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

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Date:   Tue, 8 Nov 2016 21:14:32 +0100
From:   "Luis R. Rodriguez" <mcgrof@...nel.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     "Luis R. Rodriguez" <mcgrof@...nel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Linux PM list <linux-pm@...r.kernel.org>,
        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>,
        Lukas Wunner <lukas@...ner.de>,
        Kevin Hilman <khilman@...nel.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Joerg Roedel <joro@...tes.org>, Jiri Kosina <jkosina@...e.cz>,
        Jiri Slaby <jslaby@...e.com>,
        Andrzej Hajda <a.hajda@...sung.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Lars-Peter Clausen <lars@...afoo.de>,
        Grant Likely <grant.likely@...retlab.ca>
Subject: Re: [PATCH v6 0/5] Functional dependencies between devices

On Tue, Nov 08, 2016 at 07:36:45AM +0100, Marek Szyprowski wrote:
> Hi Luis,
> 
> 
> On 2016-11-07 22:15, Luis R. Rodriguez wrote:
> > On Wed, Nov 02, 2016 at 08:58:38AM +0100, Marek Szyprowski wrote:
> > > On 2016-10-31 18:47, Greg Kroah-Hartman wrote:
> > > > On Sun, Oct 30, 2016 at 05:22:13PM +0100, Rafael J. Wysocki wrote:
> > > > > 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.
> > > > Great, they are now applied to my tree, thanks again for doing this
> > > > work.
> > > Thanks for merging those patches! Could you provide a stable tag with them,
> > > so I can
> > > ask Joerg to merge my Exynos IOMMU PM patches on top of it via IOMMU tree?
> > You want these patches to be merged into stable?! This is a whole new set of
> > functionality, the patches in no way describe any *fixes* or critical issues,
> > why are you saying this is needed? What makes you believe this is a stable
> > candidate?
> 
> I don't want to merge those patches to stale kernel release. By 'stable tag'
> I just meant something that can be pulled by Joerg to have a base for my
> Exynos IOMMU patches.

Phew! Thanks for the clarification!

  Luis