Date:	Mon, 21 Apr 2014 13:25:47 -0700
From:	Tony Lindgren <tony@...mide.com>
To:	Rob Herring <robherring2@...il.com>
Cc:	Russell King - ARM Linux <linux@....linux.org.uk>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Jean-Jacques Hiblot <jjhiblot@...phandler.com>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Grant Likely <grant.likely@...retlab.ca>,
	Rob Herring <robh+dt@...nel.org>,
	Gregory Clement <gregory.clement@...e-electrons.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v3 2/2] dt: platform driver: Fill the resources before
 probe and defer if needed

* Rob Herring <robherring2@...il.com> [140421 12:01]:
> On Mon, Apr 21, 2014 at 10:54 AM, Tony Lindgren <tony@...mide.com> wrote:
> > * Rob Herring <robherring2@...il.com> [140421 06:47]:
> >> On Fri, Apr 18, 2014 at 6:24 PM, Tony Lindgren <tony@...mide.com> wrote:
> >> > * Russell King - ARM Linux <linux@....linux.org.uk> [140418 16:04]:
> >> >> On Fri, Apr 18, 2014 at 02:58:48PM -0700, Tony Lindgren wrote:
> >> >> > Oh come on, let's stop pretending it's not broken. And it's way worse with
> >> >> > device tree as there's nothing making sure the resources for a driver
> >> >> > are set up before the driver probes. And we've been unable to fix just
> >> >> > this issue alone for about six months now. It's also broken beyond that.
> >> >> > It's called of_platform_bus yet it won't even pass the platform_data
> >> >> > as auxdata to the devices on a sub-bus instantatiated like I2C.
> >> >>
> >> >> Isn't there a much simpler solution to the platform device IRQ problem?
> >> >>
> >> >> Rather than trying to fix it at the point where the resources are
> >> >> created, why not just *not* have DT create the IRQ resources in the
> >> >> first place, and instead have platform_get_irq() (which is the function
> >> >> which should be used to get an IRQ) be the actor to do whatever is
> >> >> necessary to return the IRQ(s) ?
> >> >
> >> > Yeah why not. I don't see why we would need to do all this of_* special
> >> > trickery for much anything beyond parsing the binding.
> >>
> >> That can work, but it will still need something like
> >> of_find_irq_domain() to determine whether to return -EPROBE_DEFER or
> >> not.
> >
> > Right. Naturally let's do whatever it takes to first fix this issue
> > in a minimal way first for the -rc cycle so we can do the longer term
> > changes needed.
> 
> I'm not really convinced there is a simple and safe enough solution for
> 3.15. We should also be willing to tag a solution for stable if we take
> it for -rc (although that decision could be deferred).

Yes the fix needs to also go to stable. And this is a regression
between legacy booting and DT based booting so we do have good
reasons to fix this for the -rc cycle. Who knows how many people are
hitting this and are tinkering with the driver initcall levels to
work around it. Ideally the fix, even if intrusive, would already
get us a little bit into the right direction.

