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, 7 Jul 2023 09:34:14 +0200
From: Marc Kleine-Budde <mkl@...gutronix.de>
To: Kumari Pallavi <kumari.pallavi@...el.com>
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

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.

regards,
Marc

-- 
Pengutronix e.K.                 | Marc Kleine-Budde          |
Embedded Linux                   | https://www.pengutronix.de |
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