netdev - Re: [PATCH 1/3] can: m_can: add Bosch M

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Date:	Wed, 2 Jul 2014 14:33:49 +0800
From:	Dong Aisheng <b29396@...escale.com>
To:	Marc Kleine-Budde <mkl@...gutronix.de>
CC:	<linux-can@...r.kernel.org>, <netdev@...r.kernel.org>,
	<wg@...ndegger.com>, <devicetree@...r.kernel.org>
Subject: Re: [PATCH 1/3] can: m_can: add Bosch M_CAN controller support

On Wed, Jul 02, 2014 at 09:57:50AM +0200, Marc Kleine-Budde wrote:
> On 07/02/2014 08:20 AM, Dong Aisheng wrote:
> [...]
> 
> >>> +static int m_can_do_rx_poll(struct net_device *dev, int quota)
> >>> +{
> >>> +	struct m_can_priv *priv = netdev_priv(dev);
> >>> +	struct net_device_stats *stats = &dev->stats;
> >>> +	struct sk_buff *skb;
> >>> +	struct can_frame *frame;
> >>> +	u32 rxfs, flags, fgi;
> >>> +	u32 num_rx_pkts = 0;
> >>> +
> >>> +	rxfs = m_can_read(priv, M_CAN_RXF0S);
> >>> +	if (!(rxfs & RXFS_FFL_MASK)) {
> >>> +		netdev_dbg(dev, "no messages in fifo0\n");
> >>> +		return 0;
> >>> +	}
> >>> +
> >>> +	while ((rxfs & RXFS_FFL_MASK) && (quota > 0)) {
> >>> +		netdev_dbg(dev, "fifo0 status 0x%x\n", rxfs);
> >>
> >> Please remove the netdev_dbg(), once the driver is stable it should be
> >> of no use.
> >>
> > 
> > Got it.
> > 
> >>> +		if (rxfs & RXFS_RFL)
> >>> +			netdev_warn(dev, "Rx FIFO 0 Message Lost\n");
> >>
> >> What does that mean? Can you still rx the message if it's lost?
> >>
> > 
> > It just warns that there's a message lost, but there are still other
> > message in fifo to receive.
> > 
> >>> +
> >>> +		skb = alloc_can_skb(dev, &frame);
> >>> +		if (!skb) {
> >>> +			stats->rx_dropped++;
> >>> +			return -ENOMEM;
> >>
> >> Have a look at the user of m_can_do_rx_poll() and how it makes use of
> >> the return value.
> >>
> > 
> > Right, thanks for spotting it.
> > 
> >>> +		}
> >>> +
> >>> +		fgi = (rxfs & RXFS_FGI_MASK) >> RXFS_FGI_OFF;
> >>
> >> BTW: Is this a _real_ fifo? Or evolution of the c_can/d_can interface
> >> where it's not a fifo at all.
> >>
> > 
> > Yes, it is real fifo in the message ram.
> > 
> >>> +		flags = readl(priv->mram_base + priv->rxf0_off + fgi * 16);
> >>> +		if (flags & RX_BUF_XTD)
> >>> +			frame->can_id = (flags & CAN_EFF_MASK) | CAN_EFF_FLAG;
> >>> +		else
> >>> +			frame->can_id = (flags >> 18) & CAN_SFF_MASK;
> >>> +		netdev_dbg(dev, "R0 0x%x\n", flags);
> >>
> >> please remove dbg
> >>> +
> >>> +		if (flags & RX_BUF_RTR) {
> >>> +			frame->can_id |= CAN_RTR_FLAG;
> >>> +		} else {
> >>> +			flags = readl(priv->mram_base +
> >>> +					priv->rxf0_off + fgi * 16 + 0x4);
> >>> +			frame->can_dlc = get_can_dlc((flags >> 16) & 0x0F);
> >>> +			netdev_dbg(dev, "R1 0x%x\n", flags);
> >>
> >> please remove
> >>
> >>> +
> >>> +			*(u32 *)(frame->data + 0) = readl(priv->mram_base +
> >>> +					priv->rxf0_off + fgi * 16 + 0x8);
> >>> +			*(u32 *)(frame->data + 4) = readl(priv->mram_base +
> >>> +					priv->rxf0_off + fgi * 16 + 0xC);
> >>
> >>
> >> can you create a wrapper function to hide the pointer arithmetics here?
> >> Somethig like m_can_read_fifo()
> >>
> > 
> > Yes, i could make a wrapper function for it.
> > 
> >>> +			netdev_dbg(dev, "R2 0x%x\n", *(u32 *)(frame->data + 0));
> >>> +			netdev_dbg(dev, "R3 0x%x\n", *(u32 *)(frame->data + 4));
> >>> +		}
> >>> +
> >>> +		/* acknowledge rx fifo 0 */
> >>> +		m_can_write(priv, M_CAN_RXF0A, fgi);
> >>> +
> >>> +		netif_receive_skb(skb);
> >>> +		netdev_dbg(dev, "new packet received\n");
> >>> +
> >>> +		stats->rx_packets++;
> >>> +		stats->rx_bytes += frame->can_dlc;
> >>
> >> Please move the stats handling in front of netif_receive_skb() as the
> >> skb and thus frame is not a valid pointer anymore.
> >>
> > 
> > Good catch!
> > Will change it.
> > 
> >>> +
> >>> +		can_led_event(dev, CAN_LED_EVENT_RX);
> >>
> >> Please move out of the loop so that it is just called once (if a CAN
> >> frame is rx'ed) per  m_can_do_rx_poll().
> 
> > Why that?
> > The purpose is calling it for each new packet received.
> 
> It will only trigger LED blinking, and tglx pointed out, that we don't
> need the overhead of calling it for every CAN frame.
> 

Okay, got it, thanks for this information.

Regards
Dong Aisheng

> Marc
> 
> -- 
> Pengutronix e.K.                  | Marc Kleine-Budde           |
> Industrial Linux Solutions        | Phone: +49-231-2826-924     |
> Vertretung West/Dortmund          | Fax:   +49-5121-206917-5555 |
> Amtsgericht Hildesheim, HRA 2686  | http://www.pengutronix.de   |
> 


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