linux-kernel - Re: [PATCH] drivers: core: Clarify EPROBE

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Message-ID: <CABCoZhDb4u=Gj=CPrjH+6tS+W8YENu9Oa2ymNhAegdhEM=ZHww@mail.gmail.com>
Date: Tue, 12 Nov 2024 12:25:57 -0800
From: anish kumar <yesanishhere@...il.com>
To: Jonathan Corbet <corbet@....net>
Cc: linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [PATCH] drivers: core: Clarify EPROBE_DEFER retry mechanism

On Tue, Nov 12, 2024 at 12:21 PM Jonathan Corbet <corbet@....net> wrote:
>
> anish kumar <yesanishhere@...il.com> writes:
>
> > The existing documentation for EPROBE_DEFER explains its purpose
> > and usage, but does not specify when deferred probes are retried.
> > This patch adds information about the retry mechanism to provide
> > a more complete explanation of how EPROBE_DEFER works.
> >
> > Specifically, it clarifies that:
> >
> > 1. Deferred probes are added to a pending list
> > 2. A successful probe of any device triggers moving all devices
> >    from the pending list to an active list
> > 3. A workqueue processes the active list to retry deferred probes
> >
> > This additional context helps developers better understand the
> > behavior and implications of using EPROBE_DEFER in their drivers.
> >
> > Signed-off-by: anish kumar <yesanishhere@...il.com>
> > ---
> >  Documentation/driver-api/driver-model/driver.rst | 11 +++++++----
> >  1 file changed, 7 insertions(+), 4 deletions(-)
> >
> > diff --git a/Documentation/driver-api/driver-model/driver.rst b/Documentation/driver-api/driver-model/driver.rst
> > index 06f818b1d622..c86b948d0dfe 100644
> > --- a/Documentation/driver-api/driver-model/driver.rst
> > +++ b/Documentation/driver-api/driver-model/driver.rst
> > @@ -171,10 +171,13 @@ released all resources it allocated.
> >  Optionally, probe() may return -EPROBE_DEFER if the driver depends on
> >  resources that are not yet available (e.g., supplied by a driver that
> >  hasn't initialized yet).  The driver core will put the device onto the
> > -deferred probe list and will try to call it again later. If a driver
> > -must defer, it should return -EPROBE_DEFER as early as possible to
> > -reduce the amount of time spent on setup work that will need to be
> > -unwound and reexecuted at a later time.
> > +deferred probe list and will retry again as and when a device or driver
> > +gets added to the system. A successful probe of any device will trigger
> > +moving all devices from pending list to active list. A workqueue processes
> > +the active list to retry deferred probes. If a driver must defer, it
> > +should return -EPROBE_DEFER as early as possible to reduce the amount
> > +of time spent on setup work that will need to be unwound and reexecuted
> > +at a later time.
>
> Honestly, I don't see how this improves the situation?  How does this
> improve a driver developer's work?

It talks about when the retry mechanism executes. In my workplace we
had the discussion about this and some of the developers were assuming
EPROBE_DEFER gets called a fixed number of times which is not the case.
This explains when EPROBE_DEFER gets called and the mechanism for the
same.

>
> jon