linux-kernel - Re: [PATCH 01/10] of: Keep track of populated platform devices

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Message-Id: <20140429125657.65910C4089D@trevor.secretlab.ca>
Date:	Tue, 29 Apr 2014 13:56:57 +0100
From:	Grant Likely <grant.likely@...aro.org>
To:	Rob Herring <robherring2@...il.com>,
	Pawel Moll <pawel.moll@....com>
Cc:	Rob Herring <robh+dt@...nel.org>,
	Samuel Ortiz <sameo@...ux.intel.com>,
	Lee Jones <lee.jones@...aro.org>,
	Arnd Bergmann <arnd@...db.de>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Russell King <linux@....linux.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	"arm@...nel.org" <arm@...nel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH 01/10] of: Keep track of populated platform devices

On Mon, 28 Apr 2014 13:02:28 -0500, Rob Herring <robherring2@...il.com> wrote:
> On Mon, Apr 28, 2014 at 12:57 PM, Pawel Moll <pawel.moll@....com> wrote:
> > In "Device Tree powered" systems, platform devices are usually
> > massively populated with of_platform_populate() call, executed
> > at some level of initcalls, either by generic architecture
> > or by platform-specific code.
> >
> > There are situations though where certain devices must be
> > created (and bound with drivers) before all the others.
> > This presents a challenge, as devices created explicitly
> > would be created again by of_platform_populate().
> >
> > This patch tries to solve that issue in a generic way,
> > adding a "populated" flag for a DT node description.
> > Once set, this device will never be created again via
> > of_* API, so of_platform_populate() will skip such nodes
> > (and its children) in a similar way to the non-available
> > ones.
> >
> > Cc: devicetree@...r.kernel.org
> > Signed-off-by: Pawel Moll <pawel.moll@....com>
> > ---
> >  drivers/of/platform.c | 10 ++++++++--
> >  include/linux/of.h    |  1 +
> >  2 files changed, 9 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> > index 404d1da..0ae757a 100644
> > --- a/drivers/of/platform.c
> > +++ b/drivers/of/platform.c
> > @@ -204,7 +204,8 @@ static struct platform_device *of_platform_device_create_pdata(
> >  {
> >         struct platform_device *dev;
> >
> > -       if (!of_device_is_available(np))
> > +       if (!of_device_is_available(np) ||
> > +                       of_node_check_flag(np, OF_POPULATED))
> 
> This and the amba case should be a test_and_set operation to avoid a
> race condition.

Yes. It is an unlikely condition at the time that Pawel is handling, but
it should also work for later calls to of_platform_populate() which may
happen at runtime and in parallel.

g.
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