linux-kernel - Re: [PATCH] net: macb: restart tx after tx used bit read

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Date:   Fri, 7 Dec 2018 13:10:48 +0000
From:   <Claudiu.Beznea@...rochip.com>
To:     <Nicolas.Ferre@...rochip.com>, <davem@...emloft.net>
CC:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] net: macb: restart tx after tx used bit read

Hi David,

Please ignore this one for the moment, I'll have to run few more tests on it.

Thank you,
Claudiu Beznea

On 06.12.2018 19:44, Claudiu Beznea - M18063 wrote:
> From: Claudiu Beznea <claudiu.beznea@...rochip.com>
> 
> On some platforms (currently detected only on SAMA5D4) TX might stuck
> even the pachets are still present in DMA memories and TX start was
> issued for them. This happens due to race condition between MACB driver
> updating next TX buffer descriptor to be used and IP reading the same
> descriptor. In such a case, the "TX USED BIT READ" interrupt is asserted.
> GEM/MACB user guide specifies that if a "TX USED BIT READ" interrupt
> is asserted TX must be restarted. Restart TX if used bit is read and
> packets are present in software TX queue. Packets are removed from software
> TX queue if TX was successful for them (see macb_tx_interrupt()).
> 
> Signed-off-by: Claudiu Beznea <claudiu.beznea@...rochip.com>
> ---
>  drivers/net/ethernet/cadence/macb_main.c | 21 ++++++++++++++++++++-
>  1 file changed, 20 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 1d86b4d5645a..f920230386ee 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -61,7 +61,8 @@
>  #define MACB_TX_ERR_FLAGS	(MACB_BIT(ISR_TUND)			\
>  					| MACB_BIT(ISR_RLE)		\
>  					| MACB_BIT(TXERR))
> -#define MACB_TX_INT_FLAGS	(MACB_TX_ERR_FLAGS | MACB_BIT(TCOMP))
> +#define MACB_TX_INT_FLAGS	(MACB_TX_ERR_FLAGS | MACB_BIT(TCOMP)	\
> +					| MACB_BIT(TXUBR))
>  
>  /* Max length of transmit frame must be a multiple of 8 bytes */
>  #define MACB_TX_LEN_ALIGN	8
> @@ -1312,6 +1313,21 @@ static void macb_hresp_error_task(unsigned long data)
>  	netif_tx_start_all_queues(dev);
>  }
>  
> +inline static void macb_tx_restart(struct macb_queue *queue)
> +{
> +	unsigned int head = queue->tx_head;
> +	unsigned int tail = queue->tx_tail;
> +	struct macb *bp = queue->bp;
> +
> +	if (bp->caps & MACB_CAPS_ISR_CLEAR_ON_WRITE)
> +		queue_writel(queue, ISR, MACB_BIT(TXUBR));
> +
> +	if (head == tail)
> +		return;
> +
> +	macb_writel(bp, NCR, macb_readl(bp, NCR) | MACB_BIT(TSTART));
> +}
> +
>  static irqreturn_t macb_interrupt(int irq, void *dev_id)
>  {
>  	struct macb_queue *queue = dev_id;
> @@ -1369,6 +1385,9 @@ static irqreturn_t macb_interrupt(int irq, void *dev_id)
>  		if (status & MACB_BIT(TCOMP))
>  			macb_tx_interrupt(queue);
>  
> +		if (status & MACB_BIT(TXUBR))
> +			macb_tx_restart(queue);
> +
>  		/* Link change detection isn't possible with RMII, so we'll
>  		 * add that if/when we get our hands on a full-blown MII PHY.
>  		 */
>