linux-kernel - Re: [PATCH 3/5] irqchip/gic-v2: Parse and export virtual GIC information

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Date:	Tue, 9 Feb 2016 11:31:55 +0000
From:	Marc Zyngier <marc.zyngier@....com>
To:	Julien Grall <julien.grall@....com>, kvmarm@...ts.cs.columbia.edu
Cc:	christoffer.dall@...aro.org, fu.wei@...aro.org,
	kvm@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, wei@...hat.com,
	al.stone@...aro.org, Thomas Gleixner <tglx@...utronix.de>,
	Jason Cooper <jason@...edaemon.net>
Subject: Re: [PATCH 3/5] irqchip/gic-v2: Parse and export virtual GIC
 information

On 09/02/16 11:23, Julien Grall wrote:
> On 08/02/16 18:30, Marc Zyngier wrote:
>> Julien,
> 
> Hi Marc,
> 
>> On 08/02/16 16:47, Julien Grall wrote:
> 
> [...]
> 
>>> +static void __init gic_of_setup_kvm_info(struct device_node *node)
>>> +{
>>> +	int ret;
>>> +	struct resource r;
>>> +	unsigned int irq;
>>> +
>>> +	gic_v2_kvm_info.type = GIC_V2;
>>> +
>>> +	irq = irq_of_parse_and_map(node, 0);
>>> +	if (!irq)
>>> +		gic_v2_kvm_info.maint_irq = -1;
>>
>> Please don't do that. 0 *is* the value for an invalid interrupt, and
>> this is what you should expose here. Same for GICv3.
> 
> I decided to use -1, because the function acpi_register_gsi is returning 
> a negative value when an error occurred.
> 
> AFAICT, returning 0 would be a valid value for acpi_register_gsi.

No really. It either returns -EINVAL, or the result of
irq_create_fwspec_mapping, which is either going to return a virtual
interrupt number (strictly positive), or zero if the mapping was impossible.

So anything <= 0 is an error, and you can use 0 to indicate it. In
general, there is no such thing as IRQ0 (if you're not convinced, please
argue with Linus: http://yarchive.net/comp/linux/zero.html).

>>> +	else
>>> +		gic_v2_kvm_info.maint_irq = irq;
>>> +
>>> +	ret = of_address_to_resource(node, 2, &r);
>>> +	if (!ret) {
>>> +		gic_v2_kvm_info.vctrl_base = r.start;
>>> +		gic_v2_kvm_info.vctrl_size = resource_size(&r);
>>> +	}
>>> +
>>> +	ret = of_address_to_resource(node, 3, &r);
>>> +	if (!ret) {
>>> +		if (!PAGE_ALIGNED(r.start))
>>> +			pr_warn("GICV physical address 0x%llx not page aligned\n",
>>> +				(unsigned long long)r.start);
>>> +		else if (!PAGE_ALIGNED(resource_size(&r)))
>>> +			pr_warn("GICV size 0x%llx not a multiple of page size 0x%lx\n",
>>> +				(unsigned long long)resource_size(&r),
>>> +				PAGE_SIZE);
>>> +		else {
>>> +			gic_v2_kvm_info.vcpu_base = r.start;
>>> +			gic_v2_kvm_info.vcpu_size = resource_size(&r);
>>
>> This tends to make me think that this should actually be a proper
>> resource, and not a set of arbitrary fields.
> 
> I will give a look.
> 
> [..]
> 
>>> @@ -1270,6 +1338,12 @@ gic_acpi_parse_madt_cpu(struct acpi_subtable_header *header,
>>>   		return -EINVAL;
>>>
>>>   	cpu_phy_base = gic_cpu_base;
>>> +	acpi_data.maint_irq = processor->vgic_interrupt;
>>> +	acpi_data.maint_irq_mode = (processor->flags & ACPI_MADT_VGIC_IRQ_MODE) ?
>>> +				    ACPI_EDGE_SENSITIVE : ACPI_LEVEL_SENSITIVE;
>>> +	acpi_data.vctrl_base = processor->gich_base_address;
>>> +	acpi_data.vcpu_base = processor->gicv_base_address;
>>> +
>>
>> Maybe you can now move all the ACPI data into this acpi_data structure?
>> This would allow for slightly less clutter...
> 
> Good idea, I will do it in the next version.

Thanks,

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