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

[rishabhb]

On 2018-07-24 01:24, Rafael J. Wysocki wrote:
> On Mon, Jul 23, 2018 at 10:22 PM,  <rishabhb@xxxxxxxxxxxxxx> wrote:
> > 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.
>
> OK
>
> What runlevel brings up the display after the change?
>
> Thanks,
> Rafael
After the change the display can come up after device_initcall level
itself.
The above mentioned 3 devices are probed at 0.503253, 0.505210 and 
0.523264 secs.
Only the first device is probed successfully. With the current
deferral mechanism the devices get probed again after late_initcall
at 9.19 and 9.35 secs. So display can only come up after 9.35 secs.
With this change the devices are re-probed successfully at 0.60 and
0.613 secs. Therefore display can come just after 0.613 secs.
This change helps in overall android bootup as well.

-Rishabh