Re: Regarding port numbers assigned by DPDK for PCI devices

[Ferruh Yigit <ferruh.yigit@amd.com>]

On 7/30/2024 6:36 AM, Prashant Upadhyaya wrote:
> 
> 
> 
> On Mon, 29 Jul 2024 at 23:13, Dmitry Kozlyuk <dmitry.kozliuk@gmail.com
> <mailto:dmitry.kozliuk@gmail.com>> wrote:
> 
>     2024-07-29 22:18 (UTC+0530), Prashant Upadhyaya:
>     > Hi,
>     >
>     > I have 4 ethernet interfaces available as PCI devices.
>     > The PCI addresses are known.
>     > When I start my DPDK application, it starts up properly and
>     assigns the
>     > port numbers to them as 0, 1, 2, 3 expectedly.
>     >
>     > However, is there a way I can force that a particular PCI address
>     should be
>     > identified as port 0 by DPDK, another one as port 1 and so forth ?
>     > Does passing the arguments like -a <address1> -a <address2> to
>     rte_eal_init
>     > ensure that, or is there any other way, or is there no way ?
>     >
>     > I am on 24.03
>     >
>     > Regards
>     > -Prashant
> 
>     Hi,
> 
>     Why do you need specific port numbers assigned to devices?
> 
>     If you're going to use devices for different purposes,
>     you'd better have an application-level configuration
>     to specify PCI addresses to use for each purpose.
>     Iterate devices to match the address and find the port number.
> 
>     It is also possible to disable automatic probing with "-a 0:0.0",
>     then to use rte_dev_probe() + rte_dev_event_callback_register()
>     to add devices and to get their port numbers.
>     However, this API, strictly speaking, does not guarantee
>     that the numbers will be assigned sequentially.
>     One advantage of using hot-plug is that you can build devargs
>     from within the application (or from configuration).
> 
>     Refer to "rte_dev.h" in any case.
>     Multiple "-a" don't work the way you've described.
> 
> 
> 
> Thanks Dmitry. Ok, so if I have the port number with me, and I know it
> corresponds to a PCI device, how do I find out the PCI address of this
> device corresponding to this port number. I believe I can
> do rte_eth_dev_info_get to get the struct rte_eth_dev_info and from
> there the rte_device, but what after that ? I saw some references
> to RTE_DEV_TO_PCI but that macro isn't available for compilation after
> DPDK is installed as it is an internal header file and thus not a macro
> for application usage and wouldn't compile at application level.
> 
> 

Hi Prashant,

For PCI bus, most of the times ethdev device name is PCI ID, so you can
use 'rte_eth_dev_get_name_by_port(port_id, name)' API to get PCI ID for
port.

But there are cases this is not true, like single PCI ID creates
multiple ethdev etc... for this case, PCI ID can be get from device name:
rte_eth_dev_info_get(port_id, *dev_info)
name = rte_dev_name(dev_info->device)