netdev - Re: [PATCH 6/7] net: dsa: b53: Add logic for TX timestamping

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Message-ID: <4f4e28f9-8d1e-f2e9-aa0c-37b2c4cd8e8a@gmail.com>
Date:   Fri, 5 Nov 2021 19:50:43 -0700
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Martin Kaistra <martin.kaistra@...utronix.de>,
        Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>
Cc:     Richard Cochran <richardcochran@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>,
        John Stultz <john.stultz@...aro.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Stephen Boyd <sboyd@...nel.org>,
        Russell King <linux@...linux.org.uk>,
        Marc Kleine-Budde <mkl@...gutronix.de>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH 6/7] net: dsa: b53: Add logic for TX timestamping



On 11/4/2021 6:32 AM, Martin Kaistra wrote:
> In order to get the switch to generate a timestamp for a transmitted
> packet, we need to set the TS bit in the BRCM tag. The switch will then
> create a status frame, which gets send back to the cpu.
> In b53_port_txtstamp() we put the skb into a waiting position.
> 
> When a status frame is received, we extract the timestamp and put the time
> according to our timecounter into the waiting skb. When
> TX_TSTAMP_TIMEOUT is reached and we have no means to correctly get back
> a full timestamp, we cancel the process.
> 
> As the status frame doesn't contain a reference to the original packet,
> only one packet with timestamp request can be sent at a time.
> 
> Signed-off-by: Martin Kaistra <martin.kaistra@...utronix.de>
> ---

[snip]

> +static long b53_hwtstamp_work(struct ptp_clock_info *ptp)
> +{
> +	struct b53_device *dev =
> +		container_of(ptp, struct b53_device, ptp_clock_info);
> +	struct dsa_switch *ds = dev->ds;
> +	int i;
> +
> +	for (i = 0; i < ds->num_ports; i++) {
> +		struct b53_port_hwtstamp *ps;
> +
> +		if (!dsa_is_user_port(ds, i))
> +			continue;

Can you also check on !dsa_port_is_unused()?

[snip]

>   #endif
> diff --git a/net/dsa/tag_brcm.c b/net/dsa/tag_brcm.c
> index 85dc47c22008..53cd0345df1b 100644
> --- a/net/dsa/tag_brcm.c
> +++ b/net/dsa/tag_brcm.c
> @@ -8,6 +8,7 @@
>   #include <linux/dsa/brcm.h>
>   #include <linux/etherdevice.h>
>   #include <linux/list.h>
> +#include <linux/ptp_classify.h>
>   #include <linux/slab.h>
>   #include <linux/dsa/b53.h>
>   
> @@ -85,9 +86,14 @@ static struct sk_buff *brcm_tag_xmit_ll(struct sk_buff *skb,
>   					unsigned int offset)
>   {
>   	struct dsa_port *dp = dsa_slave_to_port(dev);
> +	struct b53_device *b53_dev = dp->ds->priv;
> +	unsigned int type = ptp_classify_raw(skb);
>   	u16 queue = skb_get_queue_mapping(skb);
> +	struct b53_port_hwtstamp *ps;
>   	u8 *brcm_tag;
>   
> +	ps = &b53_dev->ports[dp->index].port_hwtstamp;

The dsa_port structure as a priv member which would be well suited to 
store &b53_dev->ports[dp->index].port_hwtstamp and avoid traversing 
multiple layers of objects here. You don't need to need b53_device at 
all, and even if you did, you could easily add a back pointer to it in 
port_hwstamp.

This applies below as well in brcm_tag_rcv_ll

[snip]

> +
>   /* Frames with this tag have one of these two layouts:
>    * -----------------------------------
>    * | MAC DA | MAC SA | 4b tag | Type | DSA_TAG_PROTO_BRCM
> @@ -143,6 +181,9 @@ static struct sk_buff *brcm_tag_rcv_ll(struct sk_buff *skb,
>   				       unsigned int offset,
>   				       int *tag_len)
>   {
> +	struct b53_port_hwtstamp *ps;
> +	struct b53_device *b53_dev;
> +	struct dsa_port *dp;
>   	int source_port;
>   	u8 *brcm_tag;
>   	u32 tstamp;
> @@ -174,6 +215,16 @@ static struct sk_buff *brcm_tag_rcv_ll(struct sk_buff *skb,
>   	if (!skb->dev)
>   		return NULL;
>   
> +	/* Check whether this is a status frame */
> +	if (*tag_len == 8 && brcm_tag[3] & 0x20) {

Can we have an unlikely() here, because this is unlikely to happen 
except for switches that do support PTP, and we only have 53128 so far.

Also a define for this 0x20 would be nice, it is the timestamp bit for 
the packet.
-- 
Florian