In some configurations, a single TAI can be responsible for multiple
mvpp2 interfaces. However, the mvpp2 driver will call mvpp22_tai_stop
and mvpp22_tai_start per interface RX timestamp disable/enable.

As a result, disabling timestamping for one interface would stop the
worker and corrupt the other interface's RX timestamps.

This commit solves the issue by introducing a simpler ref count for each
TAI instance.

Due to the ref count, we need now to lock tai->lock before doing
anything, as a result, we can't update the current ts using
mvpp22_tai_gettimex64 as it will cause a deadlock. Therefore, we will
just schedule the worker to start immediately.

Fixes: ce3497e2072e ("net: mvpp2: ptp: add support for receive timestamping")
Signed-off-by: Shmuel Hazan <shmuel.h@siklu.com>
---
 .../net/ethernet/marvell/mvpp2/mvpp2_tai.c    | 30 ++++++++++++++++---
 1 file changed, 26 insertions(+), 4 deletions(-)

diff --git a/drivers/net/ethernet/marvell/mvpp2/mvpp2_tai.c b/drivers/net/ethernet/marvell/mvpp2/mvpp2_tai.c
index 95862aff49f1..2e3d43b1bac1 100644
--- a/drivers/net/ethernet/marvell/mvpp2/mvpp2_tai.c
+++ b/drivers/net/ethernet/marvell/mvpp2/mvpp2_tai.c
@@ -61,6 +61,7 @@ struct mvpp2_tai {
 	u64 period;		// nanosecond period in 32.32 fixed point
 	/* This timestamp is updated every two seconds */
 	struct timespec64 stamp;
+	u16 poll_worker_refcount;
 };
 
 static void mvpp2_tai_modify(void __iomem *reg, u32 mask, u32 set)
@@ -368,18 +369,39 @@ void mvpp22_tai_tstamp(struct mvpp2_tai *tai, u32 tstamp,
 	hwtstamp->hwtstamp = timespec64_to_ktime(ts);
 }
 
+static void mvpp22_tai_start_unlocked(struct mvpp2_tai *tai)
+{
+	tai->poll_worker_refcount++;
+	if (tai->poll_worker_refcount > 1)
+		return;
+
+	ptp_schedule_worker(tai->ptp_clock, 0);
+}
+
 void mvpp22_tai_start(struct mvpp2_tai *tai)
 {
-	long delay;
+	unsigned long flags;
 
-	delay = mvpp22_tai_aux_work(&tai->caps);
+	spin_lock_irqsave(&tai->lock, flags);
+	mvpp22_tai_start_unlocked(tai);
+	spin_unlock_irqrestore(&tai->lock, flags);
+}
 
-	ptp_schedule_worker(tai->ptp_clock, delay);
+static void mvpp22_tai_stop_unlocked(struct mvpp2_tai *tai)
+{
+	tai->poll_worker_refcount--;
+	if (tai->poll_worker_refcount)
+		return;
+	ptp_cancel_worker_sync(tai->ptp_clock);
 }
 
 void mvpp22_tai_stop(struct mvpp2_tai *tai)
 {
-	ptp_cancel_worker_sync(tai->ptp_clock);
+	unsigned long flags;
+
+	spin_lock_irqsave(&tai->lock, flags);
+	mvpp22_tai_stop_unlocked(tai);
+	spin_unlock_irqrestore(&tai->lock, flags);
 }
 
 static void mvpp22_tai_remove(void *priv)
-- 
2.40.0

On Wed, 19 Apr 2023 18:14:55 +0300 Shmuel Hazan wrote:
> +static void mvpp22_tai_stop_unlocked(struct mvpp2_tai *tai)
> +{
> +	tai->poll_worker_refcount--;
> +	if (tai->poll_worker_refcount)
> +		return;
> +	ptp_cancel_worker_sync(tai->ptp_clock);

How can you cancel it _sync() when the work takes the same
lock you're already holding? 

https://elixir.bootlin.com/linux/v6.3-rc7/source/drivers/net/ethernet/marvell/mvpp2/mvpp2_tai.c#L246

>  void mvpp22_tai_stop(struct mvpp2_tai *tai)
>  {
> -	ptp_cancel_worker_sync(tai->ptp_clock);
> +	unsigned long flags;
> +
> +	spin_lock_irqsave(&tai->lock, flags);
> +	mvpp22_tai_stop_unlocked(tai);

-- 
pw-bot: cr

On Thu, 2023-04-20 at 20:20 -0700, Jakub Kicinski wrote:
> > Caution: This is an external email. Please take care when clicking
> > links or opening attachments.
> > 
> > 
> > On Wed, 19 Apr 2023 18:14:55 +0300 Shmuel Hazan wrote:
> > > > +static void mvpp22_tai_stop_unlocked(struct mvpp2_tai *tai)
> > > > +{
> > > > +     tai->poll_worker_refcount--;
> > > > +     if (tai->poll_worker_refcount)
> > > > +             return;
> > > > +     ptp_cancel_worker_sync(tai->ptp_clock);
> > 
> > How can you cancel it _sync() when the work takes the same
> > lock you're already holding?
> > 
> > https://elixir.bootlin.com/linux/v6.3-rc7/source/drivers/net/ethernet/marvell/mvpp2/mvpp2_tai.c#L246


Hi Jakub,

Thanks for finding that. Strange that I have not encountered any
deadlocks while testing; I will apply a fix and resend after testing
it.  

> > 
> > > >  void mvpp22_tai_stop(struct mvpp2_tai *tai)
> > > >  {
> > > > -     ptp_cancel_worker_sync(tai->ptp_clock);
> > > > +     unsigned long flags;
> > > > +
> > > > +     spin_lock_irqsave(&tai->lock, flags);
> > > > +     mvpp22_tai_stop_unlocked(tai);
> > 
> > --
> > pw-bot: cr