[PATCH v2] of: Keep track of populated platform devices

[Grant Likely]

On Wed, 30 Apr 2014 10:22:25 -0500, Rob Herring <robherring2 at gmail.com> wrote:
> On Wed, Apr 30, 2014 at 9:05 AM, Pawel Moll <pawel.moll at arm.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.
> >
> > Signed-off-by: Pawel Moll <pawel.moll at arm.com>
> 
> One pondering and one minor change below, otherwise:
> 
> Acked-by: Rob Herring <robh at kernel.org>
> 
> 
> > ---
> >
> > Changes since v1:
> >
> > - added of_node_check_and_set_flag()... (atomic test and set)
> > - ... used it to atomically mark a node...
> > - ... clearing the bit on error path.
> >
> >  drivers/of/platform.c | 18 +++++++++++++-----
> >  include/linux/of.h    |  7 +++++++
> >  2 files changed, 20 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/of/platform.c b/drivers/of/platform.c
> > index 404d1da..b33927a 100644
> > --- a/drivers/of/platform.c
> > +++ b/drivers/of/platform.c
> > @@ -204,12 +204,13 @@ 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_and_set_flag(np, OF_POPULATED))
> >                 return NULL;
> >
> >         dev = of_device_alloc(np, bus_id, parent);
> >         if (!dev)
> > -               return NULL;
> > +               goto err_clear_flag;
> 
> I wonder if leaving it set would be the right behavior. I can't see
> that we would want to process the node again. But this is the
> exceptional case, so its probably not too important and can stay like
> this.

That doesn't work in the case where drivers use of_platform_populate().
MFD devices in particular make use of it. If the driver does not get
cleared on removal of the devices, then all MFD users will be broken on
driver unbind/rebind. *

We really need to have the inverse of of_platform_populate which will
remove all child and child's child devices and clear all flags and such.
Right now moany drivers are open-coding the removal.

* most drivers are somewhat broken on unbind/rebind anyway, but I don't
  want to make it impossible for a driver to get it right.

> 
> >
> >  #if defined(CONFIG_MICROBLAZE)
> >         dev->archdata.dma_mask = 0xffffffffUL;
> > @@ -227,10 +228,14 @@ static struct platform_device *of_platform_device_create_pdata(
> >
> >         if (of_device_add(dev) != 0) {
> >                 platform_device_put(dev);
> > -               return NULL;
> > +               goto err_clear_flag;
> >         }
> >
> >         return dev;
> > +
> > +err_clear_flag:
> > +       of_node_clear_flag(np, OF_POPULATED);
> > +       return NULL;
> >  }
> >
> >  /**
> > @@ -262,14 +267,15 @@ static struct amba_device *of_amba_device_create(struct device_node *node,
> >
> >         pr_debug("Creating amba device %s\n", node->full_name);
> >
> > -       if (!of_device_is_available(node))
> > +       if (!of_device_is_available(node) ||
> > +                       of_node_check_and_set_flag(node, OF_POPULATED))
> >                 return NULL;
> >
> >         dev = amba_device_alloc(NULL, 0, 0);
> >         if (!dev) {
> >                 pr_err("%s(): amba_device_alloc() failed for %s\n",
> >                        __func__, node->full_name);
> > -               return NULL;
> > +               goto err_clear_flag;
> >         }
> >
> >         /* setup generic device info */
> > @@ -309,6 +315,8 @@ static struct amba_device *of_amba_device_create(struct device_node *node,
> >
> >  err_free:
> >         amba_device_put(dev);
> > +err_clear_flag:
> > +       of_node_clear_flag(node, OF_POPULATED);
> >         return NULL;
> >  }
> >  #else /* CONFIG_ARM_AMBA */
> > diff --git a/include/linux/of.h b/include/linux/of.h
> > index 3bad8d1..534cab8 100644
> > --- a/include/linux/of.h
> > +++ b/include/linux/of.h
> > @@ -130,6 +130,12 @@ static inline int of_node_check_flag(struct device_node *n, unsigned long flag)
> >         return test_bit(flag, &n->_flags);
> >  }
> >
> > +static inline int of_node_check_and_set_flag(struct device_node *n,
> 
> Please keep the well known naming convention of the called function:
> of_node_test_and_set_flag