linux-kernel - Re: [PATCH v5] amba: Remove deferred device addition

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Date:   Thu, 21 Jul 2022 12:30:18 +0100
From:   Lee Jones <lee@...nel.org>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Saravana Kannan <saravanak@...gle.com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Rob Herring <robh@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        Geert Uytterhoeven <geert+renesas@...der.be>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Kefeng Wang <wangkefeng.wang@...wei.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        kernel-team@...roid.com, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v5] amba: Remove deferred device addition

On Thu, 21 Jul 2022, Russell King (Oracle) wrote:

> On Wed, Jul 20, 2022 at 02:12:21PM +0100, Sudeep Holla wrote:
> > On Tue, Jul 19, 2022 at 11:20:10AM -0700, Saravana Kannan wrote:
> > > The uevents generated for an amba device need PID and CID information
> > > that's available only when the amba device is powered on, clocked and
> > > out of reset. So, if those resources aren't available, the information
> > > can't be read to generate the uevents. To workaround this requirement,
> > > if the resources weren't available, the device addition was deferred and
> > > retried periodically.
> > > 
> > > However, this deferred addition retry isn't based on resources becoming
> > > available. Instead, it's retried every 5 seconds and causes arbitrary
> > > probe delays for amba devices and their consumers.
> > > 
> > > Also, maintaining a separate deferred-probe like mechanism is
> > > maintenance headache.
> > > 
> > > With this commit, instead of deferring the device addition, we simply
> > > defer the generation of uevents for the device and probing of the device
> > > (because drivers needs PID and CID to match) until the PID and CID
> > > information can be read. This allows us to delete all the amba specific
> > > deferring code and also avoid the arbitrary probing delays.
> > > 
> > > Cc: Rob Herring <robh@...nel.org>
> > > Cc: Ulf Hansson <ulf.hansson@...aro.org>
> > > Cc: Saravana Kannan <saravanak@...gle.com>
> > > Cc: Linus Walleij <linus.walleij@...aro.org>
> > > Cc: Sudeep Holla <sudeep.holla@....com>
> > 
> > Tested-by: Sudeep Holla <sudeep.holla@....com>
> > 
> > on Juno with linux-next(which had the reported issue [1]) + this patch(which
> > fixes the issue)
> 
> Ok, but this patch needs to end up in the patch system for me to apply
> it. Can someone please add "KernelVersion: 5.19-rc7" or whatever version
> the patch was generated against (just the tagged version is sufficient)
> somewhere in the email, and send it to patches@...linu.org.uk.

If this is a part of the submission process for the subsystems/files
you maintain, do you think it would be worth while adding this address
to MAINTAINERS to make it easier for future contributors?