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

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Date:   Thu, 27 Sep 2018 16:44:26 +0900
From:   Kunihiko Hayashi <hayashi.kunihiko@...ionext.com>
To:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Gustavo Pimentel <gustavo.pimentel@...opsys.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Masahiro Yamada <yamada.masahiro@...ionext.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Masami Hiramatsu <masami.hiramatsu@...aro.org>,
        Jassi Brar <jaswinder.singh@...aro.org>
Subject: Re: [PATCH v2 2/2] PCI: controller: dwc: add UniPhier PCIe host controller support

Hi Lorenzo, Gustavo,

On Wed, 26 Sep 2018 21:31:36 +0900 <hayashi.kunihiko@...ionext.com> wrote:

> Hi Lorenzo, Gustavo,
> 
> Thank you for reviewing.
> 
> On Tue, 25 Sep 2018 18:53:01 +0100
> Gustavo Pimentel <gustavo.pimentel@...opsys.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.

Thank you,

---
Best Regards,
Kunihiko Hayashi