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

[Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>]

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.

More to it, AFAIK the list of HW irqs in the PCI host bridge controller
"interrupts" property is not necessarily a sequential list of numbers
either.

If I understand how these bindings/code works, the PCI INTX legacy IRQs
are mapped to IRQ lines {0,1,2,3} of the PCI host bridge interrupt
controller through the "interrupt-map" property.

Those IRQ lines are cascaded to the GIC through the HW irq in the
PCI host controller "interrupts" property:

IRQ line 0 <-> first cell of "interrupts" property
IRQ line 1 <-> second cell of "interrupts" property

and so forth.

I am not sure there is anything formal defining this behaviour other
than implicit expectactions.

@Murali: can you clarify please ?

Lorenzo