linux-kernel - Re: [PATCH 2/2] PCI: mvebu: add support for orion5x

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Message-ID: <CAK8P3a042yoLR0eqt4Bm0KH4X9SJhUsjKDh1S9M+MF6mU1mPNw@mail.gmail.com>
Date:   Tue, 19 Jul 2022 10:05:28 +0200
From:   Arnd Bergmann <arnd@...db.de>
To:     Mauri Sandberg <maukka@....kapsi.fi>
Cc:     linux-pci <linux-pci@...r.kernel.org>,
        DTML <devicetree@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Andrew Lunn <andrew@...n.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Gregory CLEMENT <gregory.clement@...tlin.com>,
        Russell King - ARM Linux <linux@...linux.org.uk>,
        Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
        Pali Rohár <pali@...nel.org>
Subject: Re: [PATCH 2/2] PCI: mvebu: add support for orion5x

On Mon, Jul 18, 2022 at 10:28 PM Mauri Sandberg <maukka@....kapsi.fi> wrote:
>
> Add support for orion5x PCIe controller.
>
> There is Orion-specific errata that config space via CF8/CFC registers
> is broken. Workaround documented in errata documented (linked from above
> documentation) does not work when DMA is used and instead other
> undocumented workaround is needed which maps config space to memory
> (and therefore avoids usage of broken CF8/CFC memory mapped registers).
>
> Signed-off-by: Mauri Sandberg <maukka@....kapsi.fi>
> Cc: Pali Rohár <pali@...nel.org>

Nice job, glad you managed to figure this out!

> diff --git a/arch/arm/mach-orion5x/common.c b/arch/arm/mach-orion5x/common.c
> index 7bcb41137bbf..9d8be5ce1266 100644
> --- a/arch/arm/mach-orion5x/common.c
> +++ b/arch/arm/mach-orion5x/common.c
> @@ -231,19 +231,6 @@ void __init orion5x_init_early(void)
>
>  void orion5x_setup_wins(void)
>  {
> -       /*
> -        * The PCIe windows will no longer be statically allocated
> -        * here once Orion5x is migrated to the pci-mvebu driver.
> -        */
> -       mvebu_mbus_add_window_remap_by_id(ORION_MBUS_PCIE_IO_TARGET,
> -                                         ORION_MBUS_PCIE_IO_ATTR,
> -                                         ORION5X_PCIE_IO_PHYS_BASE,
> -                                         ORION5X_PCIE_IO_SIZE,
> -                                         ORION5X_PCIE_IO_BUS_BASE);
> -       mvebu_mbus_add_window_by_id(ORION_MBUS_PCIE_MEM_TARGET,
> -                                   ORION_MBUS_PCIE_MEM_ATTR,
> -                                   ORION5X_PCIE_MEM_PHYS_BASE,
> -                                   ORION5X_PCIE_MEM_SIZE);
>         mvebu_mbus_add_window_remap_by_id(ORION_MBUS_PCI_IO_TARGET,
>                                           ORION_MBUS_PCI_IO_ATTR,
>                                           ORION5X_PCI_IO_PHYS_BASE,

If the idea is to have the PCI_MVEBU driver only used for the DT based orion5x
machines, but not the legacy board files, I suspect this breaks the legacy
pci driver, unless you move the mbus configuration into the pcie_setup()
function.

> +/* Relevant only for Orion-1/Orion-NAS */
> +#define ORION5X_PCIE_WA_PHYS_BASE      0xf0000000
> +#define ORION5X_PCIE_WA_VIRT_BASE      IOMEM(0xfd000000)

You should not need to hardcode these here. The ORION5X_PCIE_WA_PHYS_BASE
should already be part of the DT binding. There is little practical difference
here, but I see no value in taking the shortcut here either.

For the ORION5X_PCIE_WA_VIRT_BASE, you rely on this to match the
definition in arch/arm/mach-orion5x/common.c, and this is rather fragile.

Instead, please use ioremap() to create a mapping at runtime. The ioremap()
implementation on ARM is smart enough to reuse the address from the static
mapping in common.c, but will also keep working if that should go away.

> +#define ORION5X_PCIE_WA_SIZE           SZ_16M
> +#define ORION_MBUS_PCIE_WA_TARGET      0x04
> +#define ORION_MBUS_PCIE_WA_ATTR                0x79
> +
> +static int mvebu_pcie_child_rd_conf_wa(struct pci_bus *bus, u32 devfn, int where, int size, u32 *val)
> +{
> +       struct mvebu_pcie *pcie = bus->sysdata;
> +       struct mvebu_pcie_port *port;
> +
> +       port = mvebu_pcie_find_port(pcie, bus, devfn);
> +       if (!port)
> +               return PCIBIOS_DEVICE_NOT_FOUND;
> +
> +       if (!mvebu_pcie_link_up(port))
> +               return PCIBIOS_DEVICE_NOT_FOUND;
> +
> +       /*
> +        * We only support access to the non-extended configuration
> +        * space when using the WA access method (or we would have to
> +        * sacrifice 256M of CPU virtual address space.)
> +        */
> +       if (where >= 0x100) {
> +               *val = 0xffffffff;
> +               return PCIBIOS_DEVICE_NOT_FOUND;
> +       }
> +
> +       return orion_pcie_rd_conf_wa(ORION5X_PCIE_WA_VIRT_BASE, bus, devfn, where, size, val);
> +}
> +

This is probably good enough here, though I think you could also use
the trick from drivers/pci/ecam.c and map each bus at a time.

      Arnd