linux-kernel - Re: [PATCH 1/2] PCI: mediatek: Add Mediatek PCIe host controller support

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Message-ID: <1493347608.29314.56.camel@mtkswgap22>
Date:   Fri, 28 Apr 2017 10:46:48 +0800
From:   Ryder Lee <ryder.lee@...iatek.com>
To:     Arnd Bergmann <arnd@...db.de>
CC:     <devicetree@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        Rob Herring <robh+dt@...nel.org>,
        <linux-mediatek@...ts.infradead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/2] PCI: mediatek: Add Mediatek PCIe host controller
 support

Hi,

On Thu, 2017-04-27 at 20:55 +0200, Arnd Bergmann wrote:
> On Wed, Apr 26, 2017 at 10:10 AM, Ryder Lee <ryder.lee@...iatek.com> wrote:
> > On Tue, 2017-04-25 at 14:38 +0200, Arnd Bergmann wrote:
> >> On Sun, Apr 23, 2017 at 10:19 AM, Ryder Lee <ryder.lee@...iatek.com> wrote:
> 
> >> > +static int mtk_pcie_enable_ports(struct mtk_pcie *pcie)
> >> > +{
> >> > +       struct device *dev = pcie->dev;
> >> > +       struct mtk_pcie_port *port, *tmp;
> >> > +       int err, linkup = 0;
> >> > +
> >> > +       list_for_each_entry_safe(port, tmp, &pcie->ports, list) {
> >> > +               err = clk_prepare_enable(port->sys_ck);
> >> > +               if (err) {
> >> > +                       dev_err(dev, "failed to enable port%d clock\n",
> >> > +                               port->index);
> >> > +                       continue;
> >> > +               }
> >> > +
> >> > +               /* assert RC */
> >> > +               reset_control_assert(port->reset);
> >> > +               /* de-assert RC */
> >> > +               reset_control_deassert(port->reset);
> >> > +
> >> > +               /* power on PHY */
> >> > +               err = phy_power_on(port->phy);
> >> > +               if (err) {
> >> > +                       dev_err(dev, "failed to power on port%d phy\n",
> >> > +                               port->index);
> >> > +                       goto err_phy_on;
> >> > +               }
> >> > +
> >> > +               mtk_pcie_assert_ports(port);
> >> > +
> >>
> >> Similar to the comment I had for the binding, I wonder if it would be
> >> better to keep all the information about the ports in one place and
> >> then just deal with it at the root level.
> >>
> >> Alternatively, we could decide to standardize on the properties
> >> you have added to the pcie port node, but then I would handle
> >> them in the pcieport driver rather than in the host bridge driver.
> >
> > Sorry, I'm not sure what you want me to do here.
> >
> > I could move all clock operation in root level. But we need to keep the
> > reset and PHY operation sequence in the loop, In addition, we could
> > easily free resources if ports link fail.
> >
> > How about moving this function to mtk_pcie_parse_and_add_res()?
> 
> That could work, please try it out and see if the code gets better or
> worse. This may depend on what we end up doing with the DT
> properties.

I will try it on next version, and we can continue our discussion on
that series.

> >> > +/*
> >> > + * This IP lacks interrupt status register to check or map INTx from
> >> > + * different devices at the same time.
> >> > + */
> >> > +static int __init mtk_pcie_map_irq(const struct pci_dev *dev, u8 slot, u8 pin)
> >> > +{
> >> > +       struct mtk_pcie *pcie = dev->bus->sysdata;
> >> > +       struct mtk_pcie_port *port;
> >> > +
> >> > +       list_for_each_entry(port, &pcie->ports, list)
> >> > +               if (port->index == slot)
> >> > +                       return port->irq;
> >> > +
> >> > +       return -1;
> >> > +}
> >>
> >> This looks odd, what is it needed for specifically? It looks like
> >> it's broken for devices behind bridges, and the interrupt mapping
> >> should normally come from the interrupt-map property, without
> >> the need for a driver specific map_irq override.
> >
> > Our hardware just has a GIC for each port and lacks interrupt status for
> > host driver to distinguish INTx. So I return port IRQ here.
> 
> You should still be able to express this with standard interrupt-map
> DT property, without having to resort to your own map_irq
> callback handler.
> 
> In the interrupt-map-mask, you can ignore the interrupt line
> only list the devfn of the root ports for each entry.

Okay, I will fix it.

> >> > +static int mtk_pcie_register_ports(struct mtk_pcie *pcie)
> >> > +{
> >> > +       struct pci_bus *bus, *child;
> >> > +
> >> > +       bus = pci_scan_root_bus(pcie->dev, 0, &mtk_pcie_ops, pcie,
> >> > +                               &pcie->resources);
> >>
> >> Can you use the new pci_register_host_bridge() method instead of
> >> pci_scan_root_bus() here?
> >
> > May I know what's difference between pci_scan_root_bus() and using
> > pci_register_host_bridge() directly? What situation should we use it?
> > It seems that just tegra use this new method currently.
> 
> We introduced the new function for tegra for now, in the long run
> I would hope we can convert all other drivers to it as well, to make it
> easier to add further parameters.
> 
> The new function also has a cleaner way of dealing with the memory
> allocations, similar to how other subsystems work.

Sounds good. I will change to use that.

Thanks!