linux-kernel - Re: [net-next] enetc: add support Credit Based Shaper(CBS) for hardware offload

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Message-ID: <20191123190209.5ad772fc@cakuba.netronome.com>
Date:   Sat, 23 Nov 2019 19:02:09 -0800
From:   Jakub Kicinski <jakub.kicinski@...ronome.com>
To:     Po Liu <po.liu@....com>
Cc:     "davem@...emloft.net" <davem@...emloft.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "vinicius.gomes@...el.com" <vinicius.gomes@...el.com>,
        Claudiu Manoil <claudiu.manoil@....com>,
        Vladimir Oltean <vladimir.oltean@....com>,
        Alexandru Marginean <alexandru.marginean@....com>,
        Xiaoliang Yang <xiaoliang.yang_1@....com>,
        Roy Zang <roy.zang@....com>, Mingkai Hu <mingkai.hu@....com>,
        Jerry Huang <jerry.huang@....com>, Leo Li <leoyang.li@....com>
Subject: Re: [net-next] enetc: add support Credit Based Shaper(CBS) for
 hardware offload

On Fri, 22 Nov 2019 07:17:18 +0000, Po Liu wrote:
> +	if (tc == prio_top) {
> +		max_interference_size = port_frame_max_size * 8;
> +	} else {
> +		u32 m0, ma, r0, ra;
> +
> +		m0 = port_frame_max_size * 8;
> +		ma = enetc_port_rd(&si->hw, ENETC_PTCMSDUR(prio_top)) * 8;
> +		ra = enetc_get_cbs_bw(&si->hw, prio_top) *
> +			port_transmit_rate * 10000ULL;
> +		r0 = port_transmit_rate * 1000000ULL;
> +		max_interference_size = m0 + ma + (u64)ra * m0 / (r0 - ra);
> +	}
> +
> +	/* hiCredit bits calculate by:
> +	 *
> +	 * maxSizedFrame * (idleSlope/portTxRate)
> +	 */
> +	hi_credit_bit = max_interference_size * bw / 100;
> +
> +	/* hiCredit bits to hiCredit register need to calculated as:
> +	 *
> +	 * (enetClockFrequency / portTransmitRate) * 100
> +	 */
> +	hi_credit_reg = (ENETC_CLK * 100ULL) * hi_credit_bit
> +			/ (port_transmit_rate * 1000000ULL);

Hi! The patch looks good to me, but I'm concerned about those 64bit
divisions here. Don't these need to be div_u64() & co.? Otherwise
we may see one of the:

ERROR: "__udivdi3" [drivers/net/ethernet/freescale/enetc/fsl-enetc.ko] undefined!

messages from the build bot..

I could be wrong, I haven't actually tested..