linux-kernel - Re: Purpose of PCI address in ranges property

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Message-ID: <dc0416ae-d28b-0d9a-cfbd-2bd98abc69d0@gmail.com>
Date:   Thu, 23 Mar 2017 08:29:25 +0530
From:   valmiki <valmikibow@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        Bjorn Helgaas <helgaas@...nel.org>,
        Marc Zyngier <marc.zyngier@....com>
Subject: Re: Purpose of PCI address in ranges property

On 3/20/2017 3:15 AM, Arnd Bergmann wrote:
> On Sun, Mar 19, 2017 at 3:14 PM, valmiki <valmikibow@...il.com> wrote:
>> Hi,
>>
>> When ranges property is being parsed using of_pci_get_host_bridge_resources,
>> the pci address is being used for
>> calculating the offset for pci_add_resource_offset.
>>
>> What is this offset for ?
>>
>> So the cpu address is being used for programming memory base and limit
>> registers ?
>
> Linux IORESOURCE_MEM resources are defined in terms of CPU addresses,
> while PCI config space BAR registers are programmed with bus addresses.
> These are often the same, but on some machines they are not, which results
> in an offset that has to be used when accessing the BARs.
>
Thanks Arnd. So mem base and limit registers of RP are programmed with 
CPU addresses,
and EP BARs are programmed with PCI bus addresses ?
So when will this offset be used, only when RP assigns BAR's to RP ?

Regards,
Valmiki