linux-kernel - Re: [PATCH v2 4/6] pwm: omap-dmtimer: Fix pwm disabling sequence

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Message-ID: <20200313155049.GE37466@atomide.com>
Date:   Fri, 13 Mar 2020 08:50:49 -0700
From:   Tony Lindgren <tony@...mide.com>
To:     Lokesh Vutla <lokeshvutla@...com>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Uwe Kleine-König 
        <u.kleine-koenig@...gutronix.de>,
        Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
        linux-kernel@...r.kernel.org, linux-pwm@...r.kernel.org,
        Sekhar Nori <nsekhar@...com>, Vignesh R <vigneshr@...com>,
        Sebastian Reichel <sre@...nel.org>
Subject: Re: [PATCH v2 4/6] pwm: omap-dmtimer: Fix pwm disabling sequence

* Tony Lindgren <tony@...mide.com> [200313 15:35]:
> * Tony Lindgren <tony@...mide.com> [200312 00:59]:
> > * Lokesh Vutla <lokeshvutla@...com> [200311 04:14]:
> > > However, I see an issue with the patch itself as pm_runtime is not disabled
> > > after the pwm is stopped. Not sure how that could be nullified with this approach.
> > 
> > Hmm yeah not sure what could be used to clear things
> > when the current cycle is completed unless there's
> > some interrupt for it.
> 
> You could enable pm_runtime_use_autosuspend() for pwm use,
> then set the timeout to the cycle length, then in the
> runtime_suspend make sure the enable bit is cleared if
> requested.
> 
> But this too seems inaccurate, it would be best to clear
> the enable bit on some cycle completion interrupt if
> such thing is available.

I think enabling pm_runtime_use_autosuspend() for pwm,
adding a flag for pwm_enabled, and blocking cpu_pm if
pwm_enabled is set might do the trick though. Then clear
pwm_enabled flag in runtime_suspend if set.

This depend on cpuidle respecting NOTIFY_BAD that I
fixed in the recent thread:

[PATCH 0/3] Block idle in gpio-omap with cpu_pm

Regards,

Tony