Re: [PATCH v2 09/13] can: pruss CAN driver.

[Subhasish Ghosh]

--------------------------------------------------
From: "Kurt Van Dijck" <kurt.van.dijck@xxxxxx>
Sent: Friday, February 11, 2011 8:50 PM
To: "Subhasish Ghosh" <subhasish@xxxxxxxxxxxxxxxxxxxx>
Cc: <davinci-linux-open-source@xxxxxxxxxxxxxxxxxxxx>; 
<linux-arm-kernel@xxxxxxxxxxxxxxxxxxx>; <m-watkins@xxxxxx>; 
<nsekhar@xxxxxx>; <sachi@xxxxxxxxxxxxxxxxxxxx>; "Wolfgang Grandegger" 
<wg@xxxxxxxxxxxxxx>; "open list:CAN NETWORK DRIVERS" 
<socketcan-core@xxxxxxxxxxxxxxxx>; "open list:CAN NETWORK DRIVERS" 
<netdev@xxxxxxxxxxxxxxx>; "open list" <linux-kernel@xxxxxxxxxxxxxxx>
Subject: Re: [PATCH v2 09/13] can: pruss CAN driver.

> Hi,
>
> I looked a bit at the TX path:
>
> On Fri, Feb 11, 2011 at 08:21:28PM +0530, Subhasish Ghosh wrote:
> > +static int omapl_pru_can_set_bittiming(struct net_device *ndev)
> > +{
> > + struct omapl_pru_can_priv *priv = netdev_priv(ndev);
> > + struct can_bittiming *bt = &priv->can.bittiming;
> > + long bit_error = 0;
> > +
> > + if (priv->can.ctrlmode & CAN_CTRLMODE_3_SAMPLES) {
> > + dev_warn(priv->dev, "WARN: Triple"
> > + "sampling not set due to h/w limitations");
> You should not have enabled CAN_CTRLMODE_3_SAMPLES in the first place?

SG - Ok Will remove.
> > + }
> > + if (pru_can_calc_timing(priv->dev, priv->can.clock.freq,
> > + bt->bitrate) != 0)
> > + return -EINVAL;
> > + bit_error =
> > +     (((priv->timer_freq / (priv->timer_freq / bt->bitrate)) -
> > +       bt->bitrate) * 1000) / bt->bitrate;
> > + if (bit_error) {
> > + bit_error =
> > +     (((priv->timer_freq / (priv->timer_freq / bt->bitrate)) -
> > +       bt->bitrate) * 1000000) / bt->bitrate;
> > + printk(KERN_INFO "\nBitrate error %ld.%ld%%\n",
> > + bit_error / 10000, bit_error % 1000);
> > + } else
> > + printk(KERN_INFO "\nBitrate error 0.0%%\n");
> > +
> > + return 0;
> > +}
> I wonder how much of this code is duplicated from drivers/net/can/dev.c ?
SG - Well, I just followed ti_hecc.c :-)

> > +static netdev_tx_t omapl_pru_can_start_xmit(struct sk_buff *skb,
> > +     struct net_device *ndev)
> > +{
> > + struct omapl_pru_can_priv *priv = netdev_priv(ndev);
> > + struct can_frame *cf = (struct can_frame *)skb->data;
> > + int count;
> > + u8 *data = cf->data;
> > + u8 dlc = cf->can_dlc;
> > + u8 *ptr8data = NULL;
> > +
> most drivers start with:
> if (can_dropped_invalid_skb(dev, skb))
> return NETDEV_TX_OK;

SG - Will do.
> > + netif_stop_queue(ndev);
> why would you stop when you just resumed the queue?

SG - I do not want more than one transmit request at one time. Hence, on 
entering the transmit
I am using netif_stop_queue to disable tx.

> > + if (cf->can_id & CAN_EFF_FLAG) /* Extended frame format */
> > + *((u32 *) &priv->can_tx_hndl.strcanmailbox) =
> > +     (cf->can_id & CAN_EFF_MASK) | PRU_CANMID_IDE;
> > + else /* Standard frame format */
> > + *((u32 *) &priv->can_tx_hndl.strcanmailbox) =
> > +     (cf->can_id & CAN_SFF_MASK) << 18;
> > +
> > + if (cf->can_id & CAN_RTR_FLAG) /* Remote transmission request */
> > + *((u32 *) &priv->can_tx_hndl.strcanmailbox) |= CAN_RTR_FLAG;
> > +
> > + ptr8data = &priv->can_tx_hndl.strcanmailbox.u8data7 + (dlc - 1);
> > + for (count = 0; count < (u8) dlc; count++) {
> > + *ptr8data-- = *data++;
> > + }
> > + *((u32 *) &priv->can_tx_hndl.strcanmailbox.u16datalength) = (u32) dlc;
> > +/*
> > + * search for the next available mbx
> > + * if the next mbx is busy, then try the next + 1
> > + * do this until the head is reached.
> > + * if still unable to tx, stop accepting any packets
> > + * if able to tx and the head is reached, then reset next to tail, i.e 
> > mbx0
> > + * if head is not reached, then just point to the next mbx
> > + */
> > + for (; priv->tx_next <= priv->tx_head; priv->tx_next++) {
> > + priv->can_tx_hndl.ecanmailboxnumber =
> > +     (can_mailbox_number) priv->tx_next;
> > + if (-1 == pru_can_write_data_to_mailbox(priv->dev,
> > + &priv->can_tx_hndl)) {
> > + if (priv->tx_next == priv->tx_head) {
> > + priv->tx_next = priv->tx_tail;
> > + if (!netif_queue_stopped(ndev))
> If you get here, the queue is not stopped. This test is therefore useless.

