RE: [PATCH] mailbox: imx: Support runtime PM

[Anson Huang <anson.huang@nxp.com>]

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@nxp.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