linux-kernel - Re: [PATCH] PCI: controller: dwc: Make PCI

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Date:   Thu, 6 Dec 2018 20:55:13 -0800
From:   Andrey Smirnov <andrew.smirnov@...il.com>
To:     Lucas Stach <l.stach@...gutronix.de>
Cc:     linux-pci@...r.kernel.org, Bjorn Helgaas <bhelgaas@...gle.com>,
        Chris Healy <cphealy@...il.com>,
        Leonard Crestez <leonard.crestez@....com>,
        Dong Aisheng <aisheng.dong@....com>,
        Richard Zhu <hongxing.zhu@....com>, linux-imx@....com,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] PCI: controller: dwc: Make PCI_IMX6 depend on PCIEPORTBUS

On Thu, Dec 6, 2018 at 2:28 AM Lucas Stach <l.stach@...gutronix.de> wrote:
>
> Am Mittwoch, den 05.12.2018, 23:45 -0800 schrieb Andrey Smirnov:
> > Building a kernel with CONFIG_PCI_IMX6=y, but CONFIG_PCIEPORTBUS=n
> > produces a system where built-in PCIE bridge (16c3:abcd) isn't bound
> > to pcieport driver. This, in turn, results in a PCIE bus that is
> > capable of enumerating attached PCIE device, but lacks functional
> > interrupt support.
>
> This is odd. AFAIK PCI port services are a totally optional thing and
> them being absent should not lead to a non-functional PCI bus. So I
> would really like to see some deeper analysis what is going on here.
>

AFAICT, this is due to pcieport driver enabling MSI of the bridge
device (16c3:abcd) via pcie_port_device_register() ->
pcie_init_service_irqs() -> pcie_port_enable_irq_vec() -> etc.

I did an experiment on a i.MX8MQ/PCIE -> i210 setup I have: I disabled
CONFIG_PCIEPORTBUS and hacked igb_main.c enough to make the i210
driver believe it should fall back onto legacy interrupts. Even
without pcieport present in the system, i210 worked as expected via
legacy interrupts, which seems to collaborate my conjecture above.

Thanks,
Andrey Smirnov