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Message-ID: <750369ae-71ef-4c07-8c61-14c0cd06ef4b@ti.com>
Date: Fri, 1 Mar 2024 16:36:50 +0530
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Subject: Re: [PATCH net-next 1/2] net: ethernet: ti: am65-cpts: Enable PTP RX
 HW timestamp using CPTS FIFO
Content-Language: en-US
To: Roger Quadros <rogerq@kernel.org>,
        Dan Carpenter
	<dan.carpenter@linaro.org>,
        Siddharth Vadapalli <s-vadapalli@ti.com>,
        Richard
 Cochran <richardcochran@gmail.com>,
        Paolo Abeni <pabeni@redhat.com>, Jakub
 Kicinski <kuba@kernel.org>,
        Eric Dumazet <edumazet@google.com>,
        "David S.
 Miller" <davem@davemloft.net>
CC: <linux-kernel@vger.kernel.org>, <netdev@vger.kernel.org>
References: <20240215110953.3225099-1-c-vankar@ti.com>
 <52ff5e18-3616-478a-ab40-8f9a6f7f3e37@kernel.org>
 <3713e01e-1e48-489b-8ec2-e98471ca22f0@ti.com>
 <0f62faa4-608f-4e8e-98e5-7e6e50e20308@kernel.org>
From: Chintan Vankar <c-vankar@ti.com>
In-Reply-To: <0f62faa4-608f-4e8e-98e5-7e6e50e20308@kernel.org>
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On 26/02/24 18:19, Roger Quadros wrote:
> 
> 
> On 26/02/2024 11:08, Chintan Vankar wrote:
>>
>> On 19/02/24 16:54, Roger Quadros wrote:
>>>
>>> On 15/02/2024 13:09, Chintan Vankar wrote:
>>>> CPTS module supports capturing timestamp for every packet it receives,
>>>> add a new function named "am65_cpts_rx_find_ts()" to get the timestamp
>>>> of received packets from CPTS FIFO.
>>>>
>>>> Add another function named "am65_cpts_rx_timestamp()" which internally
>>>> calls "am65_cpts_rx_find_ts()" function and timestamps the received
>>>> PTP packets.
>>>>
>>>> Signed-off-by: Chintan Vankar <c-vankar@ti.com>
>>>> ---
>>>>    drivers/net/ethernet/ti/am65-cpts.c | 84 +++++++++++++++++++++--------
>>>>    drivers/net/ethernet/ti/am65-cpts.h | 11 ++--
>>>>    2 files changed, 67 insertions(+), 28 deletions(-)
>>>>
>>>> diff --git a/drivers/net/ethernet/ti/am65-cpts.c b/drivers/net/ethernet/ti/am65-cpts.c
>>>> index c66618d91c28..92a3b40e60d6 100644
>>>> --- a/drivers/net/ethernet/ti/am65-cpts.c
>>>> +++ b/drivers/net/ethernet/ti/am65-cpts.c
>>>> @@ -859,29 +859,6 @@ static long am65_cpts_ts_work(struct ptp_clock_info *ptp)
>>>>        return delay;
>>>>    }
>>>>    -/**
>>>> - * am65_cpts_rx_enable - enable rx timestamping
>>>> - * @cpts: cpts handle
>>>> - * @en: enable
>>>> - *
>>>> - * This functions enables rx packets timestamping. The CPTS can timestamp all
>>>> - * rx packets.
>>>> - */
>>>> -void am65_cpts_rx_enable(struct am65_cpts *cpts, bool en)
>>>> -{
>>>> -    u32 val;
>>>> -
>>>> -    mutex_lock(&cpts->ptp_clk_lock);
>>>> -    val = am65_cpts_read32(cpts, control);
>>>> -    if (en)
>>>> -        val |= AM65_CPTS_CONTROL_TSTAMP_EN;
>>>> -    else
>>>> -        val &= ~AM65_CPTS_CONTROL_TSTAMP_EN;
>>>> -    am65_cpts_write32(cpts, val, control);
>>>> -    mutex_unlock(&cpts->ptp_clk_lock);
>>>> -}
>>>> -EXPORT_SYMBOL_GPL(am65_cpts_rx_enable);
>>>> -
>>>>    static int am65_skb_get_mtype_seqid(struct sk_buff *skb, u32 *mtype_seqid)
>>>>    {
>>>>        unsigned int ptp_class = ptp_classify_raw(skb);
>>>> @@ -906,6 +883,67 @@ 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, struct sk_buff *skb,
>>>> +                int ev_type, 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);
>>> am65_cpts_fifo_read() is called from the CPTS interrupt handler and the
>>> event is popped out of the FIFO and pushed into an event list.
>>>
>>> Doesn't this race with that interrupt handler?
>> Could you clarify why there be a race condition ?
> 
> I'm not sure so was asking. The question is, do you have to call
> am65_cpts_fifo_read() here? If yes, could you please add a comment why.

Yes. We need to call "am65_cpts_fifo_read()" here. If we don't call it
here then there will be a race condition for the event to be added to
the list before "am65_cpts_get_rx_ts()" function is called.

If we have to implement it without invoking "am65_cpts_fifo_read()",
then there has to be a check to ensure that the interrupt associated
with the RX Event has successfully added that event to the list.
Otherwise, due to the nature of "spin_lock_irqsave", when the interrupt
has acquired the lock on one CPU, the "am65_cpts_get_rx_ts()" function
running on another CPU might acquire the lock from the interrupt and
search for the RX Event which the "am65_cpts_fifo_read()" invoked by
the interrupt was supposed to add in the event list. This is racy due
to which it is possible that the event is not yet added when
"am65_cpts_get_rx_ts()" is invoked. Therefore, to ensure that the
event is surely present, invoking "am65_cpts_fifo_read()" is
required.

