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

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Date:   Thu, 21 Jul 2022 14:58:27 -0700
From:   Saravana Kannan <saravanak@...gle.com>
To:     "Russell King (Oracle)" <linux@...linux.org.uk>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        Rob Herring <robh@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        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, Jul 21, 2022 at 1:50 AM Russell King (Oracle)
<linux@...linux.org.uk> 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

Where am I supposed to add that? Just somewhere in the email body?

The patch you are replying to was based on your linu-arm/for-next the
day I sent it. Do you still need me to rebase it on Linus's tree?

> the patch was generated against (just the tagged version is sufficient)
> somewhere in the email, and send it to patches@...linu.org.uk.

I'll send out the same patch as is to that email. Wait, is there a
typo in the domain name? Did you leave out the x by accident or is it
really armlinu? I'm also getting a DNS failure for either one of those
domains.

I'll wait to hear from you before I send another email.

-Saravana

>
> Thanks.
>
> --
> RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
> FTTP is here! 40Mbps down 10Mbps up. Decent connectivity at last!