netdev - RE: RE: [RESEND] [PATCH 1/1] can: m_can: Control tx and rx flow to avoid communication stall

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Date: Fri, 14 Jul 2023 07:26:01 +0000
From: Kumari Pallavi <kumari.pallavi@...el.com>
To: Marc Kleine-Budde <mkl@...gutronix.de>
CC: "rcsekar@...sung.com" <rcsekar@...sung.com>, "Sangannavar,
 Mallikarjunappa" <mallikarjunappa.sangannavar@...el.com>, "Nikula, Jarkko"
	<jarkko.nikula@...el.com>, "linux-can@...r.kernel.org"
	<linux-can@...r.kernel.org>, "netdev@...r.kernel.org"
	<netdev@...r.kernel.org>, "linux-kernel@...r.kernel.org"
	<linux-kernel@...r.kernel.org>, "Thokala, Srikanth"
	<srikanth.thokala@...el.com>
Subject: RE: RE: [RESEND] [PATCH 1/1] can: m_can: Control tx and rx flow to
 avoid communication stall

Hi Marc,

> -----Original Message-----
> From: Marc Kleine-Budde <mkl@...gutronix.de>
> Sent: Friday, July 7, 2023 1:04 PM
> To: Kumari Pallavi <kumari.pallavi@...el.com>
> Cc: rcsekar@...sung.com; Sangannavar, Mallikarjunappa
> <mallikarjunappa.sangannavar@...el.com>; Nikula, Jarkko
> <jarkko.nikula@...el.com>; linux-can@...r.kernel.org;
> netdev@...r.kernel.org; linux-kernel@...r.kernel.org; Thokala, Srikanth
> <srikanth.thokala@...el.com>
> Subject: Re: RE: [RESEND] [PATCH 1/1] can: m_can: Control tx and rx flow to
> avoid communication stall
> 
> On 07.07.2023 05:38:09, Kumari Pallavi wrote:
> > > >  			if (netif_queue_stopped(dev) &&
> > > >  			    !m_can_tx_fifo_full(cdev))
> > > >  				netif_wake_queue(dev);
> > > > @@ -1787,6 +1787,7 @@ static netdev_tx_t m_can_start_xmit(struct
> > > > sk_buff
> > > *skb,
> > > >  		}
> > > >  	} else {
> > > >  		cdev->tx_skb = skb;
> > > > +		m_can_write(cdev, M_CAN_IE, IR_ALL_INT & (IR_TEFN));
> > >
> > > - What's the purpose of  "()" around IR_TEFN?
> > > - "IR_ALL_INT & (IR_TEFN)" is equal to IR_TEFN, isn't it?
> > > - This basically disables all other interrupts, is this what you want to
> > >   do?
> > > - What happens if the bus is busy with high prio CAN frames and you want
> > >   to send low prio ones? You will not get any RX-IRQ, this doesn't look
> > >   correct to me.
> > >
> >
> > Even though the RX interrupt is disabled (in IE), if there is an TX
> > interrupt and the RF0N bit is set (in IR), the RX packet will still be
> > serviced because the TX and RX share the same IRQ handler.
> 
> If the bus is busy with high prio CAN frames and the m_can wants to send a low
> prio frame, the m_can will not be able to send it's CAN frame, there will be not
> TX interrupt. If there are enough high prio CAN frames the RX buffer will
> overflow.
> 

Sorry for late reply, I agree let me see if I can try to simulate this scenario using CAN
analyzer. I already stressed the current solution for more than 10 days and didn't
observe any issue. However, I will try to incorporate this scenario for stress as well and 
come back.

Thanks,
Pallavi

> regards,
> Marc
> 
> --
> Pengutronix e.K.                 | Marc Kleine-Budde          |
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