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

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Date:	Mon, 29 Nov 2010 18:05:07 +0200
From:	Paulius Zaleckas <paulius.zaleckas@...il.com>
To:	Arnd Bergmann <arnd@...db.de>
CC:	linux-arm-kernel@...ts.infradead.org,
	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 11/28/2010 09:56 PM, Arnd Bergmann wrote:
> 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.

No he really should NOT use readl/writel. The ONLY difference
between readl/writel and __raw_readl/__raw_writel is endianess
conversion. __raw_*l is not doing it. Which to use depend only
on HW.

> 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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