Question: how can I get the real PCI address of a BAR?

Question: how can I get the real PCI address of a BAR?

[Cédric Cano]

Hi,

I'm writing a driver for a DMA engine on the PCI bus. My architecture is 
a 36-bit PowerPC (MPC85xx).

In my DMA driver, I want to configure the DMA to transfer data to/from a 
PCI device.
I get the PCI address of the device BAR with the command pci_resource_start.
This address is 36-bit but the PCI BAR of the device is 32-bit: I can't 
use the 36-bit address to run the DMA.

In kernel documentations, it's advised not to directly read the BAR.

Is there a function which provides the real PCI address i.e. the one 
stored in the BAR?

Thanks.

C. Cano

Re: Question: how can I get the real PCI address of a BAR?

[Bjorn Helgaas]

On Fri, Dec 28, 2012 at 2:36 AM, Cédric Cano <ccano@interfaceconcept.com> wrote:
> Hi,
>
> I'm writing a driver for a DMA engine on the PCI bus. My architecture is a
> 36-bit PowerPC (MPC85xx).
>
> In my DMA driver, I want to configure the DMA to transfer data to/from a PCI
> device.
> I get the PCI address of the device BAR with the command pci_resource_start.

pci_resource_start() doesn't give you a PCI bus address; it gives you
a CPU physical address.  You ioremap() that address if you want a CPU
to access the BAR MMIO space.

> This address is 36-bit but the PCI BAR of the device is 32-bit: I can't use
> the 36-bit address to run the DMA.
>
> In kernel documentations, it's advised not to directly read the BAR.
>
> Is there a function which provides the real PCI address i.e. the one stored
> in the BAR?

You can use pcibios_resource_to_bus() to convert the CPU physical
address from the pci_dev.resource[] back to a PCI bus address.
sym_iomap_device() does something similar to what you're asking about.

Bjorn

Re: Question: how can I get the real PCI address of a BAR?

[Cédric Cano]

Hi,

pcibios_resource_to_bus() does  what I need.

Thanks.

Le 30/12/2012 20:46, Bjorn Helgaas a écrit :
> On Fri, Dec 28, 2012 at 2:36 AM, Cédric Cano <ccano@interfaceconcept.com> wrote:
>> Hi,
>>
>> I'm writing a driver for a DMA engine on the PCI bus. My architecture is a
>> 36-bit PowerPC (MPC85xx).
>>
>> In my DMA driver, I want to configure the DMA to transfer data to/from a PCI
>> device.
>> I get the PCI address of the device BAR with the command pci_resource_start.
> pci_resource_start() doesn't give you a PCI bus address; it gives you
> a CPU physical address.  You ioremap() that address if you want a CPU
> to access the BAR MMIO space.
>
>> This address is 36-bit but the PCI BAR of the device is 32-bit: I can't use
>> the 36-bit address to run the DMA.
>>
>> In kernel documentations, it's advised not to directly read the BAR.
>>
>> Is there a function which provides the real PCI address i.e. the one stored
>> in the BAR?
> You can use pcibios_resource_to_bus() to convert the CPU physical
> address from the pci_dev.resource[] back to a PCI bus address.
> sym_iomap_device() does something similar to what you're asking about.
>
> Bjorn
>