Re: [PATCH] net: dma: use dmaengine_desc_set_callback()

[Joe Damato <joe@dama.to>]

On Tue, Nov 03, 2026 at 09:06:03AM -0600, Frank Li wrote:
> On Mon, Nov 02, 2026 at 03:28:33PM -0800, Joe Damato wrote:
> > On Mon, Nov 02, 2026 at 02:19:16PM -0500, Frank.Li@oss.nxp.com wrote:
> > > From: Frank Li <Frank.Li@nxp.com>
> > >
> > > Replace open-coded assignments to callback and callback_param fields
> > > of struct dma_async_tx_descriptor with calls to the
> > > dmaengine_desc_set_callback() helper across net drivers.
> > >
> > > No functional change intended. Prepare to make struct
> > > dma_async_tx_descriptor private to the DMA engine.
> > >
> > > Signed-off-by: Frank Li <Frank.Li@nxp.com>
> > > ---
> > >  drivers/net/ethernet/allwinner/sun4i-emac.c       |  3 +--
> > >  drivers/net/ethernet/micrel/ks8842.c              |  6 ++----
> > >  drivers/net/ethernet/xilinx/xilinx_axienet_main.c |  6 ++----
> > >  drivers/net/wwan/qcom_bam_dmux.c                  | 10 ++++------
> > >  4 files changed, 9 insertions(+), 16 deletions(-)
> >
> > [...]
> >
> > > diff --git a/drivers/net/wwan/qcom_bam_dmux.c b/drivers/net/wwan/qcom_bam_dmux.c
> > > index cc6ace8d64371..1479f8362e04e 100644
> > > --- a/drivers/net/wwan/qcom_bam_dmux.c
> > > +++ b/drivers/net/wwan/qcom_bam_dmux.c
> > > @@ -195,9 +195,8 @@ static bool bam_dmux_skb_dma_submit_tx(struct bam_dmux_skb_dma *skb_dma)
> > >  		return false;
> > >  	}
> > >
> > > -	desc->callback = bam_dmux_tx_callback;
> > > -	desc->callback_param = skb_dma;
> > > -	desc->cookie = dmaengine_submit(desc);
> > > +	dmaengine_desc_set_callback(desc, bam_dmux_tx_callback, NULL, skb_dma);
> > > +	dmaengine_submit(desc);
> > >  	return true;
> > >  }
> > >
> > > @@ -477,9 +476,8 @@ static bool bam_dmux_skb_dma_submit_rx(struct bam_dmux_skb_dma *skb_dma)
> > >  		return false;
> > >  	}
> > >
> > > -	desc->callback = bam_dmux_rx_callback;
> > > -	desc->callback_param = skb_dma;
> > > -	desc->cookie = dmaengine_submit(desc);
> > > +	dmaengine_desc_set_callback(desc, bam_dmux_rx_callback, NULL, skb_dma);
> > > +	dmaengine_submit(desc);
> >
> > I noticed in the above that the return value of dmaengine_submit is discarded
> > instead of stored.
> >
> > Is that intentional? I suppose it might be because AFAICT cookie is never
> > used and the commit message says "no functional change intended".
> 
> dma_cookie_assign() already set desc->cookie in dmaengine_submit(). Of couse
> it is not obvious. Do you need me update commit message to descript it.

Ah, I see it now. In the tx_submit callback it looks like dma drivers set the
cookie.

So removing it here really is a no-op since it was getting set, as you said,
during submit.

My mistake. I don't think it's worth respinning just to fix the commit
message just because I didn't dig deep enough :)