Re: [RFC PATCH] of: platform: Skip mapping of interrupts in of_device_alloc()

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On 2021-12-09 00:10, Lad Prabhakar wrote:
of_device_alloc() in early boot stage creates a interrupt mapping if
there exists a "interrupts" property in the node.

For hierarchical interrupt domains using "interrupts" property in the node
bypassed the hierarchical setup and messed up the irq setup.

This patch adds a check in of_device_alloc() to skip interrupt mapping if
"not-interrupt-producer" property is present in the node. This allows
nodes to describe the interrupts using "interrupts" property.

Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@xxxxxxxxxxxxxx>
---
Hi All,

Spawning from discussion [1], here is simple patch (not the ideal probably welcome for suggestions) from stopping the OF code from creating a map for
the interrupts when using "interrupts" property.

[1] https://lore.kernel.org/lkml/87pmqrck2m.wl-maz@xxxxxxxxxx/
    T/#mbd1e47c1981082aded4b32a52e2c04291e515508

Cheers,
Prabhakar
---
 drivers/of/platform.c | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/drivers/of/platform.c b/drivers/of/platform.c
index b3faf89744aa..629776ca1721 100644
--- a/drivers/of/platform.c
+++ b/drivers/of/platform.c
@@ -114,7 +114,7 @@ struct platform_device *of_device_alloc(struct
device_node *np,
 				  struct device *parent)
 {
 	struct platform_device *dev;
-	int rc, i, num_reg = 0, num_irq;
+	int rc, i, num_reg = 0, num_irq = 0;
 	struct resource *res, temp_res;

 	dev = platform_device_alloc("", PLATFORM_DEVID_NONE);
@@ -124,7 +124,14 @@ struct platform_device *of_device_alloc(struct
device_node *np,
 	/* count the io and irq resources */
 	while (of_address_to_resource(np, num_reg, &temp_res) == 0)
 		num_reg++;
-	num_irq = of_irq_count(np);
+
+	/*
+ * we don't want to map the interrupts of hierarchical interrupt domain + * into the parent domain yet. This will be the job of the hierarchical
+	 * interrupt driver code to map the interrupts as and when needed.
+	 */
+	if (!of_property_read_bool(np, "not-interrupt-producer"))

I don't think this is right. If anything, the expected behaviour should be
indicated by the driver and not the device node.

+		num_irq = of_irq_count(np);

 	/* Populate the resource table */
 	if (num_irq || num_reg) {
@@ -140,7 +147,7 @@ struct platform_device *of_device_alloc(struct
device_node *np,
 			rc = of_address_to_resource(np, i, res);
 			WARN_ON(rc);
 		}
-		if (of_irq_to_resource_table(np, res, num_irq) != num_irq)
+ if (num_irq && of_irq_to_resource_table(np, res, num_irq) != num_irq)
 			pr_debug("not all legacy IRQ resources mapped for %pOFn\n",
 				 np);
 	}

The root of the issue is that all the resource allocation is done upfront,
way before we even have a driver that could potentially deal with this
device. This is a potential waste of resource, and it triggers the
issue you noticed.

If you delay the resource allocation until there is an actual match with a
driver, you could have a per-driver flag telling you whether the IRQ
allocation should be performed before the probe() function is called.

        M.
--
Jazz is not dead. It just smells funny...



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