From: Neil Armstrong <narmstrong@baylibre.com>
To: "Martin Blumenstingl" <martin.blumenstingl@googlemail.com>,
"Uwe Kleine-König" <u.kleine-koenig@pengutronix.de>
Cc: thierry.reding@gmail.com, jbrunet@baylibre.com,
linux-pwm@vger.kernel.org, linux-amlogic@lists.infradead.org,
linux-arm-kernel@lists.infradead.org,
linux-kernel@vger.kernel.org, kernel@pengutronix.de
Subject: Re: [PATCH 0/1] pwm: meson: fix scheduling while atomic issue
Date: Mon, 1 Apr 2019 09:25:40 +0200 [thread overview]
Message-ID: <1e6f9589-ff9a-f0fd-f12d-d680ffd58752@baylibre.com> (raw)
In-Reply-To: <CAFBinCCGWsb+1WHFe6uwrpUYgH4iix0WT8_v_Nj5BhGKRyjiLQ@mail.gmail.com>
On 30/03/2019 20:29, Martin Blumenstingl wrote:
> Hello Uwe,
>
> On Mon, Mar 25, 2019 at 9:07 PM Uwe Kleine-König
> <u.kleine-koenig@pengutronix.de> wrote:
> [...]
>>>> - Does stopping the PWM (i.e. clearing MISC_{A,B}_EN in the MISC_AB
>>>> register) freeze the output, or is the currently running period
>>>> completed first? (The latter is the right behaviour.)
>>> I don't know, I would have to measure this with a logic analyzer.
>>
>> In practise you can do this with a multimeter, too. Just do something
>> like:
>>
>> pwm_apply_state({ .enabled = true, .period = 5s, .duty_cycle = 5s, .polarity = PWM_POLARITY_NORMAL });
>> pwm_apply_state({ .enabled = false, .period = 5s, .duty_cycle = 5s, .polarity = PWM_POLARITY_NORMAL });
>>
>> (assuming the PWM supports periods that long). The expectation is that
>> the last command takes nearly 5 s to complete and while it waits the
>> output is high and on return it's low. If that isn't the case, there is
>> a bug somewhere.
> the longest supported period (using the 24MHz crystal as input, which
> is the slowest input clock and thus gives the longest possible
> duration) is 349514407ns (that's approx. 0.35 seconds). my multimeter
> isn't fast enough to measure this so I'm using my logic analyzer with
> puleseview instead: [0]
>
> I added the following code to meson_pwm_request:
> struct pwm_state enable = {
> .enabled = true,
> .period = 349514407U,
> .duty_cycle = 349514407U,
> .polarity = PWM_POLARITY_NORMAL };
> struct pwm_state disable = {
> .enabled = false,
> .period = 349514407U,
> .duty_cycle = 349514407U,
> .polarity = PWM_POLARITY_NORMAL };
> pwm_apply_state(pwm, &enable);
> pwm_apply_state(pwm, &disable);
>
> this returns immediately. my logic analyzer doesn't see signal change
> (I'm sampling at 1MHz).
>
> can you please confirm that my test code and measurement procedure is correct?
> if it is then my observation is that disabling the PWM does so
> immediately, without waiting for the current period to complete
I'm pretty 100,00000000000000% sure the HW doesn't permit waiting for a period to finish.
For disable states, we can either play on the period (high period at 0xffff for disable
at PWM_POLARITY_INVERSED and high period at 0 for PWM_POLARITY_NORMAL, if the HW behaves
correctly) or by adding some pinctrl states switching to GPIO modes and adding the
enable output high and output low property.
Neil
>
>
> Regards
> Martin
>
>
> [0] https://sigrok.org/wiki/Lcsoft_Mini_Board
>
next prev parent reply other threads:[~2019-04-01 7:25 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-24 22:02 [PATCH 0/1] pwm: meson: fix scheduling while atomic issue Martin Blumenstingl
2019-03-24 22:02 ` [PATCH 1/1] pwm: meson: use the spin-lock only to protect register modifications Martin Blumenstingl
2019-03-25 8:48 ` Uwe Kleine-König
2019-03-25 8:41 ` [PATCH 0/1] pwm: meson: fix scheduling while atomic issue Uwe Kleine-König
2019-03-25 8:50 ` Uwe Kleine-König
2019-03-25 17:41 ` Martin Blumenstingl
2019-03-25 20:07 ` Uwe Kleine-König
2019-03-26 20:05 ` Martin Blumenstingl
2019-03-30 19:29 ` Martin Blumenstingl
2019-03-31 18:47 ` Uwe Kleine-König
2019-04-01 7:25 ` Neil Armstrong [this message]
2019-03-26 9:06 ` Neil Armstrong
2019-03-26 10:54 ` Uwe Kleine-König
2019-03-25 9:35 ` Jerome Brunet
2019-03-25 18:04 ` Martin Blumenstingl
2019-03-26 8:37 ` Jerome Brunet
2019-03-26 8:57 ` Neil Armstrong
2019-03-26 20:16 ` Martin Blumenstingl
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