netdev - Re: [PATCH net-next 2/3] net: page_pool: add the possibility to sync DMA memory for non-coherent devices

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Date:   Fri, 15 Nov 2019 18:53:31 +0200
From:   Lorenzo Bianconi <lorenzo@...nel.org>
To:     Jonathan Lemon <jonathan.lemon@...il.com>
Cc:     Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Lorenzo Bianconi <lorenzo.bianconi@...hat.com>,
        Jesper Dangaard Brouer <brouer@...hat.com>,
        netdev@...r.kernel.org, davem@...emloft.net,
        thomas.petazzoni@...tlin.com, matteo.croce@...hat.com
Subject: Re: [PATCH net-next 2/3] net: page_pool: add the possibility to sync
 DMA memory for non-coherent devices

[...]

> > > > 
> > > > Okay, then i guess the flag is a better fit for this.
> > > > The only difference would be that the sync semantics will be
> > > > done on 'per
> > > > packet' basis,  instead of 'per pool', but that should be fine
> > > > for our cases.
> > > 
> > > Ack, fine for me.
> > > Do you think when checking for PP_FLAG_DMA_SYNC_DEV we should even
> > > verify
> > > PP_FLAG_DMA_MAP? Something like:
> > > 
> > > if ((pool->p.flags & (PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV)) ==
> > >     (PP_FLAG_DMA_MAP | PP_FLAG_DMA_SYNC_DEV))
> > > 	page_pool_dma_sync_for_device();
> > > 
> > > Regards,
> > > Lorenzo
> > 
> > I think it's better to do the check once on the pool registration and
> > maybe
> > refuse to allocate the pool? Syncing without mapping doesn't really make
> > sense
> 
> +1.

ack, will post v3 soon.

Regards,
Lorenzo

> -- 
> Jonathan

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