Re: [PATCH net 3/3] dpaa_eth: try to move the data in place for the A050385 erratum

[Maciej Fijalkowski <maciej.fijalkowski@intel.com>]

On Tue, Feb 02, 2021 at 07:34:44PM +0200, Camelia Groza wrote:
> The XDP frame's headroom might be large enough to accommodate the
> xdpf backpointer as well as shifting the data to an aligned address.
> 
> Try this first before resorting to allocating a new buffer and copying
> the data.
> 
> Suggested-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>
> Signed-off-by: Camelia Groza <camelia.groza@nxp.com>

Acked-by: Maciej Fijalkowski <maciej.fijalkowski@intel.com>

> ---
>  .../net/ethernet/freescale/dpaa/dpaa_eth.c    | 20 ++++++++++++++++++-
>  1 file changed, 19 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> index 78dfa05f6d55..d093b56dc30f 100644
> --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> @@ -2180,8 +2180,9 @@ static int dpaa_a050385_wa_xdpf(struct dpaa_priv *priv,
>  				struct xdp_frame **init_xdpf)
>  {
>  	struct xdp_frame *new_xdpf, *xdpf = *init_xdpf;
> -	void *new_buff;
> +	void *new_buff, *aligned_data;
>  	struct page *p;
> +	u32 data_shift;
>  	int headroom;
>  
>  	/* Check the data alignment and make sure the headroom is large
> @@ -2198,6 +2199,23 @@ static int dpaa_a050385_wa_xdpf(struct dpaa_priv *priv,
>  		return 0;
>  	}
>  
> +	/* Try to move the data inside the buffer just enough to align it and
> +	 * store the xdpf backpointer. If the available headroom isn't large
> +	 * enough, resort to allocating a new buffer and copying the data.
> +	 */
> +	aligned_data = PTR_ALIGN_DOWN(xdpf->data, DPAA_FD_DATA_ALIGNMENT);
> +	data_shift = xdpf->data - aligned_data;
> +
> +	/* The XDP frame's headroom needs to be large enough to accommodate
> +	 * shifting the data as well as storing the xdpf backpointer.
> +	 */
> +	if (xdpf->headroom  >= data_shift + priv->tx_headroom) {
> +		memmove(aligned_data, xdpf->data, xdpf->len);
> +		xdpf->data = aligned_data;
> +		xdpf->headroom = priv->tx_headroom;
> +		return 0;
> +	}
> +
>  	/* The new xdp_frame is stored in the new buffer. Reserve enough space
>  	 * in the headroom for storing it along with the driver's private
>  	 * info. The headroom needs to be aligned to DPAA_FD_DATA_ALIGNMENT to
> -- 
> 2.17.1
>