linux-kernel - RE: [PATCH] staging: fsl-dpaa2/eth: Add support for hardware timestamping

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Message-ID: <DB6PR0401MB25361EE5633F24AA34F0063CF88E0@DB6PR0401MB2536.eurprd04.prod.outlook.com>
Date:   Thu, 26 Apr 2018 10:17:38 +0000
From:   "Y.b. Lu" <yangbo.lu@....com>
To:     Dan Carpenter <dan.carpenter@...cle.com>
CC:     "devel@...verdev.osuosl.org" <devel@...verdev.osuosl.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Richard Cochran <richardcochran@...il.com>,
        Ruxandra Ioana Ciocoi Radulescu <ruxandra.radulescu@....com>
Subject: RE: [PATCH] staging: fsl-dpaa2/eth: Add support for hardware
 timestamping

Hi Dan,

> -----Original Message-----
> From: Dan Carpenter [mailto:dan.carpenter@...cle.com]
> Sent: Wednesday, April 25, 2018 6:04 PM
> To: Y.b. Lu <yangbo.lu@....com>
> Cc: devel@...verdev.osuosl.org; linux-kernel@...r.kernel.org; Greg
> Kroah-Hartman <gregkh@...uxfoundation.org>; Richard Cochran
> <richardcochran@...il.com>; Ruxandra Ioana Ciocoi Radulescu
> <ruxandra.radulescu@....com>
> Subject: Re: [PATCH] staging: fsl-dpaa2/eth: Add support for hardware
> timestamping
> 
> On Wed, Apr 25, 2018 at 05:17:49PM +0800, Yangbo Lu wrote:
> > @@ -275,6 +278,16 @@ static void dpaa2_eth_rx(struct dpaa2_eth_priv
> > *priv,
> >
> >  	prefetch(skb->data);
> >
> > +	/* Get the timestamp value */
> > +	if (priv->ts_rx_en) {
> > +		struct skb_shared_hwtstamps *shhwtstamps = skb_hwtstamps(skb);
> > +		u64 *ns = dpaa2_get_ts(vaddr, false);
> > +
> > +		*ns = DPAA2_PTP_NOMINAL_FREQ_PERIOD_NS * le64_to_cpup(ns);
> 
> This will cause Sparse endianess warnings.
> 
> I don't totally understand why we're writing to *ns.  Do we access *ns again
> or not?  Either way, this doesn't seem right.  In other words, why don't we
> do this:
> 
> 		__le64 *period = dpaa2_get_ts(vaddr, false);
> 		u64 ns;
> 
> 		ns = DPAA2_PTP_NOMINAL_FREQ_PERIOD_NS *
> le64_to_cpup(period);
> 		memset(shhwtstamps, 0, sizeof(*shhwtstamps));
> 		shhwtstamps->hwtstamp = ns_to_ktime(ns);
> 
> Then if we need to save a munged *ns then we can do this at the end:
> 
> 		/* we need this because blah blah blah */
> 		*period = (__le64)ns;
> 

[Y.b. Lu] You're right. I will modify the code according to your suggestion.

> 
> > +		memset(shhwtstamps, 0, sizeof(*shhwtstamps));
> > +		shhwtstamps->hwtstamp = ns_to_ktime(*ns);
> > +	}
> > +
> >  	/* Check if we need to validate the L4 csum */
> >  	if (likely(dpaa2_fd_get_frc(fd) & DPAA2_FD_FRC_FASV)) {
> >  		status = le32_to_cpu(fas->status);
> 
> [ snip ]
> 
> > @@ -520,6 +561,19 @@ static void free_tx_fd(const struct dpaa2_eth_priv
> *priv,
> >  		return;
> >  	}
> >
> > +	/* Get the timestamp value */
> > +	if (priv->ts_tx_en && skb_shinfo(skb)->tx_flags & SKBTX_HW_TSTAMP) {
> > +		struct skb_shared_hwtstamps shhwtstamps;
> > +		u64 *ns;
> > +
> > +		memset(&shhwtstamps, 0, sizeof(shhwtstamps));
> > +
> > +		ns = dpaa2_get_ts(skbh, true);
> > +		*ns = DPAA2_PTP_NOMINAL_FREQ_PERIOD_NS * le64_to_cpup(ns);
> > +		shhwtstamps.hwtstamp = ns_to_ktime(*ns);
> > +		skb_tstamp_tx(skb, &shhwtstamps);
> 
> Sparse issues here also.

[Y.b. Lu] Will modify the code according to your suggestion.

> 
> > +	}
> > +
> >  	/* Free SGT buffer allocated on tx */
> >  	if (fd_format != dpaa2_fd_single)
> >  		skb_free_frag(skbh);
> > @@ -552,6 +606,10 @@ static netdev_tx_t dpaa2_eth_tx(struct sk_buff
> *skb, struct net_device *net_dev)
> >  			goto err_alloc_headroom;
> >  		}
> >  		percpu_extras->tx_reallocs++;
> > +
> > +		if (skb->sk)
> > +			skb_set_owner_w(ns, skb->sk);
> 
> Is this really related?  (I have not looked at this code).

[Y.b. Lu] Yes. The skb_tstamp_tx() function will check that.

> 
> > +
> >  		dev_kfree_skb(skb);
> >  		skb = ns;
> >  	}
> 
> [ snip ]
> 
> > @@ -319,6 +351,9 @@ struct dpaa2_eth_priv {
> >  	u16 bpid;
> >  	struct iommu_domain *iommu_domain;
> >
> > +	bool ts_tx_en; /* Tx timestamping enabled */
> > +	bool ts_rx_en; /* Rx timestamping enabled */
> 
> These variable names are not great.  I wouldn't have understood "ts_"
> without the comment.  "tx_" is good.  "en" is confusing until you read the
> comment.  But really it should just be left out because "enable" is assumed,
> generally.  Last week I asked someone to rewrite a patch that had a _disable
> variable because negative variables lead to double negatives which screw with
> my tiny head.
> 
> 	if (blah_disable != 0) {
> 
> OH MY BLASTED WORD MY BRIAN ESPLODED!!!1!
> 
> So let's just name these "tx_timestamps" or something.

[Y.b. Lu] Ok. Let me use tx_tstamp/rx_tstamp instead. The tstamp is common used in driver.

> 
> 
> > +
> >  	u16 tx_qdid;
> >  	u16 rx_buf_align;
> >  	struct fsl_mc_io *mc_io;
> 
> regards,
> dan carpenter