linux-kernel - Re: [RFC PATCH] ACPI/PCI: Fix bus range comparation in pci_mcfg

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Message-ID: <20170103120021.GC7145@red-moon>
Date:   Tue, 3 Jan 2017 12:00:21 +0000
From:   Lorenzo Pieralisi <lorenzo.pieralisi@....com>
To:     Zhou Wang <wangzhou1@...ilicon.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Len Brown <lenb@...nel.org>, Tomasz Nowicki <tn@...ihalf.com>,
        Jayachandran C <jchandra@...adcom.com>,
        jorn Helgaas <bhelgaas@...gle.com>, liudongdong3@...wei.com,
        gabriele.paoloni@...wei.com, linux-acpi@...r.kernel.org,
        linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH] ACPI/PCI: Fix bus range comparation in
 pci_mcfg_lookup

On Thu, Dec 22, 2016 at 05:07:43PM +0800, Zhou Wang wrote:
> Multiple PCIe host bridges may exists in one PCIe segment. So bus range for each
> host bridge should be in the coverage of bus range of related PCIe segment.
> 
> This patch will support this kind of scenario:
> 
> MCFG:
> 	bus range: 0x00~0xff.
> 	segment: 0.
> DSDT:
> 	host bridge 1:
> 		bus range: 0x00~0x1f.
> 		segment: 0.
> 	host bridge 2:
> 		bus range: 0x20~0x4f.
> 		segment: 0.

"The configuration data provided by an MCFG region (ie PCI segment and
bus range) may span multiple host bridges.

Current code in pci_mcfg_lookup() carries out an exact match of host
bridge bus range start value against the MCFG region(s) bus range start
value which would cause configurations like the following:

MCFG region:
	bus range: 0x00~0xff.
	segment: 0.

PCI host bridges configuration (segment numbers and bus ranges):
	host bridge 1:
		bus range: 0x00~0x1f.
		segment: 0.
	host bridge 2:
		bus range: 0x20~0x4f.
		segment: 0.

to fail, in that the bus range start value for host bridge 2 does
not match the bus range start value of the respective MCFG region.

Relax the bus range check in pci_mcfg_lookup() to cater for
PCI configurations with multiple host bridges sharing the same
MCFG region."

Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@....com>

> Signed-off-by: Zhou Wang <wangzhou1@...ilicon.com>
> ---
>  drivers/acpi/pci_mcfg.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/acpi/pci_mcfg.c b/drivers/acpi/pci_mcfg.c
> index b5b376e..46a3e32 100644
> --- a/drivers/acpi/pci_mcfg.c
> +++ b/drivers/acpi/pci_mcfg.c
> @@ -40,11 +40,10 @@ phys_addr_t pci_mcfg_lookup(u16 seg, struct resource *bus_res)
>  	struct mcfg_entry *e;
>  
>  	/*
> -	 * We expect exact match, unless MCFG entry end bus covers more than
> -	 * specified by caller.
> +	 * We expect the range in bus_res in the coverage of MCFG bus range.
>  	 */
>  	list_for_each_entry(e, &pci_mcfg_list, list) {
> -		if (e->segment == seg && e->bus_start == bus_res->start &&
> +		if (e->segment == seg && e->bus_start <= bus_res->start &&
>  		    e->bus_end >= bus_res->end)
>  			return e->addr;
>  	}
> -- 
> 1.9.1
>