linux-kernel - Re: [PATCH net-next v5 1/2] net: ethernet: ti: am65-cpts: Enable RX HW timestamp for PTP packets using CPTS FIFO

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Date: Thu, 04 Apr 2024 12:40:38 +0200
From: Paolo Abeni <pabeni@...hat.com>
To: Chintan Vankar <c-vankar@...com>, Dan Carpenter
 <dan.carpenter@...aro.org>,  Siddharth Vadapalli <s-vadapalli@...com>,
 Heiner Kallweit <hkallweit1@...il.com>, Andrew Lunn <andrew@...n.ch>, Roger
 Quadros <rogerq@...nel.org>, Richard Cochran <richardcochran@...il.com>,
 Jakub Kicinski <kuba@...nel.org>, Eric Dumazet <edumazet@...gle.com>,
 "David S. Miller" <davem@...emloft.net>
Cc: linux-kernel@...r.kernel.org, netdev@...r.kernel.org
Subject: Re: [PATCH net-next v5 1/2] net: ethernet: ti: am65-cpts: Enable RX
 HW timestamp for PTP packets using CPTS FIFO

On Tue, 2024-04-02 at 17:14 +0530, Chintan Vankar wrote:
> Add a new function "am65_cpts_rx_timestamp()" which checks for PTP
> packets from header and timestamps them.
> 
> Add another function "am65_cpts_find_rx_ts()" which finds CPTS FIFO
> Event to get the timestamp of received PTP packet.
> 
> Signed-off-by: Chintan Vankar <c-vankar@...com>
> ---
> 
> Link to v4:
> https://lore.kernel.org/r/20240327054234.1906957-1-c-vankar@ti.com/
> 
> Changes from v4 to v5:
> - Updated commit message.
> - Replaced "list_del_entry()" and "list_add()" functions with equivalent
>   "list_move()" function.
> 
>  drivers/net/ethernet/ti/am65-cpts.c | 64 +++++++++++++++++++++++++++++
>  drivers/net/ethernet/ti/am65-cpts.h |  6 +++
>  2 files changed, 70 insertions(+)
> 
> diff --git a/drivers/net/ethernet/ti/am65-cpts.c b/drivers/net/ethernet/ti/am65-cpts.c
> index c66618d91c28..bc0bfda1db12 100644
> --- a/drivers/net/ethernet/ti/am65-cpts.c
> +++ b/drivers/net/ethernet/ti/am65-cpts.c
> @@ -906,6 +906,70 @@ static int am65_skb_get_mtype_seqid(struct sk_buff *skb, u32 *mtype_seqid)
>  	return 1;
>  }
>  
> +static u64 am65_cpts_find_rx_ts(struct am65_cpts *cpts, u32 skb_mtype_seqid)
> +{
> +	struct list_head *this, *next;
> +	struct am65_cpts_event *event;
> +	unsigned long flags;
> +	u32 mtype_seqid;
> +	u64 ns = 0;
> +
> +	am65_cpts_fifo_read(cpts);
> +	spin_lock_irqsave(&cpts->lock, flags);

am65_cpts_fifo_read() acquires and releases this same lock. If moving
to a lockless schema is too complex, you should at least try to acquire
the lock only once. e.g. factor out a lockless  __am65_cpts_fifo_read
variant and explicitly acquire the lock before invoke it.

> +	list_for_each_safe(this, next, &cpts->events) {
> +		event = list_entry(this, struct am65_cpts_event, list);
> +		if (time_after(jiffies, event->tmo)) {
> +			list_del_init(&event->list);
> +			list_add(&event->list, &cpts->pool);

Jakub suggested to use list_move() in v4, you should apply that here,
too.

Cheers,

Paolo