Re: [PATCH 1/2] pch_can: Stop netif queue if last message buffer is filled

[Alexander Stein <alexander.stein@systec-electronic.com>]

Hello Wolfgang,

Am Dienstag, 21. Februar 2012, 17:25:57 schrieb Wolfgang Grandegger:
> Hi Alexander,
> 
> On 02/21/2012 05:00 PM, Alexander Stein wrote:
> > If all Tx buffers are empty and we start queuing frames (more than Tx
> > buffer size) beginning at the last message buffer we will override the
> > first inserted entry if it doesn't get sent meanwhile, e.g. low priority
> > or ACK error. There is no stop condition when all buffers are used.
> > We will get get awoken by pch_can_tx_complete when the last entry is sent.
> > 
> > Signed-off-by: Alexander Stein <alexander.stein@systec-electronic.com>
> > ---
> >  drivers/net/can/pch_can.c |    4 +---
> >  1 files changed, 1 insertions(+), 3 deletions(-)
> > 
> > diff --git a/drivers/net/can/pch_can.c b/drivers/net/can/pch_can.c
> > index 6edc25e..3af5341 100644
> > --- a/drivers/net/can/pch_can.c
> > +++ b/drivers/net/can/pch_can.c
> > @@ -903,9 +903,7 @@ static netdev_tx_t pch_xmit(struct sk_buff *skb, struct net_device *ndev)
> >  
> >  	tx_obj_no = priv->tx_obj;
> >  	if (priv->tx_obj == PCH_TX_OBJ_END) {
> > -		if (ioread32(&priv->regs->treq2) & PCH_TREQ2_TX_MASK)
> > -			netif_stop_queue(ndev);
> > -
> > +		netif_stop_queue(ndev);
> >  		priv->tx_obj = PCH_TX_OBJ_START;
> >  	} else {
> >  		priv->tx_obj++;
> 
> The pch_can uses a C_CAN core (and for maintenance reasons we would like
> to get ride of it sooner than later). In that driver the queue is
> stopped here:
> 
> http://lxr.linux.no/#linux+v3.2.7/drivers/net/can/c_can/c_can.c#L508

Does the C_CAN core have a real fifo? The message "fifo" in PCH CAN just uses the first message object. So you will reorder message under some conditions if used like a real fifo.

> Therefore I'm not sure if your fix is enough (without looking into the
> manual). I could send you a "pch_pci" driver patch for C_CAN, which
> would allow you to use it. What kernel version are you using?

We are currently using 2.6.39.

Best regards,
Alexander
-- 
Dipl.-Inf. Alexander Stein

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