-04-01 10:15 ` Lokesh Vutla
2020-03-12 4:22 ` [PATCH v3 5/5] pwm: omap-dmtimer: Implement .apply callback Lokesh Vutla
2020-03-12 4:22 ` Lokesh Vutla
2020-03-13 15:31 ` Tony Lindgren
2020-03-23 11:30 ` [PATCH v3 0/5] pwm: omap-dmtimer: Allow for dynamic pwm period updates Lokesh Vutla
2020-03-23 11:30 ` Lokesh Vutla
2020-03-30 14:04 ` Thierry Reding
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