Re: [PATCH 3/3] PCI: Xilinx NWL PCIe: Fix Error for multi function device for legacy interrupts.

[Kishon Vijay Abraham I]

Hi,

On Tuesday 13 September 2016 09:04 PM, Bjorn Helgaas wrote:
> [+cc Ley Foon (altera), Thomas (aardvark), Kishon (dra7xx), Murali (keystone)]
> 
> On Tue, Sep 13, 2016 at 10:05:11AM -0500, Bjorn Helgaas wrote:
>> On Tue, Sep 13, 2016 at 08:41:28AM +0100, Marc Zyngier wrote:
>>> On 12/09/16 23:02, Bjorn Helgaas wrote:
>>>> On Thu, Sep 01, 2016 at 05:19:55AM +0000, Bharat Kumar Gogada wrote:
>>>>>>>>>> Hi Bharat,
>>>>>>>>>>> @@ -561,7 +561,7 @@ static int nwl_pcie_init_irq_domain(struct
>>>>>>>>>>> nwl_pcie
>>>>>>>>>> *pcie)
>>>>>>>>>>>     }
>>>>>>>>>>>
>>>>>>>>>>>     pcie->legacy_irq_domain = irq_domain_add_linear(legacy_intc_node,
>>>>>>>>>>> -                                                   INTX_NUM,
>>>>>>>>>>> +                                                   INTX_NUM + 1,
>>>>>>>>>>>                                                     &legacy_domain_ops,
>>>>>>>>>>>                                                     pcie);
>>>>>>>>>>
>>>>>>>>>> This feels like the wrong thing to do. You have INTX_NUM irqs, so
>>>>>>>>>> the domain allocation should reflect this. On the other hand, the
>>>>>>>>>> way the driver currently deals with mappings is quite broken
>>>>>>>>>> (consistently adding 1 to
>>>>>>>> the HW interrupt).
>>>>>>>>>>
>>>>>>>>> Hi Marc,
>>>>>>>>>
>>>>>>>>> Without above change I get following crash in kernel while booting.
>>>>>>>>>
>>>>>>>>> [    2.441684] error: hwirq 0x4 is too large for dummy
>>>>>>>>>
>>>>>>>>> [    2.441694] ------------[ cut here ]------------
>>>>>>>>>
>>>>>>>>> [    2.441698] WARNING: at kernel/irq/irqdomain.c:344
>>>>>>>>>
>>>>>>>>> [    2.441702] Modules linked in:
>>>>>>>>>
>>>>>>>>> [    2.441706]
>>>>>>>>>
>>>>>>>>> [    2.441714] CPU: 1 PID: 1 Comm: swapper/0 Not tainted 4.4.0 #8
>>>>>>>>>
>>>>>>>>> [    2.441718] Hardware name: xlnx,zynqmp (DT)
>>>>>>>>>
>>>>>>>>> [    2.441723] task: ffffffc071886b80 ti: ffffffc071888000 task.ti:
>>>>>>>> ffffffc071888000
>>>>>>>>>
>>>>>>>>> [    2.441732] PC is at irq_domain_associate+0x138/0x1c0
>>>>>>>>>
>>>>>>>>> [    2.441738] LR is at irq_domain_associate+0x138/0x1c0
>>>>>>>>>
>>>>>>>>> In kernel/irq/irqdomain.c function irq_domain_associate
>>>>>>>>>
>>>>>>>>> if (WARN(hwirq >= domain->hwirq_max,
>>>>>>>>>                  "error: hwirq 0x%x is too large for %s\n", (int)hwirq, domain-
>>>>>>> name))
>>>>>>>>>                 return -EINVAL;
>>>>>>>>>
>>>>>>>>> Here the hwirq and hwirq_max are equal to 4 without the above
>>>>>>>>> condition
>>>>>>>> (INTX_NUM + 1) due to which crash is coming.
>>>>>>>>> This is happening as the legacy interrupts are starting from 1 (INTA).
>>>>>>>>
>>>>>>>> I understood that. I'm still persisting in saying that you have the wrong fix.
>>>>>>>>
>>>>>>>> Your domain should always allocate many interrupts as you have
>>>>>>>> interrupt sources. These interrupts (hwirq) should be numbered from 0 to (n-
>>>>>> 1).
>>>>>>>
>>>>>>> Agreed, but here comes the problem the hwirq for legacy interrupts
>>>>>>> will start at 0x1 to 0x4 (INTA to INTD) and these values are as per
>>>>>>> PCIe specification for legacy interrupts. So these cannot be numbered
>>>>>>> from 0. So when 0x4 (INTD) for a multi-function device comes the crash
