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

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Date:   Mon, 9 Jan 2017 22:45:59 +0100
From:   "Rafael J. Wysocki" <rafael@...nel.org>
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>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        jorn Helgaas <bhelgaas@...gle.com>,
        Dongdong Liu <liudongdong3@...wei.com>,
        Gabriele Paoloni <gabriele.paoloni@...wei.com>,
        xuwei5@...ilicon.com,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Linux PCI <linux-pci@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] ACPI/PCI: Fix bus range comparation in pci_mcfg_lookup

On Mon, Jan 9, 2017 at 4:39 AM, Zhou Wang <wangzhou1@...ilicon.com> wrote:
> On 2017/1/4 15:00, Zhou Wang wrote:
>> 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.
>>
>> Signed-off-by: Zhou Wang <wangzhou1@...ilicon.com>
>> Reviewed-by: Tomasz Nowicki <tn@...ihalf.com>
>> Acked-by: Lorenzo Pieralisi <lorenzo.pieralisi@....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 a6a4cea..2944353 100644
>> --- a/drivers/acpi/pci_mcfg.c
>> +++ b/drivers/acpi/pci_mcfg.c
>> @@ -195,11 +195,10 @@ int pci_mcfg_lookup(struct acpi_pci_root *root, struct resource *cfgres,
>>               goto skip_lookup;
>>
>>       /*
>> -      * 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) {
>>                       root->mcfg_addr = e->addr;
>>               }
>>
>
> Hi Rafael,
>
> Could you please look into this patch if you have time?

Well, it makes sense to me, but this is PCI, so Bjorn has to decide here.

Thanks,
Rafael