Re: [PATCH v4 4/5] can: flexcan: put TX mailbox into TX_INACTIVE mode after tx-complete

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 09/16/2014 05:18 PM, David Jander wrote:
> On Tue, 16 Sep 2014 16:20:33 +0200
> Marc Kleine-Budde <mkl@pengutronix.de> wrote:
> 
>> After sending a RTR frame the TX mailbox becomes a RX_EMPTY mailbox. To avoid
>> side effects when the RX-FIFO is full, this patch puts the TX mailbox into
>> TX_INACTIVE mode after the transmission has been completed.
>>
>> Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>
>> ---
>>
>> Changes since v3:
>> - new
>>
>>  drivers/net/can/flexcan.c | 3 +++
>>  1 file changed, 3 insertions(+)
>>
>> diff --git a/drivers/net/can/flexcan.c b/drivers/net/can/flexcan.c
>> index 54061c4..c17ae9e 100644
>> --- a/drivers/net/can/flexcan.c
>> +++ b/drivers/net/can/flexcan.c
>> @@ -765,6 +765,9 @@ static irqreturn_t flexcan_irq(int irq, void *dev_id)
>>  		stats->tx_bytes += can_get_echo_skb(dev, 0);
>>  		stats->tx_packets++;
>>  		can_led_event(dev, CAN_LED_EVENT_TX);
>> +		/* after sending a RTR frame mailbox is in RX mode */
>> +		flexcan_write(FLEXCAN_MB_CODE_TX_INACTIVE,
>> +			      &regs->cantxfg[FLEXCAN_TX_BUF_ID].can_ctrl);
>>  		flexcan_write((1 << FLEXCAN_TX_BUF_ID), &regs->iflag1);
>>  		netif_wake_queue(dev);
>>  	}
> 
> Good one. I hadn't notice that case yet.

Just stumbled over it, the reference manual is a bit vague, it this
mailbox will receive any CAN frame or just a CAN frame with the same ID.

> Since you do this in the IRQ, I assume the expected race-condition window is
> minimal, but AFAICS there is stil a (very) small chance of a race if an

Yes, there's a race window.

> overflow message arrives before this code in the IRQ handler is reached.
> Both chance of occurring and impact is so small that it will not likely be a
> problem ever... besides the fact that it cannot be avoided. Should this be
> mentioned?

Good point, I'll add a comment to the code.

Marc
-- 
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