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Date:   Thu, 23 Jul 2020 11:32:00 -0500
From:   Thor Thayer <thor.thayer@...ux.intel.com>
To:     "Ooi, Joyce" <joyce.ooi@...el.com>,
        "David S . Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>
Cc:     netdev@...r.kernel.org, linux-kernel@...r.kernel.org,
        Dalon Westergreen <dalon.westergreen@...ux.intel.com>,
        Tan Ley Foon <ley.foon.tan@...el.com>,
        See Chin Liang <chin.liang.see@...el.com>,
        Dinh Nguyen <dinh.nguyen@...el.com>,
        Dalon Westergreen <dalon.westergreen@...el.com>
Subject: Re: [PATCH v4 01/10] net: eth: altera: tse_start_xmit ignores
 tx_buffer call response

On 7/8/20 2:23 AM, Ooi, Joyce wrote:
> From: Dalon Westergreen <dalon.westergreen@...el.com>
> 
> The return from tx_buffer call in tse_start_xmit is
> inapropriately ignored.  tse_buffer calls should return
> 0 for success or NETDEV_TX_BUSY.  tse_start_xmit should
> return not report a successful transmit when the tse_buffer
> call returns an error condition.
> 
> In addition to the above, the msgdma and sgdma do not return
> the same value on success or failure.  The sgdma_tx_buffer
> returned 0 on failure and a positive number of transmitted
> packets on success.  Given that it only ever sends 1 packet,
> this made no sense.  The msgdma implementation msgdma_tx_buffer
> returns 0 on success.
> 
>    -> Don't ignore the return from tse_buffer calls
>    -> Fix sgdma tse_buffer call to return 0 on success
>       and NETDEV_TX_BUSY on failure.
> 
> Signed-off-by: Dalon Westergreen <dalon.westergreen@...el.com>
> Signed-off-by: Joyce Ooi <joyce.ooi@...el.com>
> ---
> v2: no change
> v3: queue is stopped before returning NETDEV_TX_BUSY
> v4: no change
> ---
>   drivers/net/ethernet/altera/altera_sgdma.c    | 19 ++++++++++++-------
>   drivers/net/ethernet/altera/altera_tse_main.c |  4 +++-
>   2 files changed, 15 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/net/ethernet/altera/altera_sgdma.c b/drivers/net/ethernet/altera/altera_sgdma.c
> index db97170da8c7..fe6276c7e4a3 100644
> --- a/drivers/net/ethernet/altera/altera_sgdma.c
> +++ b/drivers/net/ethernet/altera/altera_sgdma.c
> @@ -4,6 +4,7 @@
>    */
>   
>   #include <linux/list.h>
> +#include <linux/netdevice.h>
>   #include "altera_utils.h"
>   #include "altera_tse.h"
>   #include "altera_sgdmahw.h"
> @@ -159,10 +160,11 @@ void sgdma_clear_txirq(struct altera_tse_private *priv)
>   		    SGDMA_CTRLREG_CLRINT);
>   }
>   
> -/* transmits buffer through SGDMA. Returns number of buffers
> - * transmitted, 0 if not possible.
> - *
> - * tx_lock is held by the caller
> +/* transmits buffer through SGDMA.
> + *   original behavior returned the number of transmitted packets (always 1) &
> + *   returned 0 on error.  This differs from the msgdma.  the calling function
> + *   will now actually look at the code, so from now, 0 is good and return
> + *   NETDEV_TX_BUSY when busy.
>    */
>   int sgdma_tx_buffer(struct altera_tse_private *priv, struct tse_buffer *buffer)
>   {
> @@ -173,8 +175,11 @@ int sgdma_tx_buffer(struct altera_tse_private *priv, struct tse_buffer *buffer)
>   	struct sgdma_descrip __iomem *ndesc = &descbase[1];
>   
>   	/* wait 'til the tx sgdma is ready for the next transmit request */
> -	if (sgdma_txbusy(priv))
> -		return 0;
> +	if (sgdma_txbusy(priv)) {
> +		if (!netif_queue_stopped(priv->dev))
> +			netif_stop_queue(priv->dev);
> +		return NETDEV_TX_BUSY;
> +	}
>   
>   	sgdma_setup_descrip(cdesc,			/* current descriptor */
>   			    ndesc,			/* next descriptor */
> @@ -191,7 +196,7 @@ int sgdma_tx_buffer(struct altera_tse_private *priv, struct tse_buffer *buffer)
>   	/* enqueue the request to the pending transmit queue */
>   	queue_tx(priv, buffer);
>   
> -	return 1;
> +	return 0;
>   }
>   
>   
> diff --git a/drivers/net/ethernet/altera/altera_tse_main.c b/drivers/net/ethernet/altera/altera_tse_main.c
> index 907125abef2c..ec2b36e05c3f 100644
> --- a/drivers/net/ethernet/altera/altera_tse_main.c
> +++ b/drivers/net/ethernet/altera/altera_tse_main.c
> @@ -595,7 +595,9 @@ static netdev_tx_t tse_start_xmit(struct sk_buff *skb, struct net_device *dev)
>   	buffer->dma_addr = dma_addr;
>   	buffer->len = nopaged_len;
>   
> -	priv->dmaops->tx_buffer(priv, buffer);
> +	ret = priv->dmaops->tx_buffer(priv, buffer);
> +	if (ret)
> +		goto out;
>   
>   	skb_tx_timestamp(skb);
>   
> 
Reviewed-by: Thor Thayer <thor.thayer@...ux.intel.com>

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