linux-kernel - Re: [PATCH v5 net-next 4/7] net: mvneta: Convert to be 64 bits compatible

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Message-ID: <20161201192604.07ed9516@xhacker>
Date:   Thu, 1 Dec 2016 19:26:04 +0800
From:   Jisheng Zhang <jszhang@...vell.com>
To:     Gregory CLEMENT <gregory.clement@...e-electrons.com>,
        Marcin Wojtas <mw@...ihalf.com>
CC:     "David S. Miller" <davem@...emloft.net>,
        <linux-kernel@...r.kernel.org>, <netdev@...r.kernel.org>,
        Arnd Bergmann <arnd@...db.de>,
        Jason Cooper <jason@...edaemon.net>,
        Andrew Lunn <andrew@...n.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        <linux-arm-kernel@...ts.infradead.org>,
        Nadav Haklai <nadavh@...vell.com>,
        Dmitri Epshtein <dima@...vell.com>,
        Yelena Krivosheev <yelena@...vell.com>
Subject: Re: [PATCH v5 net-next 4/7] net: mvneta: Convert to be 64 bits
 compatible

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