netdev - RE: [PATCH 1/3] enetc: add hardware timestamping support

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Date:   Mon, 20 May 2019 03:25:45 +0000
From:   "Y.b. Lu" <yangbo.lu@....com>
To:     Claudiu Manoil <claudiu.manoil@....com>,
        Richard Cochran <richardcochran@...il.com>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Shawn Guo <shawnguo@...nel.org>,
        Rob Herring <robh+dt@...nel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/3] enetc: add hardware timestamping support

Hi,

> -----Original Message-----
> From: Claudiu Manoil
> Sent: Thursday, May 16, 2019 11:31 PM
> To: Richard Cochran <richardcochran@...il.com>; Y.b. Lu
> <yangbo.lu@....com>
> Cc: netdev@...r.kernel.org; David Miller <davem@...emloft.net>; Shawn
> Guo <shawnguo@...nel.org>; Rob Herring <robh+dt@...nel.org>;
> devicetree@...r.kernel.org; linux-arm-kernel@...ts.infradead.org;
> linux-kernel@...r.kernel.org
> Subject: RE: [PATCH 1/3] enetc: add hardware timestamping support
> 
> 
> >-----Original Message-----
> >From: Richard Cochran <richardcochran@...il.com>
> >Sent: Thursday, May 16, 2019 5:33 PM
> >To: Y.b. Lu <yangbo.lu@....com>
> >Cc: netdev@...r.kernel.org; David Miller <davem@...emloft.net>; Claudiu
> >Manoil <claudiu.manoil@....com>; Shawn Guo <shawnguo@...nel.org>;
> Rob
> >Herring <robh+dt@...nel.org>; devicetree@...r.kernel.org; linux-arm-
> >kernel@...ts.infradead.org; linux-kernel@...r.kernel.org
> >Subject: Re: [PATCH 1/3] enetc: add hardware timestamping support
> >
> >On Thu, May 16, 2019 at 09:59:08AM +0000, Y.b. Lu wrote:
> >
> [...]
> >
> >>  static bool enetc_clean_tx_ring(struct enetc_bdr *tx_ring, int
> >> napi_budget)  {
> >>  	struct net_device *ndev = tx_ring->ndev;
> >> +	struct enetc_ndev_priv *priv = netdev_priv(ndev);
> >>  	int tx_frm_cnt = 0, tx_byte_cnt = 0;
> >>  	struct enetc_tx_swbd *tx_swbd;
> >> +	union enetc_tx_bd *txbd;
> >> +	bool do_tstamp;
> >>  	int i, bds_to_clean;
> >> +	u64 tstamp = 0;
> >
> >Please keep in reverse Christmas tree order as much as possible:
> 
> For the xmass tree part, Yangbo, better move the priv and txbd declarations
> inside the scope of the if() {} block where they are actually used, i.e.:
> 
> 		if (unlikely(tx_swbd->check_wb)) {
> 			struct enetc_ndev_priv *priv = netdev_priv(ndev);
> 			union enetc_tx_bd *txbd;
> 			[...]
> 		}
> 

[Y.b. Lu] Will do that.

> >
> >	union enetc_tx_bd *txbd;
> >	int i, bds_to_clean;
> >	bool do_tstamp;
> >	u64 tstamp = 0;
> >
> >>  	i = tx_ring->next_to_clean;
> >>  	tx_swbd = &tx_ring->tx_swbd[i];
> >>  	bds_to_clean = enetc_bd_ready_count(tx_ring, i);
> >>
> >> +	do_tstamp = false;
> >> +
> >>  	while (bds_to_clean && tx_frm_cnt < ENETC_DEFAULT_TX_WORK) {
> >>  		bool is_eof = !!tx_swbd->skb;
> >>
> >> +		if (unlikely(tx_swbd->check_wb)) {
> >> +			txbd = ENETC_TXBD(*tx_ring, i);
> >> +
> >> +			if (!(txbd->flags & ENETC_TXBD_FLAGS_W))
> >> +				goto no_wb;
> >> +
> >> +			if (tx_swbd->do_tstamp) {
> >> +				enetc_get_tx_tstamp(&priv->si->hw, txbd,
> >> +						    &tstamp);
> >> +				do_tstamp = true;
> >> +			}
> >> +		}
> >> +no_wb:
> >
> >This goto seems strange and unnecessary.  How about this instead?
> >
> >			if (txbd->flags & ENETC_TXBD_FLAGS_W &&
> >			    tx_swbd->do_tstamp) {
> >				enetc_get_tx_tstamp(&priv->si->hw, txbd, &tstamp);
> >				do_tstamp = true;
> >			}
> >
> 
> Absolutely, somehow I missed this.  I guess the intention was to be able to
> support multiple
> if() blocks for the writeback case (W flag set) but the code is much better off
> without the goto.

[Y.b. Lu] Will use this to support current single tstamp writeback case.

> 
> >>  		enetc_unmap_tx_buff(tx_ring, tx_swbd);
> >>  		if (is_eof) {
> >> +			if (unlikely(do_tstamp)) {
> >> +				enetc_tstamp_tx(tx_swbd->skb, tstamp);
> >> +				do_tstamp = false;
> >> +			}
> >>  			napi_consume_skb(tx_swbd->skb, napi_budget);
> >>  			tx_swbd->skb = NULL;
> >>  		}
> >> @@ -167,6 +169,11 @@ struct enetc_cls_rule {
> >>
> >>  #define ENETC_MAX_BDR_INT	2 /* fixed to max # of available cpus */
> >>
> >> +enum enetc_hw_features {
> >
> >This is a poor choice of name.  It sounds like it describes HW
> >capabilities, but you use it to track whether a feature is requested at
> >run time.
> >
> >> +	ENETC_F_RX_TSTAMP	= BIT(0),
> >> +	ENETC_F_TX_TSTAMP	= BIT(1),
> >> +};
> >> +
> >>  struct enetc_ndev_priv {
> >>  	struct net_device *ndev;
> >>  	struct device *dev; /* dma-mapping device */ @@ -178,6 +185,7 @@
> >> struct enetc_ndev_priv {
> >>  	u16 rx_bd_count, tx_bd_count;
> >>
> >>  	u16 msg_enable;
> >> +	int hw_features;
> >
> >This is also poorly named.  How about "tstamp_request" instead?
> >
> 
> This ndev_priv variable was intended to gather flags for all the active h/w
> related features, i.e. keeping count of what h/w offloads are enabled for the
> current device (at least for those that don't have already a netdev_features_t
> flag).
> I wouldn't waste an int for 2 timestamp flags, I'd rather have a more generic
> name.
> Maybe active_offloads then?
> 
> Anyway, the name can be changed later too, when other offloads will be
> added.

[Y.b. Lu] How about using active_offloads, and add TODO comments in enum enetc_active_offloads?

> 
> Thanks,
> Claudiu