linux-kernel - Re: [PATCH v6] amba: Remove deferred device addition

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Date:   Wed, 27 Jul 2022 23:16:08 +0100
From:   "Russell King (Oracle)" <linux@...linux.org.uk>
To:     Saravana Kannan <saravanak@...gle.com>
Cc:     Philipp Zabel <p.zabel@...gutronix.de>,
        Rob Herring <robh@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Linus Walleij <linus.walleij@...aro.org>,
        Sudeep Holla <sudeep.holla@....com>,
        Nicolas Saenz Julienne <nsaenz@...nel.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>,
        patches@...linux.org.uk, kernel-team@...roid.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v6] amba: Remove deferred device addition

On Wed, Jul 27, 2022 at 11:19:35AM -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.

Oh, this is absolutely horrible. I can apply it cleanly to my "misc"
branch, but it then conflicts when I re-merge my tree for the for-next
thing (which is only supposed to be for sfr - the hint is in the name!)
for-next is basically my "fixes" plus "misc" branch and anything else I
want sfr to pick up for the -next tree.

Applying this has to be on top of that merge commit, otherwise the
conflicts are horrid, but that then means I need to send Linus the
for-next merge commit (which I don't normally do.)

Gah, we have too many changes to drivers/bus/amba.c in this cycle,
some of them which have been submitted for 5.19 as fixes (and thus
are not in 5.18-rc1 which the misc branch is based upon for other
patch dependency reasons) and others in the misc branch for the next
cycle - and now your patch wants both, which I can't do without
rebasing the misc branch.

Sadly, getting these changes into GregKH's tree will just create a
conflict between Greg's tree and my tree.

Can we postpone this please?

-- 
RMK's Patch system: https://www.armlinux.org.uk/developer/patches/
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