linux-kernel - Re: [PATCH 4/5]PCI: x86 MMCONFIG: introduce pcibios_fix_bus

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Date:	Wed, 19 Dec 2007 15:10:32 -0800
From:	Greg KH <gregkh@...e.de>
To:	tcamuso@...hat.com
Cc:	linux-kernel@...r.kernel.org, linux-pci@...ey.karlin.mff.cuni.cz,
	prarit@...hat.com
Subject: Re: [PATCH 4/5]PCI: x86 MMCONFIG: introduce pcibios_fix_bus_scan()

On Wed, Dec 19, 2007 at 05:18:06PM -0500, tcamuso@...hat.com wrote:
> commit ab28e1157e970f711c8451b66b3f940ec092db9d
> Author: Tony Camuso <tony.camuso@...com>
> Date:   Wed Dec 19 15:51:48 2007 -0500
> 
>     Introduces the x86 arch-specific routine that will determine whether
>     a device responds correctly to MMCONFIG accesses. This routine is
>     given the generic name pcibios_fix_bus_scan_quirk()
>     
>     The comment at the top of the routine explains its logic.
>     
>     Signed-off-by: Tony Camuso tony.camuso@...com
> 
> diff --git a/arch/x86/pci/common.c b/arch/x86/pci/common.c
> index 8627463..9b1742d 100644
> --- a/arch/x86/pci/common.c
> +++ b/arch/x86/pci/common.c
> @@ -525,3 +525,64 @@ struct pci_bus *pci_scan_bus_with_sysdata(int busno)
>  
>  	return bus;
>  }
> +
> +/**
> + * This routine traps devices not correctly responding to MMCONFIG access.
> + * For each device on the current bus, compare a mmconf read of the
> + * vendor/device dword with a legacy PCI config read. If they're not the same,
> + * the bus serving this device must use legacy PCI config accesses instead of
> + * mmconf, as must all buses descending from this bus.
> + */
> +
> +#define CHECK_MMCFG_STR_1 \
> +	"PCI: Device at %04x:%02x.%02x.%x is not MMCONFIG compliant.\n"
> +#define CHECK_MMCFG_STR_2 \
> +	"PCI: Bus %04x:%02x and its descendents cannot use MMCONFIG.\n"

Why define these if they are only used in one place?

Also, as you use dev_info(), I think you are duplicating some of the
information in the resulting printk(), right?

> +
> +void __devinit pcibios_fix_bus_scan_quirk(struct pci_bus *bus)
> +{
> +	int devfn;
> +	int fail;
> +	int found_nommconf_dev = 0;
> +	static int advised;
> +	u32 mcfg_vendev;
> +	u32 arch_vendev;
> +	struct pci_ops *save_ops = bus->ops;
> +
> +	if (bus->parent != NULL)
> +		if (bus->parent->ops == &pci_legacy_ops)
> +			return;
> +
> +	if (!advised) {
> +		pr_info("PCI: If a device isn't working, try \"pci=nommconf\". "
> +			"If that helps, please post a report.\n");

Post a report where?  Who is going to handle these reports?

The last time someone put a line like this in the kernel, I got a ton of
email and didn't know what to do with it.  If you really are trusting of
this patch, please put your email address in this printk(), so that you
can properly handle the resulting reports.  I sure don't want to :)

> +		advised = 1;
> +	}
> +	pr_debug("PCI: Checking bus %04x:%02x for MMCONFIG compliance.\n",
> +		 pci_domain_nr(bus), bus->number);
> +
> +	for (devfn = 0; devfn < 256; devfn++) {
> +		bus->ops = &pci_legacy_ops;
> +		fail = (pci_bus_read_config_dword(bus, devfn, PCI_VENDOR_ID,
> +						  &arch_vendev));

What's with the extra () around the function?

> +		if ((arch_vendev == 0xFFFFFFFF) || (arch_vendev == 0) || fail)
> +			continue;
> +
> +		bus->ops = save_ops;	/* Restore to original value */
> +		pci_bus_read_config_dword(bus, devfn, PCI_VENDOR_ID,
> +					  &mcfg_vendev);
> +		if (mcfg_vendev != arch_vendev) {
> +			found_nommconf_dev = 1;
> +			break;
> +		}
> +	}
> +
> +	if (found_nommconf_dev) {
> +		pr_info(CHECK_MMCFG_STR_1, pci_domain_nr(bus), bus->number,
> +			PCI_SLOT(devfn), PCI_FUNC(devfn));
> +		pr_info(CHECK_MMCFG_STR_2, pci_domain_nr(bus), bus->number);
> +		bus->ops = &pci_legacy_ops;	/* Use Legace PCI Config */

Spelling check for your comments :)

thanks,

greg k-h
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