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Date:   Thu, 1 Dec 2016 20:16:48 +0800
From:   Jisheng Zhang <jszhang@...vell.com>
To:     Marcin Wojtas <mw@...ihalf.com>
CC:     Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        Andrew Lunn <andrew@...n.ch>,
        Jason Cooper <jason@...edaemon.net>,
        Arnd Bergmann <arnd@...db.de>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, Dmitri Epshtein <dima@...vell.com>,
        Nadav Haklai <nadavh@...vell.com>,
        "Yelena Krivosheev" <yelena@...vell.com>,
        Gregory CLEMENT <gregory.clement@...e-electrons.com>,
        "David S. Miller" <davem@...emloft.net>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH v5 net-next 4/7] net: mvneta: Convert to be 64 bits
 compatible

On Thu, 1 Dec 2016 20:02:05 +0800 Jisheng Zhang wrote:

> Hi Marcin,
> 
> On Thu, 1 Dec 2016 12:48:39 +0100 Marcin Wojtas wrote:
> 
> > Hi Jisheng,
> > 
> > Which baseline do you use?
> > 
> > It took me really lot of time to catch why RX broke after rebase from
> > LKv4.1 to LKv4.4. Between those two, in commit:
> > 97303480753e ("arm64: Increase the max granular size")
> > L1_CACHE_BYTES for all ARMv8 platforms was increased to 128B and so
> > did NET_SKB_PAD.
> > 
> > And 128 is more than the maximum that can fit into packet offset
> > [11:8]@0x1400. In such case this correction is needed. Did it answer
> > your doubts?  
> 
> That's key! Thanks a lot. In my repo, we don't have commit 97303480753e
> ("arm64: Increase the max granular size")
> 
> I think it would be great if this information can be added into the commit
> msg.
> 
> IIRC, arm64 maintainers considered to let L1_CACHE_BYTES the _minimum_ of
> cache line sizes of arm64. If that's implemented and merged, then we can

I just searched and found the email.

"We may have to revisit this logic and consider L1_CACHE_BYTES the
_minimum_ of cache line sizes in arm64 systems supported by the kernel.
Do you have any benchmarks on Cavium boards that would show significant
degradation with 64-byte L1_CACHE_BYTES vs 128?"

https://patchwork.kernel.org/patch/8634481/


> revert this patch later.
> 
> Thanks,
> Jisheng
> 
> > 
> > Best regards,
> > Marcin
> > 
> > 
> > 
> > 2016-12-01 12:26 GMT+01:00 Jisheng Zhang <jszhang@...vell.com>:  
> > > Hi Gregory, Marcin,
> > >
> > > On Wed, 30 Nov 2016 22:42:49 +0100 Gregory CLEMENT wrote:
> > >    
> > >> From: Marcin Wojtas <mw@...ihalf.com>
> > >>
> > >> Prepare the mvneta driver in order to be usable on the 64 bits platform
> > >> such as the Armada 3700.
> > >>
> > >> [gregory.clement@...e-electrons.com]: this patch was extract from a larger
> > >> one to ease review and maintenance.
> > >>
> > >> Signed-off-by: Marcin Wojtas <mw@...ihalf.com>
> > >> Signed-off-by: Gregory CLEMENT <gregory.clement@...e-electrons.com>
> > >> ---
> > >>  drivers/net/ethernet/marvell/mvneta.c | 17 ++++++++++++++++-
> > >>  1 file changed, 16 insertions(+), 1 deletion(-)
> > >>
> > >> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
> > >> index 92b9af14c352..8ef03fb69bcd 100644
> > >> --- a/drivers/net/ethernet/marvell/mvneta.c
> > >> +++ b/drivers/net/ethernet/marvell/mvneta.c
> > >> @@ -296,6 +296,12 @@
> > >>  /* descriptor aligned size */
> > >>  #define MVNETA_DESC_ALIGNED_SIZE     32
> > >>
> > >> +/* Number of bytes to be taken into account by HW when putting incoming data
> > >> + * to the buffers. It is needed in case NET_SKB_PAD exceeds maximum packet
> > >> + * offset supported in MVNETA_RXQ_CONFIG_REG(q) registers.    
> > >
> > > We also brought up this driver on 64bit platforms, we doesn't have this
> > > patch. Maybe I'm wrong, I'm trying to understand why we need this
> > > modification. Let's assume the NET_SKB_PAD is 64B, we call
> > > mvneta_rxq_offset_set(pp, rxq, 64),
> > >
> > > {
> > >         u32 val;
> > >
> > >         val = mvreg_read(pp, MVNETA_RXQ_CONFIG_REG(rxq->id));
> > >         val &= ~MVNETA_RXQ_PKT_OFFSET_ALL_MASK;
> > >
> > >         /* Offset is in */
> > >         val |= MVNETA_RXQ_PKT_OFFSET_MASK(offset >> 3);
> > > // then this will be "val |= 8;" it doesn't exceeds the max offset of
> > > MVNETA_RXQ_CONFIG_REG(q) register.
> > >
> > > Could you please kindly point out where I am wrong?
> > >    
> > >> + */
> > >> +#define MVNETA_RX_PKT_OFFSET_CORRECTION              64
> > >> +
> > >>  #define MVNETA_RX_PKT_SIZE(mtu) \
> > >>       ALIGN((mtu) + MVNETA_MH_SIZE + MVNETA_VLAN_TAG_LEN + \
> > >>             ETH_HLEN + ETH_FCS_LEN,                        \
> > >> @@ -416,6 +422,7 @@ struct mvneta_port {
> > >>       u64 ethtool_stats[ARRAY_SIZE(mvneta_statistics)];
> > >>
> > >>       u32 indir[MVNETA_RSS_LU_TABLE_SIZE];
> > >> +     u16 rx_offset_correction;
> > >>  };
> > >>
> > >>  /* The mvneta_tx_desc and mvneta_rx_desc structures describe the
> > >> @@ -1807,6 +1814,7 @@ static int mvneta_rx_refill(struct mvneta_port *pp,
> > >>               return -ENOMEM;
> > >>       }
> > >>
> > >> +     phys_addr += pp->rx_offset_correction;
> > >>       mvneta_rx_desc_fill(rx_desc, phys_addr, data, rxq);
> > >>       return 0;
> > >>  }
> > >> @@ -2782,7 +2790,7 @@ static int mvneta_rxq_init(struct mvneta_port *pp,
> > >>       mvreg_write(pp, MVNETA_RXQ_SIZE_REG(rxq->id), rxq->size);
> > >>
> > >>       /* Set Offset */
> > >> -     mvneta_rxq_offset_set(pp, rxq, NET_SKB_PAD);
> > >> +     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);
> > >> @@ -4033,6 +4041,13 @@ static int mvneta_probe(struct platform_device *pdev)
> > >>
> > >>       pp->rxq_def = rxq_def;
> > >>
> > >> +     /* 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.    
> > >
> > > Even we need this patch, I'm not sure this last comment is correct or not.
> > > NET_SKB_PAD is defined as:
> > >
> > > #define NET_SKB_PAD     max(32, L1_CACHE_BYTES)
> > >
> > > we have 64B cacheline 32bit platforms, on this platforms, the NET_SKB_PAD
> > > should be 64B as well.
> > >
> > > Thanks,
> > > Jisheng    
> 
> 
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