RE: [PATCH] soundwire: master: use pm_runtime_set_active() on add

["Liao, Bard" <bard.liao@intel.com>]

> -----Original Message-----
> From: Vinod Koul <vkoul@kernel.org>
> Sent: Wednesday, November 25, 2020 1:05 PM
> To: Bard Liao <yung-chuan.liao@linux.intel.com>
> Cc: alsa-devel@alsa-project.org; linux-kernel@vger.kernel.org;
> gregkh@linuxfoundation.org; jank@cadence.com;
> srinivas.kandagatla@linaro.org; rander.wang@linux.intel.com;
> ranjani.sridharan@linux.intel.com; hui.wang@canonical.com; pierre-
> louis.bossart@linux.intel.com; Kale, Sanyog R <sanyog.r.kale@intel.com>; Lin,
> Mengdong <mengdong.lin@intel.com>; Liao, Bard <bard.liao@intel.com>
> Subject: Re: [PATCH] soundwire: master: use pm_runtime_set_active() on
> add
> 
> On 24-11-20, 21:07, Bard Liao wrote:
> > From: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
> >
> > The 'master' device acts as a glue layer used during bus
> > initialization only, and it needs to be 'transparent' for pm_runtime
> > management. Its behavior should be that it becomes active when one of
> > its children becomes active, and suspends when all of its children are
> > suspended.
> >
> > In our tests on Intel platforms, we routinely see these sort of
> > warnings on the initial boot:
> >
> > [ 21.447345] rt715 sdw:3:25d:715:0: runtime PM trying to activate
> > child device sdw:3:25d:715:0 but parent (sdw-master-3) is not active
> >
> > This is root-caused to a missing setup to make the device 'active' on
> > probe. Since we don't want the device to remain active forever after
> > the probe, the autosuspend configuration is also enabled at the end of
> > the probe - the device will actually autosuspend only in the case
> > where there are no devices physically attached. In practice, the
> > master device will suspend when all its children are no longer active.
> >
> > Fixes: bd84256e86ecf ('soundwire: master: enable pm runtime')
> > Signed-off-by: Pierre-Louis Bossart
> > <pierre-louis.bossart@linux.intel.com>
> > Reviewed-by: Rander Wang <rander.wang@linux.intel.com>
> > Signed-off-by: Bard Liao <yung-chuan.liao@linux.intel.com>
> > ---
> >  drivers/soundwire/master.c | 14 ++++++++++++++
> >  1 file changed, 14 insertions(+)
> >
> > diff --git a/drivers/soundwire/master.c b/drivers/soundwire/master.c
> > index 3488bb824e84..9b05c9e25ebe 100644
> > --- a/drivers/soundwire/master.c
> > +++ b/drivers/soundwire/master.c
> > @@ -8,6 +8,15 @@
> >  #include <linux/soundwire/sdw_type.h>  #include "bus.h"
> >
> > +/*
> > + * The 3s value for autosuspend will only be used if there are no
> > + * devices physically attached on a bus segment. In practice enabling
> > + * the bus operation will result in children devices become active
> > +and
> > + * the master device will only suspend when all its children are no
> > + * longer active.
> > + */
> > +#define SDW_MASTER_SUSPEND_DELAY_MS 3000
> > +
> >  /*
> >   * The sysfs for properties reflects the MIPI description as given
> >   * in the MIPI DisCo spec
> > @@ -154,7 +163,12 @@ int sdw_master_device_add(struct sdw_bus *bus,
> struct device *parent,
> >  	bus->dev = &md->dev;
> >  	bus->md = md;
> >
> > +	pm_runtime_set_autosuspend_delay(&bus->md->dev,
> SDW_MASTER_SUSPEND_DELAY_MS);
> > +	pm_runtime_use_autosuspend(&bus->md->dev);
> > +	pm_runtime_mark_last_busy(&bus->md->dev);
> > +	pm_runtime_set_active(&bus->md->dev);
> >  	pm_runtime_enable(&bus->md->dev);
> > +	pm_runtime_idle(&bus->md->dev);
> 
> I understand that this needs to be done somewhere but is the core the right
> place. In intel case it maybe a dummy device but other controllers are real
> devices and may not support pm.
> 
> I think better idea would be to do this in respective driver.. that way it
> would be an opt-in for device supporting pm.

Should it be put in the same place as pm_runtime_enable?
IMHO, pm_runtime_enable is in the core already and it seems to be harmless
for devices which don't support pm. And pm can still be optional on md's
parent device.


> 
> Thanks
> --
> ~Vinod