linux-kernel - [PATCH v6 0/5] Functional dependencies between devices

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Message-ID: <11468990.WB1J8sxXpS@vostro.rjw.lan>
Date:   Sun, 30 Oct 2016 17:22:13 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Linux PM list <linux-pm@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     Alan Stern <stern@...land.harvard.edu>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Tomeu Vizoso <tomeu.vizoso@...labora.com>,
        Mark Brown <broonie@...nel.org>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Lukas Wunner <lukas@...ner.de>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        "Luis R. Rodriguez" <mcgrof@...e.com>
Subject: [PATCH v6 0/5] Functional dependencies between devices

Hi,

Let me quote from the previous intro messages for this series first:

> > Time for another update. :-)
> > 
> > Fewer changes this time, mostly to address issues found by Lukas and
> > Marek.
> > 
> > The most significant one is to make device_link_add() cope with the case
> > when
> > the consumer device has not been registered yet when it is called.  The
> > supplier device still is required to be registered and the function will
> > return NULL if that is not the case.
> > 
> > Another significant change is in patch [4/5] that now makes the core apply
> > pm_runtime_get_sync()/pm_runtime_put() to supplier devices around the
> > probing of a consumer one (in analogy with the parent).
> 
> One more update after some conversations during LinuxCon Europe.
> 
> The main point was to make it possible for device_link_add() to figure out
> the initial state of the link instead of expecting the caller to provide it
> which might not be reliable enough in general.
> 
> In this version device_link_add() takes three arguments, the supplier and
> consumer pointers and flags and it sets the correct initial state of the
> link automatically (unless invoked with the "stateless" flag, of course).
> The cost is one additional field in struct device (I moved all of the
> links-related fields in struct device to a separate sub-structure while at
> it) to track the "driver presence status" of the device (to be used by
> device_link_add()).
> 
> In addition to that, the links list walks in the core.c and dd.c code are
> under the device links mutex now, so the iternal link spinlock is not needed
> any more and I have renamed symbols to distinguish between flags, link
> states and device "driver presence statuses".

The most significant change in this revision with respect to the previous one is
related to the fact that SRCU is not available on some architectures, so the
code falls back to using an RW semaphore for synchronization if SRCU is not
there.  Fortunately, the code changes needed for that turned out to be quite
straightforward and confined to the second patch.

Apart from this, the flags are defined using BIT(x) now (instead of open coding
the latter in the flag definitions).

Updated is mostly patch [2/5].  Patches [1,3,5/5] have not changed (except for
trivial rebasing) and patch [4/5] needed to be refreshed on top of the modified
[2/5].

FWIW, I've run the series through 0-day which has not reported any problems
with it.

Thanks,
Rafael