Date:	Mon, 21 Apr 2014 14:01:05 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Tony Lindgren <tony@...mide.com>,
	Russell King - ARM Linux <linux@....linux.org.uk>
CC:	"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

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).

>> 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.

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;
+}
+EXPORT_SYMBOL_GPL(of_irq_get);
+
+/**
  * of_irq_count - Count the number of IRQs a node uses
  * @dev: pointer to device tree node
  */
--
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