On Tue, 2018-04-03 at 12:29 +0200, Marcel Holtmann wrote:
> Hi Sean,
>
> > In order to open up the required power gate before any operation can be
> > effectively performed over the serial bus between CPU and serdev, it's
> > clearly essential to add common attach functions for PM domains to serdev
> > at the probe phase.
> >
> > Similarly, the relevant dettach function for the PM domains should be
> > properly and reversely added at the remove phase.
> >
> > Signed-off-by: Sean Wang <sean.wang@xxxxxxxxxxxx>
> > Cc: Rob Herring <robh@xxxxxxxxxx>
> > Cc: Ulf Hansson <ulf.hansson@xxxxxxxxxx>
> > Cc: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>
> > Cc: Jiri Slaby <jslaby@xxxxxxxx>
> > Cc: linux-serial@xxxxxxxxxxxxxxx
> > ---
> > drivers/tty/serdev/core.c | 14 +++++++++++++-
> > 1 file changed, 13 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/tty/serdev/core.c b/drivers/tty/serdev/core.c
> > index df93b72..c93d8ee 100644
> > --- a/drivers/tty/serdev/core.c
> > +++ b/drivers/tty/serdev/core.c
> > @@ -13,6 +13,7 @@
> > #include <linux/module.h>
> > #include <linux/of.h>
> > #include <linux/of_device.h>
> > +#include <linux/pm_domain.h>
> > #include <linux/serdev.h>
> > #include <linux/slab.h>
> >
> > @@ -330,8 +331,16 @@ EXPORT_SYMBOL_GPL(serdev_device_set_tiocm);
> > static int serdev_drv_probe(struct device *dev)
> > {
> > const struct serdev_device_driver *sdrv = to_serdev_device_driver(dev->driver);
> > + int ret;
> > +
> > + ret = dev_pm_domain_attach(dev, true);
> > + if (ret != -EPROBE_DEFER) {
> > + ret = sdrv->probe(to_serdev_device(dev));
> > + if (ret)
> > + dev_pm_domain_detach(dev, true);
> > + }
>
> so if this is deferred, when does the serdev device gets probed?
>
driver probe deferral mechanism is supported in driver core
deferred_probe_initcall makes sure that deferred probing is
delayed until late_initcall time.
Below is a few of word I got from drivers/base/core.c I thought it helps
to understand the mechanism in complete picture
* If a required resource is not available yet, a driver can
request probing to be deferred by returning -EPROBE_DEFER from
its probe hook.
* A driver returning -EPROBE_DEFER causes the device to be added to the
pending list. A successful driver probe will trigger moving all devices
from the pending to the active list so that the workqueue will
eventually retry them.
> >
> > - return sdrv->probe(to_serdev_device(dev));
> > + return ret;
> > }
> >
> > static int serdev_drv_remove(struct device *dev)
> > @@ -339,6 +348,9 @@ static int serdev_drv_remove(struct device *dev)
> > const struct serdev_device_driver *sdrv = to_serdev_device_driver(dev->driver);
> > if (sdrv->remove)
> > sdrv->remove(to_serdev_device(dev));
> > +
> > + dev_pm_domain_detach(dev, true);
> > +
> > return 0;
> > }
>
> Regards
>
> Marcel
>
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