Re: [PATCH] dd: Invoke one probe retry cycle after every initcall level

[rishabhb]

On 2018-07-23 04:17, Rafael J. Wysocki wrote:
> On Thu, Jul 19, 2018 at 11:24 PM, Rishabh Bhatnagar
> <rishabhb@xxxxxxxxxxxxxx> wrote:
> > Drivers that are registered at an initcall level may have to
> > wait until late_init before the probe deferral mechanism can
> > retry their probe functions. It is possible that their
> > dependencies were resolved much earlier, in some cases even
> > before the next initcall level. Invoke one probe retry cycle
> > at every _sync initcall level, allowing these drivers to be
> > probed earlier.
>
> Can you please say something about the actual use case this is
> expected to address?
We have a display driver that depends 3 other devices to be
probed so that it can bring-up the display. Because of dependencies
not being met the deferral mechanism defers the probes for a later time,
even though the dependencies might be met earlier. With this change
display can be brought up much earlier.
> > Signed-off-by: Vikram Mulukutla <markivx@xxxxxxxxxxxxxx>
> > Signed-off-by: Rishabh Bhatnagar <rishabhb@xxxxxxxxxxxxxx>
> > ---
> >  drivers/base/dd.c | 33 +++++++++++++++++++++++++++------
> >  1 file changed, 27 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/base/dd.c b/drivers/base/dd.c
> > index 1435d72..e6a6821 100644
> > --- a/drivers/base/dd.c
> > +++ b/drivers/base/dd.c
> > @@ -224,23 +224,44 @@ void device_unblock_probing(void)
> >         driver_deferred_probe_trigger();
> >  }
> >
> > +static void enable_trigger_defer_cycle(void)
> > +{
> > +       driver_deferred_probe_enable = true;
> > +       driver_deferred_probe_trigger();
> > +       /*
> > +        * Sort as many dependencies as possible before the next 
> > initcall
> > +        * level
> > +        */
> > +       flush_work(&deferred_probe_work);
> > +}
> > +
> >  /**
> >   * deferred_probe_initcall() - Enable probing of deferred devices
> >   *
> >   * We don't want to get in the way when the bulk of drivers are 
> > getting probed.
> >   * Instead, this initcall makes sure that deferred probing is delayed 
> > until
> > - * late_initcall time.
> > + * all the registered initcall functions at a particular level are 
> > completed.
> > + * This function is invoked at every *_initcall_sync level.
> >   */
> >  static int deferred_probe_initcall(void)
> >  {
> > -       driver_deferred_probe_enable = true;
> > -       driver_deferred_probe_trigger();
> > -       /* Sort as many dependencies as possible before exiting 
> > initcalls */
> > -       flush_work(&deferred_probe_work);
> > +       enable_trigger_defer_cycle();
> > +       driver_deferred_probe_enable = false;
> > +       return 0;
> > +}
> > +arch_initcall_sync(deferred_probe_initcall);
> > +subsys_initcall_sync(deferred_probe_initcall);
> > +fs_initcall_sync(deferred_probe_initcall);
> > +device_initcall_sync(deferred_probe_initcall);
> > +
> > +static int deferred_probe_enable_fn(void)
> > +{
> > +       /* Enable deferred probing for all time */
> > +       enable_trigger_defer_cycle();
> >         initcalls_done = true;
> >         return 0;
> >  }
> > -late_initcall(deferred_probe_initcall);
> > +late_initcall(deferred_probe_enable_fn);
> >
> >  /**
> >   * device_is_bound() - Check if device is bound to a driver
> > --
> > The Qualcomm Innovation Center, Inc. is a member of the Code Aurora 
> > Forum,
> > a Linux Foundation Collaborative Project