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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 06/14] net: axienet: Check for DMA mapping errors
Thread-Topic: [PATCH 06/14] net: axienet: Check for DMA mapping errors
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Date:   Mon, 13 Jan 2020 05:54:42 +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 06/14] net: axienet: Check for DMA mapping errors
>=20
> Especially with the default 32-bit DMA mask, DMA buffers are a limited
> resource, so their allocation can fail.
> So as the DMA API documentation requires, add error checking code after
> dma_map_single() calls to catch the case where we run out of "low" memory=
.
>=20
> Signed-off-by: Andre Przywara <andre.przywara@arm.com>
> ---
>  .../net/ethernet/xilinx/xilinx_axienet_main.c | 22 ++++++++++++++++++-
>  1 file changed, 21 insertions(+), 1 deletion(-)
>=20
> diff --git a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> index 82abe2b0f16a..8d2b67cbecf9 100644
> --- a/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> +++ b/drivers/net/ethernet/xilinx/xilinx_axienet_main.c
> @@ -248,6 +248,11 @@ static int axienet_dma_bd_init(struct net_device
> *ndev)
>  						     skb->data,
>  						     lp->max_frm_size,
>  						     DMA_FROM_DEVICE);
> +		if (dma_mapping_error(ndev->dev.parent, lp->rx_bd_v[i].phys))

Prefer using unlikely compiler hint for dma_mapping_error.=20
Also, we need to add error print to report this condition to the user,
in case it isn't there in dma_mapping_error implementation.

> {
> +			dev_kfree_skb(skb);

free of skb is already handled in _release. We can reuse that?
> +			goto out;
> +		}
> +
>  		lp->rx_bd_v[i].cntrl =3D lp->max_frm_size;
>  	}
>=20
> @@ -668,6 +673,7 @@ axienet_start_xmit(struct sk_buff *skb, struct
> net_device *ndev)
>  	dma_addr_t tail_p;
>  	struct axienet_local *lp =3D netdev_priv(ndev);
>  	struct axidma_bd *cur_p;
> +	u32 orig_tail_ptr =3D lp->tx_bd_tail;
>=20
>  	num_frag =3D skb_shinfo(skb)->nr_frags;
>  	cur_p =3D &lp->tx_bd_v[lp->tx_bd_tail];
> @@ -703,9 +709,11 @@ axienet_start_xmit(struct sk_buff *skb, struct
> net_device *ndev)
>  		cur_p->app0 |=3D 2; /* Tx Full Checksum Offload Enabled */
>  	}
>=20
> -	cur_p->cntrl =3D skb_headlen(skb) | XAXIDMA_BD_CTRL_TXSOF_MASK;
>  	cur_p->phys =3D dma_map_single(ndev->dev.parent, skb->data,
>  				     skb_headlen(skb), DMA_TO_DEVICE);
> +	if (dma_mapping_error(ndev->dev.parent, cur_p->phys))
> +		return NETDEV_TX_BUSY;

This is not ideally tx busy and related to available mem mapping in the sys=
tem.=20
I just looked at other eth drivers and it seems they return TX_OK with drop
count stats incremented.

> +	cur_p->cntrl =3D skb_headlen(skb) | XAXIDMA_BD_CTRL_TXSOF_MASK;
>=20
>  	for (ii =3D 0; ii < num_frag; ii++) {
>  		if (++lp->tx_bd_tail >=3D lp->tx_bd_num) @@ -716,6 +724,13 @@
> axienet_start_xmit(struct sk_buff *skb, struct net_device *ndev)
>  					     skb_frag_address(frag),
>  					     skb_frag_size(frag),
>  					     DMA_TO_DEVICE);
> +		if (dma_mapping_error(ndev->dev.parent, cur_p->phys)) {
> +			axienet_free_tx_chain(ndev, orig_tail_ptr, ii + 1,
> +					      NULL);
> +			lp->tx_bd_tail =3D orig_tail_ptr;
> +
> +			return NETDEV_TX_BUSY;
> +		}
>  		cur_p->cntrl =3D skb_frag_size(frag);
>  	}
>=20
> @@ -796,6 +811,11 @@ static void axienet_recv(struct net_device *ndev)
>  		cur_p->phys =3D dma_map_single(ndev->dev.parent, new_skb-
> >data,
>  					     lp->max_frm_size,
>  					     DMA_FROM_DEVICE);
> +		if (dma_mapping_error(ndev->dev.parent, cur_p->phys)) {
> +			dev_kfree_skb(new_skb);
> +			return;
> +		}
> +
>  		cur_p->cntrl =3D lp->max_frm_size;
>  		cur_p->status =3D 0;
>  		cur_p->skb =3D new_skb;
> --
> 2.17.1