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

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Date:   Wed, 31 Aug 2016 11:56:49 +0100
From:   Marc Zyngier <marc.zyngier@....com>
To:     Bharat Kumar Gogada <bharat.kumar.gogada@...inx.com>,
        "robh@...nel.org" <robh@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "colin.king@...onical.com" <colin.king@...onical.com>,
        Soren Brinkmann <sorenb@...inx.com>,
        Michal Simek <michals@...inx.com>,
        "arnd@...db.de" <arnd@...db.de>
Cc:     "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Ravikiran Gummaluri <rgummal@...inx.com>
Subject: Re: [PATCH 3/3] PCI: Xilinx NWL PCIe: Fix Error for multi function
 device for legacy interrupts.

On 31/08/16 10:56, Bharat Kumar Gogada wrote:
>  > On 30/08/16 15:13, 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?

>>
>>> And I'm  consistently adding 1 to the HW interrupt as in
>>> nwl_pcie_leg_handler I get 0th bit set from MSGF_LEG_STATUS if INTA
>>> interrupt is raised but my hwirq number being mapped for INTA is 0x1
>>> so that's I'm adding 1 to obtain correct virtual irq. Same case in
>>> nwl_pcie_free_irq_domain since hwirq starts from one I'm adding 1 to
>>> obtain virtual irq and free it.
>>
>> I can see that. Nonetheless, this is wrong. Can you please test the patch I
>> provided in my reply and report what happens?
> 
> Can you be more specific on what is the wrong, I'm adding one since
> the hwirq starts from 0x1 as mentioned above.

hwirq should always be the value that is reported by the HW. In your
case, this ranges from 0 to 3, never 4. So if we can understand why you
get called with 4 as a hwirq, we can fix this properly, for everyone. It
is also worth noting that other drivers do not have to do this +1 dance.

> I did try your suggestion with Ethernet card, but kernel hangs (it
> does not show any crash also, just hangs) when I do interface up
> (without bit + 1, using only bit position in handler). This is not
> working because in the legacy domain virq mapping starts with hwirq
> 0x1, there is no mapping for 0x0 in the domain, so EP interrupt is
> not serviced since virq being returned is zero.

Right. So let's go back to first principles and find out *who* decides
about the hwirq starting at 1 instead of zero.

Thanks,

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