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Date:   Thu, 28 May 2020 02:01:38 +0000
From:   Anson Huang <anson.huang@....com>
To:     Marc Kleine-Budde <mkl@...gutronix.de>,
        "jassisinghbrar@...il.com" <jassisinghbrar@...il.com>,
        "shawnguo@...nel.org" <shawnguo@...nel.org>,
        "s.hauer@...gutronix.de" <s.hauer@...gutronix.de>,
        "kernel@...gutronix.de" <kernel@...gutronix.de>,
        "festevam@...il.com" <festevam@...il.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>
CC:     dl-linux-imx <linux-imx@....com>
Subject: RE: [PATCH] mailbox: imx: Support runtime PM

Gentle ping...


> Subject: RE: [PATCH] mailbox: imx: Support runtime PM
> 
> Hi, Marc
> 
> > Subject: Re: [PATCH] mailbox: imx: Support runtime PM
> >
> > On 4/13/20 2:25 PM, Anson Huang wrote:
> > > Some power hungry sub-systems like VPU has its own MUs which also
> > > use mailbox driver, current mailbox driver uses platform driver
> > > model and MU's power will be ON after driver probed and left ON
> > > there, it may cause the whole sub-system can NOT enter lower power
> > > mode, take VPU driver for example, it has runtime PM support, but
> > > due to its MU always ON, the VPU sub-system will be always ON and
> > > consume many power during kernel idle.
> > >
> > > To save power in kernel idle, mailbox driver needs to support
> > > runtime PM in order to power off MU when it is unused. However, the
> > > runtime suspend/resume can ONLY be implemented in mailbox's
> > > .shutdown/.startup callback, so its consumer needs to call
> > > mbox_request_channel()/mbox_free_channel() in consumer driver's
> > > runtime PM callback, then the MU's power will be ON/OFF along with
> > > consumer's runtime PM status.
> > >
> > > Signed-off-by: Anson Huang <Anson.Huang@....com>
> > > ---
> > >  drivers/mailbox/imx-mailbox.c | 27 ++++++++++++++++++++++++++-
> > >  1 file changed, 26 insertions(+), 1 deletion(-)
> > >
> > > diff --git a/drivers/mailbox/imx-mailbox.c
> > > b/drivers/mailbox/imx-mailbox.c index 7906624..97bf0ac 100644
> > > --- a/drivers/mailbox/imx-mailbox.c
> > > +++ b/drivers/mailbox/imx-mailbox.c
> > > @@ -12,6 +12,7 @@
> > >  #include <linux/mailbox_controller.h>  #include <linux/module.h>
> > > #include <linux/of_device.h>
> > > +#include <linux/pm_runtime.h>
> > >  #include <linux/slab.h>
> > >
> > >  #define IMX_MU_xSR_GIPn(x)	BIT(28 + (3 - (x)))
> > > @@ -287,6 +288,7 @@ static int imx_mu_startup(struct mbox_chan
> *chan)
> > >  	struct imx_mu_con_priv *cp = chan->con_priv;
> > >  	int ret;
> > >
> > > +	pm_runtime_get_sync(priv->dev);
> > >  	if (cp->type == IMX_MU_TYPE_TXDB) {
> > >  		/* Tx doorbell don't have ACK support */
> > >  		tasklet_init(&cp->txdb_tasklet, imx_mu_txdb_tasklet, @@
> -323,6
> > > +325,7 @@ static void imx_mu_shutdown(struct mbox_chan *chan)
> > >
> > >  	if (cp->type == IMX_MU_TYPE_TXDB) {
> > >  		tasklet_kill(&cp->txdb_tasklet);
> > > +		pm_runtime_put_sync(priv->dev);
> > >  		return;
> > >  	}
> > >
> > > @@ -341,6 +344,7 @@ static void imx_mu_shutdown(struct mbox_chan
> > *chan)
> > >  	}
> > >
> > >  	free_irq(priv->irq, chan);
> > > +	pm_runtime_put_sync(priv->dev);
> > >  }
> > >
> > >  static const struct mbox_chan_ops imx_mu_ops = { @@ -508,7 +512,27
> > @@
> > > static int imx_mu_probe(struct platform_device *pdev)
> > >
> > >  	platform_set_drvdata(pdev, priv);
> > >
> > > -	return devm_mbox_controller_register(dev, &priv->mbox);
> > > +	ret = devm_mbox_controller_register(dev, &priv->mbox);
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	pm_runtime_enable(dev);
> > > +
> >
> > First registering at the system and then setting up the power
> > management looks racy. Don't know if this is serialized by some other
> means.
> 
> Don't have other means, just refer to
> drivers/mailbox/omap-mailbox.c, it has same sequence, NOT sure if there is
> special requirement about this sequence.
> 
> Thanks,
> Anson

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