Re: [RFC net-next 1/4] net: Allow non parent devices to be used for ZC DMA

[Pavel Begunkov <asml.silence@gmail.com>]

On 7/4/25 14:11, Dragos Tatulea wrote:
> On Thu, Jul 03, 2025 at 01:58:50PM +0200, Parav Pandit wrote:
>>
>>> From: Jakub Kicinski <kuba@kernel.org>
>>> Sent: 03 July 2025 02:23 AM
...>> In an offline discussion, Dragos mentioned that io_uring already
>> operates at the queue level, may be some ideas can be picked up
>> from io_uring?
> The problem for devmem is that the device based API is already set in
> stone so not sure how we can change this. Maybe Mina can chime in.
> 
> To sum the conversation up, there are 2 imperfect and overlapping
> solutions:
> 
> 1) For the common case of having a single PCI device per netdev, going one
>     parent up if the parent device is not DMA capable would be a good
>     starting point.
> 
> 2) For multi-PF netdev [0], a per-queue get_dma_dev() op would be ideal
>     as it provides the right PF device for the given queue. io_uring
>     could use this but devmem can't. Devmem could use 1. but the
>     driver has to detect and block the multi PF case.
> 
> I think we need both. Either that or a netdev op with an optional queue
> parameter. Any thoughts?

No objection from zcrx for either approach, but it sounds like a good
idea to have something simple for 1) sooner than later, and perhaps
marked as a fix.

-- 
Pavel Begunkov