>>>>>>> occurs.
>>>>>>
>>>>>> So who provides this hwirq? Who calls irq_domain_associate() with hwirq set to
>>>>>> 4?
>>>>>>
>>>>> PCIe subsystem invokes pcibios_add_device function in arch/arm64/kernel/pci.c for every pci device.
>>>>> The purpose of this function is to assign dev->irq using of_irq_parse_and_map_pci.
>>>>> of_irq_parse_and_map_pci invokes of_irq_parse_pci where it reads PCI_INTERRUPT_PIN from configuration space and saves it
>>>>> in parameter of struct of_phandle_args.
>>>>> This structure is passed to irq_create_of_mapping where it invokes irq_create_fwspec_mapping.
>>>>> irq_create_fwspec_mapping invokes irq_domain_translate and gets hwirq, here the above saved PCI_INTERRUPT_PIN value is assigned 
>>>>> to hwirq (*hwirq = fwspec->param[0]).
>>>>> And then using this hwirq irq_create_mapping -> irq_domain_associate were invoked and mapping is created for virtual irq with this hwirq.
>>>>> So for any end point PCI_INTERRUPT_PIN value starts from 0x1 to 0x4 and so hwirq starts from 0x1 to 0x4.
>>>>>
>>>>> So the values are more generic w.r.t to protocol, that's why hwirq will range from 0x1 to 0x4. 
>>>>> And then if you check pcie-altera.c they are doing this adding one in their handler and while creating legacy domain.
>>>>
>>>> Is this resolved yet?  Marc, are you happy, or should we iterate on this
>>>> again?
>>>
>>> Ah, sorry to have dropped the ball on this patch.
>>
>> No problem, I wasn't making forward progress anyway.
>>
>>> I guess that given that the infrastructure imposes the hwirq range on
>>> the host drivers, Bharat's approach is the only way (and a number of
>>> other host drivers are already slightly broken). I'll try and have a
>>> look at solving this at the generic level. In the meantime:
>>>
>>> Acked-by: Marc Zyngier <marc.zyngier@xxxxxxx>
>>
>> After looking at this myself, I'm not happy with this either.  It feels
>> like there are bugs lurking here and we're just hiding one of them.
>>
>> Here are the callers of irq_domain_add_linear() for legacy INTx in
>> drivers/pci/host:
>>
>>   advk_pcie_init_irq_domain    LEGACY_IRQ_NUM   (4)
>>   dra7xx_pcie_init_irq_domain  4
>>   ks_dw_pcie_host_init         MAX_LEGACY_IRQS  (4)
>>   altera_pcie_init_irq_domain  INTX_NUM + 1     (5)
>>   nwl_pcie_init_irq_domain     INTX_NUM + 1     (5)
>>   xilinx_pcie_init_irq_domain  4
> 
> The altera change corresponding to this was 99496bd2971f ("PCI: altera: Fix
> error when INTx is 4").  I should have noticed this inconsistency back
> then.
> 
> Are aardvark, dra7xx, keystone, and xilinx (non-NWL) broken because they
> only request 4 IRQs and only INTA, INTB, and INTC work?

yeah.. it's broken in dra7xx. I get [1] when I configure the pci endpoint to
use INTD.

Thanks
Kishon

[1] -> http://pastebin.ubuntu.com/23177268/
> 
>> I think all of these use the of_irq_parse_and_map_pci() path you
>> mentioned, so if the problem is in the way that path works, I would
>> think these should *all* be requesting the same number of interrupts
>> in the domain.
>>
>> I agree with Marc that we should request 4 IRQs, because that's what
>> we need.  If we can't do that for some reason, we ought to at least
>> make all these callers the same.
>>
>> Bjorn
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