Re: [PATCH net-next v1] page_pool: check for dma_sync_size earlier

[Furong Xu]

Hi Jakub,

On Fri, 11 Oct 2024 16:55:34 +0800, Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote:

> On 2024/10/11 14:31, Furong Xu wrote:
> > Hi Ilias,
> > 
> > On Fri, 11 Oct 2024 08:06:04 +0300, Ilias Apalodimas <ilias.apalodimas@xxxxxxxxxx> wrote:
> >   
> >> Hi Furong,
> >>
> >> On Fri, 11 Oct 2024 at 05:15, Furong Xu <0x1207@xxxxxxxxx> wrote:  
> >>>
> >>> On Thu, 10 Oct 2024 19:53:39 +0800, Yunsheng Lin <linyunsheng@xxxxxxxxxx> wrote:
> >>>    
> >>>> Is there any reason that those drivers not to unset the PP_FLAG_DMA_SYNC_DEV
> >>>> when calling page_pool_create()?
> >>>> Does it only need dma sync for some cases and not need dma sync for other
> >>>> cases? if so, why not do the dma sync in the driver instead?    
> >>>
> >>> The answer is in this commit:
> >>> https://git.kernel.org/netdev/net/c/5546da79e6cc    
> >>
> >> I am not sure I am following. Where does the stmmac driver call a sync
> >> with len 0?  
> > For now, only drivers/net/ethernet/freescale/fec_main.c does.
> > And stmmac driver does not yet, but I will send another patch to make it call sync with
> > len 0. This is a proper fix as Jakub Kicinski suggested.  
> 
> In order to support the above use case, it seems there might be two
> options here:
> 1. Driver calls page_pool_create() without PP_FLAG_DMA_SYNC_DEV and
>    handle the dma sync itself.
> 2. Page_pool may provides a non-dma-sync version of page_pool_put_page()
>    API even when Driver calls page_pool_create() with PP_FLAG_DMA_SYNC_DEV.
> 
> Maybe option 2 is better one in the longer term as it may provide some
> flexibility for the user and enable removing of the DMA_SYNC_DEV in the
> future?

What is your opinion about this?
Thanks.