linux-kernel - Re: [PATCH v7 3/5] remoteproc: Add support for runtime PM

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Message-ID: <20200611043951.GA3251@builder.lan>
Date:   Wed, 10 Jun 2020 21:39:51 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Paul Cercueil <paul@...pouillou.net>
Cc:     Suman Anna <s-anna@...com>, Ohad Ben-Cohen <ohad@...ery.com>,
        Arnaud Pouliquen <arnaud.pouliquen@...com>,
        Loic Pallardy <loic.pallardy@...com>, od@...c.me,
        linux-remoteproc@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, Tero Kristo <t-kristo@...com>
Subject: Re: [PATCH v7 3/5] remoteproc: Add support for runtime PM

On Wed 10 Jun 02:40 PDT 2020, Paul Cercueil wrote:

> Hi,
> 
> Le lun. 8 juin 2020 à 18:10, Suman Anna <s-anna@...com> a écrit :
> > Hi Paul,
> > 
> > On 6/8/20 5:46 PM, Paul Cercueil wrote:
> > > Hi Suman,
> > > 
> > > > > > On 5/15/20 5:43 AM, Paul Cercueil wrote:
> > > > > > > Call pm_runtime_get_sync() before the firmware is loaded, and
> > > > > > > pm_runtime_put() after the remote processor has been stopped.
> > > > > > > 
> > > > > > > Even though the remoteproc device has no PM
> > > > > > > callbacks, this allows the
> > > > > > > parent device's PM callbacks to be properly called.
> > > > > > 
> > > > > > I see this patch staged now for 5.8, and the latest
> > > > > > -next branch has broken the pm-runtime autosuspend
> > > > > > feature we have in the OMAP remoteproc driver. See
> > > > > > commit 5f31b232c674 ("remoteproc/omap: Add support
> > > > > > for runtime auto-suspend/resume").
> > > > > > 
> > > > > > What was the original purpose of this patch, because
> > > > > > there can be differing backends across different
> > > > > > SoCs.
> > > > > 
> > > > > Did you try pm_suspend_ignore_children()? It looks like it
> > > > > was made for your use-case.
> > > > 
> > > > Sorry for the delay in getting back. So, using
> > > > pm_suspend_ignore_children() does fix my current issue.
> > > > 
> > > > But I still fail to see the original purpose of this patch in
> > > > the remoteproc core especially given that the core itself does
> > > > not have any callbacks. If the sole intention was to call the
> > > > parent pdev's callbacks, then I feel that state-machine is
> > > > better managed within that particular platform driver itself,
> > > > as the sequencing/device management can vary with different
> > > > platform drivers.
> > > 
> > > The problem is that with Ingenic SoCs some clocks must be enabled in
> > > order to load the firmware, and the core doesn't give you an option
> > > to register a callback to be called before loading it.
> > 
> > Yep, I have similar usage in one of my remoteproc drivers (see
> > keystone_remoteproc.c), and I think this all stems from the need to
> > use/support loading into a processor's internal memories. My driver does
> > leverage the pm-clks backend plugged into pm_runtime, so you won't see
> > explicit calls on the clocks.
> > 
> > I guess the question is what exact PM features you are looking for with
> > the Ingenic SoC. I do see you are using pm_runtime autosuspend, and your
> > callbacks are managing the clocks, but reset is managed only in
> > start/stop.
> > 
> > > The first version of my patchset added .prepare/.unprepare
> > > callbacks to the struct rproc_ops, but the feedback from the
> > > maintainers was that I should do it via runtime PM. However, it was
> > > not possible to keep it contained in the driver, since again the
> > > core doesn't provide a "prepare" callback, so no place to call
> > > pm_runtime_get_sync().
> > FWIW, the .prepare/.unprepare callbacks is actually now part of the
> > rproc core. Looks like multiple developers had a need for this, and this
> > functionality went in at the same time as your driver :). Not sure if
> > you looked up the prior patches, I leveraged the patch that Loic had
> > submitted a long-time ago, and a revised version of it is now part of
> > 5.8-rc1.
> 
> WTF maintainers, you refuse my patchset for adding a .prepare/.unprepare,
> ask me to do it via runtime PM, then merge another patchset that adds these
> callback. At least be constant in your decisions.
> 

Sorry, I missed this when applying the two patches, but you're of course
right.

> Anyway, now we have two methods added to linux-next for doing the exact same
> thing. What should we do about it?
> 

I like the pm_runtime approach and as it was Arnaud that asked you to
change it, perhaps he and Loic can agree on updating the ST driver so we
can drop the prepare/unprepare ops again?

Regards,
Bjorn