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Date: Fri, 1 Mar 2024 16:36:50 +0530
From: Chintan Vankar <c-vankar@...com>
To: Roger Quadros <rogerq@...nel.org>,
Dan Carpenter
<dan.carpenter@...aro.org>,
Siddharth Vadapalli <s-vadapalli@...com>,
Richard
Cochran <richardcochran@...il.com>,
Paolo Abeni <pabeni@...hat.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 1/2] net: ethernet: ti: am65-cpts: Enable PTP RX
HW timestamp using CPTS FIFO
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@...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)
>>>> {
>>>> }
>>>>
>
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