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Date:   Fri, 28 Sep 2018 12:06:40 +0100
From:   Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
To:     Kunihiko Hayashi <hayashi.kunihiko@socionext.com>
Cc:     Gustavo Pimentel <gustavo.pimentel@synopsys.com>,
        Bjorn Helgaas <bhelgaas@google.com>,
        Rob Herring <robh+dt@kernel.org>,
        Mark Rutland <mark.rutland@arm.com>,
        Masahiro Yamada <yamada.masahiro@socionext.com>,
        "linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
        "devicetree@vger.kernel.org" <devicetree@vger.kernel.org>,
        "linux-arm-kernel@lists.infradead.org" 
        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>,
        Masami Hiramatsu <masami.hiramatsu@linaro.org>,
        Jassi Brar <jaswinder.singh@linaro.org>,
        Murali Karicheri <m-karicheri2@ti.com>, marc.zyngier@arm.com
Subject: Re: [PATCH v2 2/2] PCI: controller: dwc: add UniPhier PCIe host
 controller support
Message-ID: <20180928110640.GA18840@e107981-ln.cambridge.arm.com>
References: <b869b273-e681-0b8c-52f5-6e02f9de5485@synopsys.com>
 <20180926213135.A4B4.4A936039@socionext.com>
 <20180927164426.ECD6.4A936039@socionext.com>
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[+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);
}