RE: [PATCH 05/14] net: axienet: Factor out TX descriptor chain cleanup

[Radhey Shyam Pandey]

> -----Original Message-----
> From: Andre Przywara <andre.przywara@xxxxxxx>
> Sent: Friday, January 10, 2020 5:24 PM
> To: David S . Miller <davem@xxxxxxxxxxxxx>; Radhey Shyam Pandey
> <radheys@xxxxxxxxxx>
> Cc: Michal Simek <michals@xxxxxxxxxx>; Robert Hancock
> <hancock@xxxxxxxxxxxxx>; netdev@xxxxxxxxxxxxxxx; linux-arm-
> kernel@xxxxxxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx
> Subject: [PATCH 05/14] net: axienet: Factor out TX descriptor chain cleanup
> 
> Factor out the code that cleans up a number of connected TX descriptors,
> as we will need it to properly roll back a failed _xmit() call.
> There are subtle differences between cleaning up a successfully sent
> chain (unknown number of involved descriptors, total data size needed)
> and a chain that was about to set up (number of descriptors known), so
> cater for those variations with some extra parameters.
> 
> Signed-off-by: Andre Przywara <andre.przywara@xxxxxxx>
> ---
>  .../net/ethernet/xilinx/xilinx_axienet_main.c | 75 ++++++++++++-------
>  1 file changed, 50 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> index ec5d01adc1d5..82abe2b0f16a 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> @@ -543,33 +543,37 @@ static int axienet_device_reset(struct net_device
> *ndev)
>  	return 0;
>  }
> 
> -/**
> - * axienet_start_xmit_done - Invoked once a transmit is completed by the
> - * Axi DMA Tx channel.
> - * @ndev:	Pointer to the net_device structure
> - *
> - * This function is invoked from the Axi DMA Tx isr to notify the completion
> - * of transmit operation. It clears fields in the corresponding Tx BDs and
> - * unmaps the corresponding buffer so that CPU can regain ownership of
> the
> - * buffer. It finally invokes "netif_wake_queue" to restart transmission if
> - * required.
> +/* Clean up a series of linked TX descriptors. Would either be called
> + * after a successful transmit operation, or after there was an error
> + * when setting up the chain.
> + * Returns the number of descriptors handled.
>   */
> -static void axienet_start_xmit_done(struct net_device *ndev)

To be consistent we can add the doxygen function description.
The rest looks good. Feel free to add:
Reviewed-by: Radhey Shyam Pandey <radhey.shyam.pandey@xxxxxxxxxx>

> +static int axienet_free_tx_chain(struct net_device *ndev, u32 first_bd,
> +				 int nr_bds, u32 *sizep)
>  {
> -	u32 size = 0;
> -	u32 packets = 0;
>  	struct axienet_local *lp = netdev_priv(ndev);
> +	int max_bds = (nr_bds != -1) ? nr_bds : lp->tx_bd_num;
>  	struct axidma_bd *cur_p;
> -	unsigned int status = 0;
> +	unsigned int status;
> +	int i;
> +
> +	for (i = 0; i < max_bds; i++) {
> +		cur_p = &lp->tx_bd_v[(first_bd + i) % lp->tx_bd_num];
> +		status = cur_p->status;
> +
> +		/* If no number is given, clean up *all* descriptors that have
> +		 * been completed by the MAC.
> +		 */
> +		if (nr_bds == -1 && !(status &
> XAXIDMA_BD_STS_COMPLETE_MASK))
> +			break;
> 
> -	cur_p = &lp->tx_bd_v[lp->tx_bd_ci];
> -	status = cur_p->status;
> -	while (status & XAXIDMA_BD_STS_COMPLETE_MASK) {
>  		dma_unmap_single(ndev->dev.parent, cur_p->phys,
>  				(cur_p->cntrl &
> XAXIDMA_BD_CTRL_LENGTH_MASK),
>  				DMA_TO_DEVICE);
> -		if (cur_p->skb)
> +
> +		if (cur_p->skb && (status &
> XAXIDMA_BD_STS_COMPLETE_MASK))
>  			dev_consume_skb_irq(cur_p->skb);
> +
>  		cur_p->cntrl = 0;
>  		cur_p->app0 = 0;
>  		cur_p->app1 = 0;
> @@ -578,15 +582,36 @@ static void axienet_start_xmit_done(struct
> net_device *ndev)
>  		cur_p->status = 0;
>  		cur_p->skb = NULL;
> 
> -		size += status & XAXIDMA_BD_STS_ACTUAL_LEN_MASK;
> -		packets++;
> -
> -		if (++lp->tx_bd_ci >= lp->tx_bd_num)
> -			lp->tx_bd_ci = 0;
> -		cur_p = &lp->tx_bd_v[lp->tx_bd_ci];
> -		status = cur_p->status;
> +		if (sizep)
> +			*sizep += status &
> XAXIDMA_BD_STS_ACTUAL_LEN_MASK;
>  	}
> 
> +	return i;
> +}
> +
> +/**
> + * axienet_start_xmit_done - Invoked once a transmit is completed by the
> + * Axi DMA Tx channel.
> + * @ndev:	Pointer to the net_device structure
> + *
> + * This function is invoked from the Axi DMA Tx isr to notify the completion
> + * of transmit operation. It clears fields in the corresponding Tx BDs and
> + * unmaps the corresponding buffer so that CPU can regain ownership of
> the
> + * buffer. It finally invokes "netif_wake_queue" to restart transmission if
> + * required.
> + */
> +static void axienet_start_xmit_done(struct net_device *ndev)
> +{
> +	u32 size = 0;
> +	u32 packets = 0;
> +	struct axienet_local *lp = netdev_priv(ndev);
> +
> +	packets = axienet_free_tx_chain(ndev, lp->tx_bd_ci, -1, &size);
> +
> +	lp->tx_bd_ci += packets;
> +	if (lp->tx_bd_ci >= lp->tx_bd_num)
> +		lp->tx_bd_ci -= lp->tx_bd_num;
> +
>  	ndev->stats.tx_packets += packets;
>  	ndev->stats.tx_bytes += size;
> 
> --
> 2.17.1