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

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Date:   Tue, 25 Apr 2017 14:38:39 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Ryder Lee <ryder.lee@...iatek.com>
Cc:     Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        devicetree@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        linux-mediatek@...ts.infradead.org
Subject: Re: [PATCH 1/2] PCI: mediatek: Add Mediatek PCIe host controller support

On Sun, Apr 23, 2017 at 10:19 AM, Ryder Lee <ryder.lee@...iatek.com> wrote:

> +static inline bool mtk_pcie_link_is_up(struct mtk_pcie_port *port)
> +{
> +       return !!(readl_relaxed(port->base + PCIE_LINK_STATUS) &
> +                 PCIE_PORT_LINKUP);
> +}

If this is not performance critical, please use the regular readl() instead
of readl_relaxed().

> +static bool mtk_pcie_valid_device(struct mtk_pcie *pcie,
> +                                 struct pci_bus *bus, int devfn)
> +{
> +       struct mtk_pcie_port *port;
> +       struct pci_dev *dev;
> +       struct pci_bus *pbus;
> +
> +       /* if there is no link, then there is no device */
> +       list_for_each_entry(port, &pcie->ports, list) {
> +               if (bus->number == 0 && port->index == PCI_SLOT(devfn) &&
> +                   mtk_pcie_link_is_up(port)) {
> +                       return true;
> +               } else if (bus->number != 0) {
> +                       pbus = bus;
> +                       do {
> +                               dev = pbus->self;
> +                               if (port->index == PCI_SLOT(dev->devfn) &&
> +                                   mtk_pcie_link_is_up(port)) {
> +                                       return true;
> +                               }
> +                               pbus = dev->bus;
> +                       } while (dev->bus->number != 0);
> +               }
> +       }
> +
> +       return false;
> +}




> +static int mtk_pcie_hw_rd_cfg(struct mtk_pcie *pcie, u32 bus, u32 devfn,
> +                             int where, int size, u32 *val)
> +{
> +       writel(PCIE_CONF_ADDR(where, PCI_FUNC(devfn), PCI_SLOT(devfn), bus),
> +              pcie->base + PCIE_CFG_ADDR);
> +
> +       *val = 0;
> +
> +       switch (size) {
> +       case 1:
> +               *val = readb(pcie->base + PCIE_CFG_DATA + (where & 3));
> +               break;
> +       case 2:
> +               *val = readw(pcie->base + PCIE_CFG_DATA + (where & 2));
> +               break;
> +       case 4:
> +               *val = readl(pcie->base + PCIE_CFG_DATA);
> +               break;
> +       }
> +
> +       return PCIBIOS_SUCCESSFUL;
> +}

This is a fairly standard set of read/write operations. Can you change
the pci_ops
to use pci_generic_config_read/pci_generic_config_write and an appropriate
map function instead?

> +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.

> +/*
> + * 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.

> +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?

       ARnd