linux-kernel - Re: [PATCH] ARM: Gemini: Add support for PCI BUS

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Date:	Sun, 28 Nov 2010 20:56:17 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	linux-arm-kernel@...ts.infradead.org
Cc:	Hans Ulli Kroll <ulli.kroll@...glemail.com>,
	Russell King <linux@....linux.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] ARM: Gemini: Add support for PCI BUS

On Saturday 27 November 2010 13:24:35 Hans Ulli Kroll wrote:
> +#define PCI_IOSIZE_REG         (IO_ADDRESS(GEMINI_PCI_IO_BASE))
> +#define PCI_PROT_REG           (IO_ADDRESS(GEMINI_PCI_IO_BASE) + 0x04)
> +#define PCI_CTRL_REG           (IO_ADDRESS(GEMINI_PCI_IO_BASE) + 0x08)
> +#define PCI_SOFTRST_REG                (IO_ADDRESS(GEMINI_PCI_IO_BASE) + 0x10)
> +#define PCI_CONFIG_REG         (IO_ADDRESS(GEMINI_PCI_IO_BASE) + 0x28)
> +#define PCI_DATA_REG           (IO_ADDRESS(GEMINI_PCI_IO_BASE) + 0x2C)

If you use the virtual address of the mapping instead of
GEMINI_PCI_IO_BASE, you don't need to repeat the IO_ADDRESS()
macro everywhere. I have a patch that gets rid of all the
conflicting definitions of this macro because it breaks
a multi-platform build once we get there. 

> +static DEFINE_SPINLOCK(gemini_pci_lock);
> +
> +static struct resource gemini_pci_resource_io = {
> +       .name   = "PCI I/O Space",
> +       .start  = IO_ADDRESS(GEMINI_PCI_IO_BASE),
> +       .end    = IO_ADDRESS(GEMINI_PCI_IO_BASE) + SZ_1M - 1,
> +       .flags  = IORESOURCE_IO,
> +};
> +

This looks wrong in multiple ways:

* resources are physical addresses, not virtual addresses
* GEMINI_PCI_IO_BASE is an address in memory space, so it
  needs to be IORESOURCE_MEM, not IORESOURCE_IO. You can
  also register the IORESOURCE_IO resource, but that would
  be .start=PCIBIOS_MIN_IO, .end=IO_SPACE_LIMIT.
* IO_SPACE_LIMIT is larger than the I/O window, which can
  cause overflows. Setting it to 0xffff is generally enough.

> +       spin_lock_irqsave(&gemini_pci_lock, irq_flags);
> +
> +       __raw_writel(PCI_CONF_BUS(bus->number) |
> +                       PCI_CONF_DEVICE(PCI_SLOT(fn)) |
> +                       PCI_CONF_FUNCTION(PCI_FUNC(fn)) |
> +                       PCI_CONF_WHERE(config) |
> +                       PCI_CONF_ENABLE,
> +                       PCI_CONFIG_REG);
> +
> +       switch (size) {
> +       case 4:
> +               __raw_writel(value, PCI_DATA_REG);
> +               break;
> +       case 2:
> +               __raw_writew(value, PCI_DATA_REG + (config & 3));
> +               break;
> +       case 1:
> +               __raw_writeb(value, PCI_DATA_REG + (config & 3));
> +               break;
> +       default:
> +               ret = PCIBIOS_BAD_REGISTER_NUMBER;
> +       }
> +
> +       spin_unlock_irqrestore(&gemini_pci_lock, irq_flags);

The I/O ordering is probably not what you think it is.
There is no ordering guarantee between __raw_writel and
spin_lock/spin_unlock, so you really should be using
readl/writel.

Note that the pci_ops are called under another spinlock, so
you also don't need to take gemini_pci_lock here.

	Arnd
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