linux-kernel - Re: [PATCH 6/6] regulator: core: simplify lock

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Message-ID: <ZO0DDkNUZ4FwYTrz@qmqm.qmqm.pl>
Date:   Mon, 28 Aug 2023 22:26:54 +0200
From:   Michał Mirosław <mirq-linux@...e.qmqm.pl>
To:     Doug Anderson <dianders@...omium.org>
Cc:     Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>, linux-kernel@...r.kernel.org,
        Dmitry Osipenko <digetx@...il.com>,
        Stephen Boyd <swboyd@...omium.org>
Subject: Re: [PATCH 6/6] regulator: core: simplify lock_two()

On Mon, Aug 21, 2023 at 09:51:08AM -0700, Doug Anderson wrote:
> Hi,
> 
> On Sat, Aug 19, 2023 at 3:46 PM Michał Mirosław <mirq-linux@...e.qmqm.pl> wrote:
> >
> > Make regulator_lock_two() shorter by observing that we have only two
> > locks and when swapped earlier the retry code becomes identical to the
> > normal (optimistic) path.
> >
> > Signed-off-by: Michał Mirosław <mirq-linux@...e.qmqm.pl>
> > ---
> >  drivers/regulator/core.c | 28 ++++++++++------------------
> >  1 file changed, 10 insertions(+), 18 deletions(-)
> 
> This is quite nearly a direct revert of commit 37473397b852
> ("regulator: core: Make regulator_lock_two() logic easier to follow"),
> which was requested by Stephen in:
> 
> https://lore.kernel.org/r/CAE-0n53Eb1BeDPmjBycXUaQAF4ppiAM6UDWje_jiB9GAmR8MMw@mail.gmail.com
> 
> I don't personally have a strong opinion, but do prefer not to flip-flop. ;-)

Indeed they are quite similar. I did remove a bit more code than that,
though: in this case there is no early success return before the loop.

Instead of saying:

lock A
lock B
if ok return
if that failed, loop:
  unlock A
  lock B harder
  lock A
  if ok return
  swap A <-> B
  lock B

Now it's:

lock A
loop forever:
  lock B
  if ok, return
  unlock A
  swap them
  lock A harder

With the same condition 'A held' at the start of an iteration.

Best Regards
Michał Mirosław