SG -Ok, will remove
> > + netif_stop_queue(ndev); /* IF stalled */
> > + dev_err(priv->dev,
> > + "%s: no tx mbx available", __func__);
> > + return NETDEV_TX_BUSY;
> > + } else
> > + continue;
> > + } else {
> > + /* set transmit request */
> > + pru_can_tx(priv->dev, priv->tx_next, CAN_TX_PRU_1);
> > + pru_can_tx_mode_set(priv->dev, false, ecanreceive);
> > + pru_can_tx_mode_set(priv->dev, true, ecantransmit);
> > + pru_can_start_abort_tx(priv->dev, PRU_CAN_START);
> > + priv->tx_next++;
> > + can_put_echo_skb(skb, ndev, 0);
> > + break;
> > + }
> > + }
> > + if (priv->tx_next > priv->tx_head) {
> > + priv->tx_next = priv->tx_tail;
> > + }
> > + return NETDEV_TX_OK;
> > +}
> > +
> > +
>
> > +irqreturn_t omapl_tx_can_intr(int irq, void *dev_id)
> > +{
> > + struct net_device *ndev = dev_id;
> > + struct omapl_pru_can_priv *priv = netdev_priv(ndev);
> > + struct net_device_stats *stats = &ndev->stats;
> > + u32 bit_set, mbxno;
> > +
> > + pru_can_get_intr_status(priv->dev, &priv->can_tx_hndl);
> > + if ((PRU_CAN_ISR_BIT_CCI & priv->can_tx_hndl.u32interruptstatus)
> > +     || (PRU_CAN_ISR_BIT_SRDI & priv->can_tx_hndl.u32interruptstatus)) {
> > + __can_debug("tx_int_status = 0x%X\n",
> > +     priv->can_tx_hndl.u32interruptstatus);
> > + can_free_echo_skb(ndev, 0);
> > + } else {
> > + for (bit_set = 0; ((priv->can_tx_hndl.u32interruptstatus & 0xFF)
> > + >> bit_set != 0); bit_set++)
> > + ;
> > + if (0 == bit_set) {
> > + __can_err("%s: invalid mailbox number\n", __func__);
> > + can_free_echo_skb(ndev, 0);
> > + } else {
> > + mbxno = bit_set - 1; /* mail box numbering starts from 0 */
> > + if (PRU_CAN_ISR_BIT_ESI & priv->can_tx_hndl.
> > +     u32interruptstatus) {
> > + /* read gsr and ack pru */
> > + pru_can_get_global_status(priv->dev, &priv->can_tx_hndl);
> > + omapl_pru_can_err(ndev,
> > +   priv->can_tx_hndl.
> > +   u32interruptstatus,
> > +   priv->can_tx_hndl.
> > +   u32globalstatus);
> > + } else {
> > + stats->tx_packets++;
> > + /* stats->tx_bytes += dlc; */
> > + /*can_get_echo_skb(ndev, 0);*/
> > + }
> > + }
> > + }
> > + if (netif_queue_stopped(ndev))
> you can call netif_wake_queue(ndev) multiple times, so there is no need
> for netif_queue_stopped()

SG -Ok, will remove

> > + netif_wake_queue(ndev);
> > +
> > + can_get_echo_skb(ndev, 0);
> > + pru_can_tx_mode_set(priv->dev, true, ecanreceive);
> > + return IRQ_HANDLED;
> > +}
> > +
> > +static int omapl_pru_can_open(struct net_device *ndev)
> > +{
> > + struct omapl_pru_can_priv *priv = netdev_priv(ndev);
> > + int err;
> > +
> > + /* register interrupt handler */
> > + err = request_irq(priv->trx_irq, &omapl_rx_can_intr, IRQF_SHARED,
> > +   "pru_can_irq", ndev);
> you're doing a lot of work _in_ the irq handler. Maybe threaded irq?
SG -Ok, will do

> > +static int omapl_pru_can_close(struct net_device *ndev)
> > +{
> > + struct omapl_pru_can_priv *priv = netdev_priv(ndev);
> > +
> > + if (!netif_queue_stopped(ndev))
> check is not needed.

SG -Ok, will remove

> > + netif_stop_queue(ndev);
> > +
> > + close_candev(ndev);
> > +
> > + free_irq(priv->trx_irq, ndev);
> > + return 0;
> > +}
> > +
>
> Regards,
> Kurt 

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