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From:   Radhey Shyam Pandey <radheys@xilinx.com>
To:     Andre Przywara <andre.przywara@arm.com>,
        "David S . Miller" <davem@davemloft.net>
CC:     Michal Simek <michals@xilinx.com>,
        Robert Hancock <hancock@sedsystems.ca>,
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        <linux-arm-kernel@lists.infradead.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH 05/14] net: axienet: Factor out TX descriptor chain
 cleanup
Thread-Topic: [PATCH 05/14] net: axienet: Factor out TX descriptor chain
 cleanup
Thread-Index: AQHVx6y4/M+QpndI/06Wqu2OHMXL/6fkL3TQ
Date:   Fri, 10 Jan 2020 18:04:57 +0000
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> -----Original Message-----
> From: Andre Przywara <andre.przywara@arm.com>
> Sent: Friday, January 10, 2020 5:24 PM
> To: David S . Miller <davem@davemloft.net>; Radhey Shyam Pandey
> <radheys@xilinx.com>
> Cc: Michal Simek <michals@xilinx.com>; Robert Hancock
> <hancock@sedsystems.ca>; netdev@vger.kernel.org; linux-arm-
> kernel@lists.infradead.org; linux-kernel@vger.kernel.org
> Subject: [PATCH 05/14] net: axienet: Factor out TX descriptor chain clean=
up
>=20
> 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.
>=20
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
>  .../net/ethernet/xilinx/xilinx_axienet_main.c | 75 ++++++++++++-------
>  1 file changed, 50 insertions(+), 25 deletions(-)
>=20
> 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;
>  }
>=20
> -/**
> - * 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 comple=
tion
> - * of transmit operation. It clears fields in the corresponding Tx BDs a=
nd
> - * 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@xilinx.com>

> +static int axienet_free_tx_chain(struct net_device *ndev, u32 first_bd,
> +				 int nr_bds, u32 *sizep)
>  {
> -	u32 size =3D 0;
> -	u32 packets =3D 0;
>  	struct axienet_local *lp =3D netdev_priv(ndev);
> +	int max_bds =3D (nr_bds !=3D -1) ? nr_bds : lp->tx_bd_num;
>  	struct axidma_bd *cur_p;
> -	unsigned int status =3D 0;
> +	unsigned int status;
> +	int i;
> +
> +	for (i =3D 0; i < max_bds; i++) {
> +		cur_p =3D &lp->tx_bd_v[(first_bd + i) % lp->tx_bd_num];
> +		status =3D cur_p->status;
> +
> +		/* If no number is given, clean up *all* descriptors that have
> +		 * been completed by the MAC.
> +		 */
> +		if (nr_bds =3D=3D -1 && !(status &
> XAXIDMA_BD_STS_COMPLETE_MASK))
> +			break;
>=20
> -	cur_p =3D &lp->tx_bd_v[lp->tx_bd_ci];
> -	status =3D 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 =3D 0;
>  		cur_p->app0 =3D 0;
>  		cur_p->app1 =3D 0;
> @@ -578,15 +582,36 @@ static void axienet_start_xmit_done(struct
> net_device *ndev)
>  		cur_p->status =3D 0;
>  		cur_p->skb =3D NULL;
>=20
> -		size +=3D status & XAXIDMA_BD_STS_ACTUAL_LEN_MASK;
> -		packets++;
> -
> -		if (++lp->tx_bd_ci >=3D lp->tx_bd_num)
> -			lp->tx_bd_ci =3D 0;
> -		cur_p =3D &lp->tx_bd_v[lp->tx_bd_ci];
> -		status =3D cur_p->status;
> +		if (sizep)
> +			*sizep +=3D status &
> XAXIDMA_BD_STS_ACTUAL_LEN_MASK;
>  	}
>=20
> +	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 comple=
tion
> + * of transmit operation. It clears fields in the corresponding Tx BDs a=
nd
> + * 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 =3D 0;
> +	u32 packets =3D 0;
> +	struct axienet_local *lp =3D netdev_priv(ndev);
> +
> +	packets =3D axienet_free_tx_chain(ndev, lp->tx_bd_ci, -1, &size);
> +
> +	lp->tx_bd_ci +=3D packets;
> +	if (lp->tx_bd_ci >=3D lp->tx_bd_num)
> +		lp->tx_bd_ci -=3D lp->tx_bd_num;
> +
>  	ndev->stats.tx_packets +=3D packets;
>  	ndev->stats.tx_bytes +=3D size;
>=20
> --
> 2.17.1