Re: [PATCH v2 2/2] PCI: controller: dwc: add UniPhier PCIe host controller support

[Kishon Vijay Abraham I <kishon@ti.com>]

Hi Lorenzo,

On Friday 28 September 2018 09:13 PM, Lorenzo Pieralisi wrote:
> On Fri, Sep 28, 2018 at 02:17:16PM +0100, Marc Zyngier wrote:
>> On 28/09/18 12:06, Lorenzo Pieralisi wrote:
>>> [+Murali, Marc]
>>>
>>> On Thu, Sep 27, 2018 at 04:44:26PM +0900, Kunihiko Hayashi wrote:
>>>> Hi Lorenzo, Gustavo,
>>>>
>>>> On Wed, 26 Sep 2018 21:31:36 +0900 <hayashi.kunihiko@socionext.com> wrote:
>>>>
>>>>> Hi Lorenzo, Gustavo,
>>>>>
>>>>> Thank you for reviewing.
>>>>>
>>>>> On Tue, 25 Sep 2018 18:53:01 +0100
>>>>> Gustavo Pimentel <gustavo.pimentel@synopsys.com> wrote:
>>>>>
>>>>>> On 25/09/2018 17:14, Lorenzo Pieralisi wrote:
>>>>>>> [+Gustavo, please have a look at INTX/MSI management]
>>>>>>>
>>>>>>> On Thu, Sep 06, 2018 at 06:40:32PM +0900, Kunihiko Hayashi wrote:
>>>>>>>> This introduces specific glue layer for UniPhier platform to support
>>>>>>>> PCIe host controller that is based on the DesignWare PCIe core, and
>>>>>>>> this driver supports Root Complex (host) mode.
>>>>>>>
>>>>>>> Please read this thread and apply it to next versions:
>>>>>>>
>>>>>>> https://urldefense.proofpoint.com/v2/url?u=https-3A__marc.info_-3Fl-3Dlinux-2Dpci-26m-3D150905742808166-26w-3D2&d=DwIBAg&c=DPL6_X_6JkXFx7AXWqB0tg&r=bkWxpLoW-f-E3EdiDCCa0_h0PicsViasSlvIpzZvPxs&m=H8UNDDUGQnQnqfWr4CBios689dJcjxu4qeTTRGulLmU&s=CgcXc_2LThyOpW-4bCriJNo9H1lzROEdy_cG9p-Y5hU&e=
>>>>>
>>>>> I also found this thread in previous linux-pci, and I think it's helpful for me.
>>>>> I'll check it carefully.
>>>>
>>>> [snip]
>>>>
>>>>>>>> +	ret = devm_request_irq(dev, pp->irq, uniphier_pcie_irq_handler,
>>>>>>>> +			       IRQF_SHARED, "pcie", priv);
>>>>>>>
>>>>>>> This is wrong, you should set-up a chained IRQ for INTX.
>>>>>>>
>>>>>>> I *think* that
>>>>>>>
>>>>>>> ks_pcie_setup_interrupts()
>>>>>>>
>>>>>>> is a good example to start with but I wonder whether it is worth
>>>>>>> generalizing the INTX approach to designware as a whole as it was
>>>>>>> done for MSIs.
>>>>>>>
>>>>>>> Thoughts ?
>>>>>>
>>>>>> From what I understood this is for legacy IRQ, right?
>>>>>
>>>>> Yes. For legacy IRQ.
>>>>>
>>>>>> Like you (Lorenzo) said there is 2 drivers (pci-keystone-dw.c and pci-dra7xx.c)
>>>>>> that uses it and can be use as a template for handling this type of interrupts.
>>>>>>
>>>>>> We can try to pass some kind of generic INTX function to the DesignWare host
>>>>>> library to handling this, but this will require some help from keystone and
>>>>>> dra7xx maintainers, since my setup doesn't have legacy IRQ HW support.
>>>>>
>>>>> Now I think it's difficult to make a template for INTX function,
>>>>> and at first, I'll try to re-write this part with reference to pci-keystone-dw.c.
>>>>
>>>> I understand that there are 2 types of interrupt and the drivers.
>>>>
>>>> One like pci-keystone-dw.c is:
>>>>
>>>>  - there are 4 interrupts for legacy,
>>>>  - invoke handlers for each interrupt, and handle the interrupt,
>>>>  - call irq_set_chained_handler_and_data() to make a chain of the interrupts
>>>>   when initializing
>>>>
>>>> The other like pci-dra7xx.c is:
>>>>
>>>>  - there is 1 IRQ for legacy as a parent,
>>>>  - check an interrupt factor register, and handle the interrupt correspond
>>>>    to the factor,
>>>>  - call request_irq() for the parent IRQ and irq_domain_add_linear() for
>>>>    the factor when initializing
>>>>
>>>> The pcie-uniphier.c is the same type as the latter (like pci-dra7xx.c).
>>>>
>>>> However, in pci-dra7xx.c, MSI and legacy IRQ share the same interrupt number,
>>>> so the same handler is called and the handler divides these IRQs.
>>>> (found in dra7xx_pcie_msi_irq_handler())
>>>>
>>>> In pcie-uniphier.c, MSI and legacy IRQ are independent.
>>>> Therefore it's necessary to prepare the handler for the legacy IRQ.
>>>>
>>>> I think that it's difficult to apply the way of pci-keystone-dw.c, and
>>>> uniphier_pcie_irq_handler() and calling devm_request_irq() are still
>>>> necessary to handle legacy IRQ.
>>>
>>> I do not think it is difficult, the difference is that keystone has
>>> 1 GIC irq line allocated per legacy IRQ, your set-up has one for
>>> all INTX.
>>>
>>> *However*, I would like some clarifications from Murali on this code
>>> in drivers/pci/controller/dwc/pci-keystone.c:
>>>
>>> static void ks_pcie_legacy_irq_handler(struct irq_desc *desc)
>>> {
>>> 	unsigned int irq = irq_desc_get_irq(desc);
>>> 	struct keystone_pcie *ks_pcie = irq_desc_get_handler_data(desc);
>>> 	struct dw_pcie *pci = ks_pcie->pci;
>>> 	struct device *dev = pci->dev;
>>> 	u32 irq_offset = irq - ks_pcie->legacy_host_irqs[0];
>>>
>>> Here the IRQ numbers are virtual IRQs, is it correct to consider
>>> the virq numbers as sequential values ? The "offset" is used to
>>> handle the PCI controller interrupt registers, so it must be a value
>>> between 0-3 IIUC.
>>
>> There is absolutely no reason why virtual interrupt numbers should be
>> contiguous. Shake the allocator hard enough, and you'll see gaps appearing.
>>
>> In general, the only thing that makes sense is to compute this offset based
>> on the hwirq which is HW-specific.
> 
> That was my understanding and why I asked, which means that keystone
> code can break (unless I read it wrong) and Murali will send me a fix as
> soon as possible please to get it right (and Kunihiko will base his
> code on this discussion).

I had cleaned up legacy interrupt handling in keystone driver [1] which was
also required for TI's AM654 Platform.

But I guess the same issue will occur in MSI interrupt handling. I'll fix that
up in the next version. Btw can you review [2] so that I can fix any other
comments that you may have.

Thanks
Kishon

[1] -> https://lore.kernel.org/patchwork/patch/989541/
[2] => https://lore.kernel.org/patchwork/cover/989487/
> 
> Lorenzo
> 
>