> 
>>> Can't you use that event list instead of reading cpts_fifo directly?
>>>
>>> Something like am65_cpts_match_tx_ts()?
>>>
>>>> +    spin_lock_irqsave(&cpts->lock, flags);
>>>> +    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);
>>>> +            continue;
>>>> +        }
>>>> +
>>>> +        mtype_seqid = event->event1 &
>>>> +                  (AM65_CPTS_EVENT_1_MESSAGE_TYPE_MASK |
>>>> +                   AM65_CPTS_EVENT_1_SEQUENCE_ID_MASK |
>>>> +                   AM65_CPTS_EVENT_1_EVENT_TYPE_MASK);
>>>> +
>>>> +        if (mtype_seqid == skb_mtype_seqid) {
>>>> +            ns = event->timestamp;
>>>> +            list_del_init(&event->list);
>>>> +            list_add(&event->list, &cpts->pool);
>>>> +            break;
>>>> +        }
>>>> +    }
>>>> +    spin_unlock_irqrestore(&cpts->lock, flags);
>>>> +
>>>> +    return ns;
>>>> +}
>>>> +
>>>> +void am65_cpts_rx_timestamp(struct am65_cpts *cpts, struct sk_buff *skb)
>>>> +{
>>>> +    struct am65_cpts_skb_cb_data *skb_cb = (struct am65_cpts_skb_cb_data *)skb->cb;
>>>> +    struct skb_shared_hwtstamps *ssh;
>>>> +    int ret;
>>>> +    u64 ns;
>>>> +
>>>> +    ret = am65_skb_get_mtype_seqid(skb, &skb_cb->skb_mtype_seqid);
>>>> +    if (!ret)
>>>> +        return; /* if not PTP class packet */
>>>> +
>>>> +    skb_cb->skb_mtype_seqid |= (AM65_CPTS_EV_RX << AM65_CPTS_EVENT_1_EVENT_TYPE_SHIFT);
>>>> +
>>>> +    dev_dbg(cpts->dev, "%s mtype seqid %08x\n", __func__, skb_cb->skb_mtype_seqid);
>>>> +
>>>> +    ns = am65_cpts_find_rx_ts(cpts, skb, AM65_CPTS_EV_RX, skb_cb->skb_mtype_seqid);
>>>> +    if (!ns)
>>>> +        return;
>>>> +
>>>> +    ssh = skb_hwtstamps(skb);
>>>> +    memset(ssh, 0, sizeof(*ssh));
>>>> +    ssh->hwtstamp = ns_to_ktime(ns);
>>>> +}
>>>> +EXPORT_SYMBOL_GPL(am65_cpts_rx_timestamp);
>>>> +
>>>>    /**
>>>>     * am65_cpts_tx_timestamp - save tx packet for timestamping
>>>>     * @cpts: cpts handle
>>>> diff --git a/drivers/net/ethernet/ti/am65-cpts.h b/drivers/net/ethernet/ti/am65-cpts.h
>>>> index 6e14df0be113..6099d772799d 100644
>>>> --- a/drivers/net/ethernet/ti/am65-cpts.h
>>>> +++ b/drivers/net/ethernet/ti/am65-cpts.h
>>>> @@ -22,9 +22,9 @@ void am65_cpts_release(struct am65_cpts *cpts);
>>>>    struct am65_cpts *am65_cpts_create(struct device *dev, void __iomem *regs,
>>>>                       struct device_node *node);
>>>>    int am65_cpts_phc_index(struct am65_cpts *cpts);
>>>> +void am65_cpts_rx_timestamp(struct am65_cpts *cpts, struct sk_buff *skb);
>>>>    void am65_cpts_tx_timestamp(struct am65_cpts *cpts, struct sk_buff *skb);
>>>>    void am65_cpts_prep_tx_timestamp(struct am65_cpts *cpts, struct sk_buff *skb);
>>>> -void am65_cpts_rx_enable(struct am65_cpts *cpts, bool en);
>>>>    u64 am65_cpts_ns_gettime(struct am65_cpts *cpts);
>>>>    int am65_cpts_estf_enable(struct am65_cpts *cpts, int idx,
>>>>                  struct am65_cpts_estf_cfg *cfg);
>>>> @@ -48,17 +48,18 @@ static inline int am65_cpts_phc_index(struct am65_cpts *cpts)
>>>>        return -1;
>>>>    }
>>>>    -static inline void am65_cpts_tx_timestamp(struct am65_cpts *cpts,
>>>> +static inline void am65_cpts_rx_timestamp(struct am65_cpts *cpts,
>>>>                          struct sk_buff *skb)
>>>>    {
>>>>    }
>>>>    -static inline void am65_cpts_prep_tx_timestamp(struct am65_cpts *cpts,
>>>> -                           struct sk_buff *skb)
>>>> +static inline void am65_cpts_tx_timestamp(struct am65_cpts *cpts,
>>>> +                      struct sk_buff *skb)
>>>>    {
>>>>    }
>>>>    -static inline void am65_cpts_rx_enable(struct am65_cpts *cpts, bool en)
>>>> +static inline void am65_cpts_prep_tx_timestamp(struct am65_cpts *cpts,
>>>> +                           struct sk_buff *skb)
>>>>    {
>>>>    }
>>>>    
>