irq_desc not found for my interrupt number during request_irq (radix tree of irq_desc has only 64 entries..)

Chan Kim ckim at
Tue Apr 5 21:45:33 EDT 2022

Hello all, 

I'm doing an linux driver and application test on a qemu arm64 virtual
My virtual machine is slightly modified version of arm 'virt' machine and it
has our device model included.
When I do request_irq for INTID 208 (SPI 176) in linux on my arm64 virtual
machine, it returns -EINVAL.
I poked into that function and found the desc is returning NULL in function

	int request_threaded_irq(unsigned int irq, irq_handler_t handler,
	             irq_handler_t thread_fn, unsigned long irqflags,
	             const char *devname, void *dev_id)
	    struct irqaction *action;
	    struct irq_desc *desc;
	    int retval;
	desc = irq_to_desc(irq);
	    if (!desc) 
	        return -EINVAL;

and irq_to_desc is supposed to return an irq_desc from the irq_radix_tree as
shown below.

	struct irq_desc *irq_to_desc(unsigned int irq)
	    return radix_tree_lookup(&irq_desc_tree, irq);

	void *radix_tree_lookup(const struct radix_tree_root *root, unsigned
long index)
	    return __radix_tree_lookup(root, index, NULL, NULL);

	void *__radix_tree_lookup(const struct radix_tree_root *root,
	              unsigned long index, struct radix_tree_node **nodep,
	              void __rcu ***slotp)
	    struct radix_tree_node *node, *parent;
	    unsigned long maxindex;
	    void __rcu **slot;

	    parent = NULL;
	    slot = (void __rcu **)&root->xa_head;
	    radix_tree_load_root(root, &node, &maxindex);
	    if (index > maxindex)
	        return NULL;
and I found my request index is 208 but the maxindex of the radix tree is
So it looks like the radix tree of irq_desc has been set to have maximum 64
Where and how can I set this radix tree size?
I looked at qemu's hw/arm/ab21q-build-acpi.c for MADT or DSDT table parts
but couldn't find what to add.
I have my devices address range and irq added in the DSDT and MADT.

static void
build_dsdt(GArray *table_data, BIOSLinker *linker, Ab21qMachineState *vms)
acpi_dsdt_add_axpu(scope, &memmap[AB21Q_AXPU],
                       (irqmap[AB21Q_AXPU] + ARM_SPI_BASE));
static void acpi_dsdt_add_axpu(Aml *scope, const MemMapEntry *axpu_memmap,
                                           uint32_t irq)
    Aml *dev = aml_device("AXPU");
    aml_append(dev, aml_name_decl("_HID", aml_string("AXPU0011")));
    aml_append(dev, aml_name_decl("_UID", aml_int(0)));

    Aml *crs = aml_resource_template();
    aml_append(crs, aml_memory32_fixed(axpu_memmap->base,
                                       axpu_memmap->size, AML_READ_WRITE));
               aml_interrupt(AML_CONSUMER, AML_LEVEL, AML_ACTIVE_HIGH,
                             AML_EXCLUSIVE, &irq, 1));
    aml_append(dev, aml_name_decl("_CRS", crs));

    aml_append(scope, dev);

I'm not sure if I can just use _HID value as "AXPU0011". 
If you see anything wrong and have a suggestion, please tell me.

Thank you!
Chan Kim

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