linux-kernel - Re: [PATCH 1/5] net: mvneta: fix rx_offset

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Date:   Wed, 29 Aug 2018 17:16:08 +0800
From:   Jisheng Zhang <Jisheng.Zhang@...aptics.com>
To:     Gregory CLEMENT <gregory.clement@...tlin.com>
Cc:     <thomas.petazzoni@...tlin.com>,
        "David S. Miller" <davem@...emloft.net>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Andrew Lunn <andrew@...n.ch>,
        <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/5] net: mvneta: fix rx_offset_correction set and usage

Hi,

On Wed, 29 Aug 2018 11:05:45 +0200 Gregory CLEMENT wrote:

> Hi Jisheng,
>  
>  On mer., août 29 2018, Jisheng Zhang <Jisheng.Zhang@...aptics.com> wrote:
> 
> > The rx_offset_correction is RX packet offset correction for platforms,
> > it's not related with SW BM, instead, it's only related with the
> > platform's NET_SKB_PAD.
> >  
> 
> But if I undrestood well, the value of rx_offset_correction has an
> influence only when we use HW BM.

The rx_offset_correction is introduced by commit 8d5047cf9ca2 ("net: mvneta:
 Convert to be 64 bits compatible"). It's to support mvneta on 64bit
platforms such as Armada 3700. It's not related with HW BM.

> 
> However since d93277b9839b ("Revert "arm64: Increase the max granular
> size""), NET_SKB_PAD is 64 for arm64, so in the end rx_offset_correction
> is always 0 for recent kernels.

yes, I mentioned this in email "[query] about recent mvneta patches".
IMHO, we'd better not rely on the platform's L1_CACHE_BYTES value,
we dunno whether the max granular size is increased again in the future.

Thanks

> 
> Gregory
> 
> 
> > Fix the issue by reverting to the original behavior.
> >
> > Fixes: 562e2f467e71 ("net: mvneta: Improve the buffer allocation method for SWBM")
> > Signed-off-by: Jisheng Zhang <Jisheng.Zhang@...aptics.com>
> > ---
> >  drivers/net/ethernet/marvell/mvneta.c | 24 ++++++++++--------------
> >  1 file changed, 10 insertions(+), 14 deletions(-)
> >
> > diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> > index bc80a678abc3..0ce94f6587a5 100644
> > --- a/drivers/net/ethernet/marvell/mvneta.c
> > +++ b/drivers/net/ethernet/marvell/mvneta.c
> > @@ -2899,21 +2899,18 @@ static void mvneta_rxq_hw_init(struct mvneta_port *pp,
> >  	mvreg_write(pp, MVNETA_RXQ_BASE_ADDR_REG(rxq->id), rxq->descs_phys);
> >  	mvreg_write(pp, MVNETA_RXQ_SIZE_REG(rxq->id), rxq->size);
> >  
> > +	/* Set Offset */
> > +	mvneta_rxq_offset_set(pp, rxq, NET_SKB_PAD - pp->rx_offset_correction);
> > +
> >  	/* Set coalescing pkts and time */
> >  	mvneta_rx_pkts_coal_set(pp, rxq, rxq->pkts_coal);
> >  	mvneta_rx_time_coal_set(pp, rxq, rxq->time_coal);
> >  
> >  	if (!pp->bm_priv) {
> > -		/* Set Offset */
> > -		mvneta_rxq_offset_set(pp, rxq, 0);
> >  		mvneta_rxq_buf_size_set(pp, rxq, pp->frag_size);
> >  		mvneta_rxq_bm_disable(pp, rxq);
> >  		mvneta_rxq_fill(pp, rxq, rxq->size);
> >  	} else {
> > -		/* Set Offset */
> > -		mvneta_rxq_offset_set(pp, rxq,
> > -				      NET_SKB_PAD - pp->rx_offset_correction);
> > -
> >  		mvneta_rxq_bm_enable(pp, rxq);
> >  		/* Fill RXQ with buffers from RX pool */
> >  		mvneta_rxq_long_pool_set(pp, rxq);
> > @@ -4547,7 +4544,13 @@ static int mvneta_probe(struct platform_device *pdev)
> >  	SET_NETDEV_DEV(dev, &pdev->dev);
> >  
> >  	pp->id = global_port_id++;
> > -	pp->rx_offset_correction = 0; /* not relevant for SW BM */
> > +
> > +	/* Set RX packet offset correction for platforms, whose
> > +	 * NET_SKB_PAD, exceeds 64B. It should be 64B for 64-bit
> > +	 * platforms and 0B for 32-bit ones.
> > +	 */
> > +	pp->rx_offset_correction =
> > +		max(0, NET_SKB_PAD - MVNETA_RX_PKT_OFFSET_CORRECTION);
> >  
> >  	/* Obtain access to BM resources if enabled and already initialized */
> >  	bm_node = of_parse_phandle(dn, "buffer-manager", 0);
> > @@ -4562,13 +4565,6 @@ static int mvneta_probe(struct platform_device *pdev)
> >  				pp->bm_priv = NULL;
> >  			}
> >  		}
> > -		/* Set RX packet offset correction for platforms, whose
> > -		 * NET_SKB_PAD, exceeds 64B. It should be 64B for 64-bit
> > -		 * platforms and 0B for 32-bit ones.
> > -		 */
> > -		pp->rx_offset_correction = max(0,
> > -					       NET_SKB_PAD -
> > -					       MVNETA_RX_PKT_OFFSET_CORRECTION);
> >  	}
> >  	of_node_put(bm_node);
> >  
> > -- 
> > 2.18.0
> >  
>