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

Lorenzo Pieralisi
2018-09-28T11:06:52Z

[+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.

I would appreciated a detailed explanation of keystone legacy IRQ
handling so that we can eventually try to replicate it and generalize
it.

Lorenzo

[...]

chained_irq_enter(chip, desc);
ks_dw_pcie_handle_legacy_irq(ks_pcie, irq_offset);
chained_irq_exit(chip, desc);
}