linux-kernel - Re: [RFC PATCH v2 1/2] PM / domains: Introduce multi PM domains helpers

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Message-ID: <CAEnQRZDX8PZ7V+c8zfoxK-+oGp2pt8N3oTAC6=Ps1W33LGY7WA@mail.gmail.com>
Date:   Tue, 21 Apr 2020 17:18:45 +0300
From:   Daniel Baluta <daniel.baluta@...il.com>
To:     Ulf Hansson <ulf.hansson@...aro.org>
Cc:     Daniel Baluta <daniel.baluta@....nxp.com>,
        Aisheng Dong <aisheng.dong@....com>,
        Len Brown <len.brown@...el.com>,
        Linux-ALSA <alsa-devel@...a-project.org>,
        Linux PM <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        Kevin Hilman <khilman@...nel.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Ranjani Sridharan <ranjani.sridharan@...ux.intel.com>,
        Daniel Baluta <daniel.baluta@....com>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Paul Olaru <paul.olaru@....com>,
        dl-linux-imx <linux-imx@....com>,
        Sascha Hauer <kernel@...gutronix.de>,
        Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Fabio Estevam <festevam@...il.com>,
        "S.j. Wang" <shengjiu.wang@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Anson Huang <anson.huang@....com>
Subject: Re: [RFC PATCH v2 1/2] PM / domains: Introduce multi PM domains helpers

On Tue, Apr 21, 2020 at 5:01 PM Ulf Hansson <ulf.hansson@...aro.org> wrote:
>
> On Wed, 4 Mar 2020 at 13:20, Daniel Baluta <daniel.baluta@....nxp.com> wrote:
> >
> > From: Daniel Baluta <daniel.baluta@....com>
> >
> > This patch introduces helpers support for multi PM domains.
> >
> > API consists of:
> >
> > 1) dev_multi_pm_attach - powers up all PM domains associated with a given
> > device. Because we can attach one PM domain per device, we create
> > virtual devices (children of initial device) and associate PM domains
> > one per virtual device.
> >
> > 2) dev_multi_pm_detach - detaches all virtual devices from PM domains
> > attached with.
> >
> > Signed-off-by: Daniel Baluta <daniel.baluta@....com>
>
> First, apologize for the delay.
>
> In general I don't mind adding helpers that can be used to decrease
> open coding. However, in this case, I wonder how useful the helpers
> would really be.
>
> More precisely, according to the information I have, a device may not
> always need all of its PM domains to be turned on together, but
> perhaps only a subset of them. Depending on the current use case that
> is running.
>
> Of course, some cases follow your expectations, but as stated, some
> others do not.
>
> Do you have an idea how many users that would be able to switch to
> these new APIs as of today?

IMX Sound Open Firmware driver will immediately be available
to use this new API.

https://elixir.bootlin.com/linux/latest/source/sound/soc/sof/imx/imx8.c#L221

Aside, from that there are the ACM clock modules for i.MX8QXP / i.MX8QM. Also,
looking at our internal tree there are XUVI, VPU, DPU drivers that need multi
power domain support.

Anson, Aisheng do you have a number of users on your side for
multi power domain?

thanks,
daniel.