> >> You could also go in the other direction and don't create the device
> >> until the resources can be resolved. Unlike any of the other
> >> solutions, that would work for amba bus as well although we may never
> >> have a case where we need this with the amba bus. This would require
> >> making of_platform_populate be callable multiple times, but there are
> >> already some other reasons for wanting to do that. Specifically, I
> >> would like the core code to call of_platform_populate with default
> >> options and then only platforms with non-default options need a call
> >> to of_platform_populate.
> >
> > I like this idea as this would also probably remove the the numerous
> > dmesg errors we are currently getting for drivers reprobing with
> > -EPROBE_DEFER.
> 
> One issue with my proposal is with supporting modules. IIUC, deferred
> probe will continue trying forever and loading modules can cause probe
> to succeed. If devices are not created and on the deferred probe list,
> then they will not get probed when a module load fixes the dependency.
> 
> > In the long term we should have platform bus just call a set of
> > standardized functions implemented by whatever the data source might
> > be. That way we can limit the use of of_* functions in device drivers
> > to just parsing of custom bindings in the drivers and use bus specific
> > functions for everything else.
> >
> >> >> Yes, I know we have some drivers which use platform_get_resources() with
> >> >> IORESOURCE_IRQ, but they should really use the right accessor.  And those
> >> >> who just dereference the resource array directly... get what's coming
> >> >> (though of course they have to be fixed.)
> >> >
> >> > $ git grep IORESOURCE_IRQ drivers/ | grep platform_get_resource | wc -l
> >> > 179
> >>
> >> Certainly, this is worthwhile clean-up no matter what the solution.
> >
> > Yeah agreed. But let's also consider the IORESOURCE_IRQ as just another
> > source for for the bus or driver data in addition to the DT parsed data.
> > Both sources of data should work just fine with platform_bus even
> > without cleaning up the drivers
> 
> Ah, right. Except for those drivers you need to work with deferred probe
> would have to use platform_get_irq. That fact makes this solution quite
> a bit easier.

Yes fixing up the known broken drivers is also doable for the -rc
cycle.
 
> Something like this is what you had in mind?
> 
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index e714709..5b47210 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -13,6 +13,7 @@
>  #include <linux/string.h>
>  #include <linux/platform_device.h>
>  #include <linux/of_device.h>
> +#include <linux/of_irq.h>
>  #include <linux/module.h>
>  #include <linux/init.h>
>  #include <linux/dma-mapping.h>
> @@ -87,7 +88,11 @@ int platform_get_irq(struct platform_device *dev,
> unsigned int num)
>  		return -ENXIO;
>  	return dev->archdata.irqs[num];
>  #else
> -	struct resource *r = platform_get_resource(dev, IORESOURCE_IRQ, num);
> +	struct resource *r;
> +	if (IS_ENABLED(CONFIG_OF_IRQ) && dev->dev.of_node)
> +		return of_irq_get(dev->dev.of_node, num);
> +
> +	r = platform_get_resource(dev, IORESOURCE_IRQ, num);
> 
>  	return r ? r->start : -ENXIO;
>  #endif
> diff --git a/drivers/of/irq.c b/drivers/of/irq.c
> index 7d3184f..30449ad 100644
> --- a/drivers/of/irq.c
> +++ b/drivers/of/irq.c
> @@ -400,6 +400,26 @@ int of_irq_to_resource(struct device_node *dev, int
> index, struct resource *r)
>  EXPORT_SYMBOL_GPL(of_irq_to_resource);
> 
>  /**
> + * of_irq_get - Decode a node's IRQ and return it as a Linux irq number
> + * @dev: pointer to device tree node
> + * @index: zero-based index of the irq
> + *
> + * Returns Linux irq number on success, or -EPROBE_DEFER if the irq domain
> + * is not yet created.
> + *
> + */
> +int of_irq_get(struct device_node *dev, int index)
> +{
> +	int irq = irq_of_parse_and_map(dev, index);
> +
> +	if (!irq && of_find_irq_domain(dev, index) == NULL)
> +		return -EPROBE_DEFER;
> +
> +	return irq;
> +}

Yeah something like that. That might also work as a pretty
minimal fix as long as we fix the known broken drivers to use
platform_get_irq().

But for the long run, how about we define some kind of Linux
generic bus ops:

struct bus_ops {
	struct resource *	(*get_resource)(struct device *dev, unsigned int type, unsigned int num);
	int			(get_irq)(struct device *dev, unsigned int num);
	...
};

And then DT code would register static of_irq_get() as a get_irq()
for the platform_bus. And naturally we'd implement these functions
for legacy resources too. And that way platform_bus code stays clear
of implementation details and just goes through the list of
registered data sources. It may even make sense to do it for the
fix to keep the of_* functions private to drivers/of/*.c and the
bus code generic.

> +EXPORT_SYMBOL_GPL(of_irq_get);

Probably no need to export this? I don't think we want other
code to use this directly..

Regards,

Tony
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