netdev - Re: [PATCH net 2/3] dpaa_eth: reduce data alignment requirements for the A050385 erratum

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Message-ID: <20210204155803.GC2580@ranger.igk.intel.com>
Date:   Thu, 4 Feb 2021 16:58:03 +0100
From:   Maciej Fijalkowski <maciej.fijalkowski@...el.com>
To:     Camelia Groza <camelia.groza@....com>
Cc:     kuba@...nel.org, davem@...emloft.net, madalin.bucur@....nxp.com,
        netdev@...r.kernel.org
Subject: Re: [PATCH net 2/3] dpaa_eth: reduce data alignment requirements for
 the A050385 erratum

On Tue, Feb 02, 2021 at 07:34:43PM +0200, Camelia Groza wrote:
> The 256 byte data alignment is required for preventing DMA transaction
> splits when crossing 4K page boundaries. Since XDP deals only with page
> sized buffers or less, this restriction isn't needed. Instead, the data
> only needs to be aligned to 64 bytes to prevent DMA transaction splits.
> 
> These lessened restrictions can increase performance by widening the pool
> of permitted data alignments and preventing unnecessary realignments.
> 
> Fixes: ae680bcbd06a ("dpaa_eth: implement the A050385 erratum workaround for XDP")
> Signed-off-by: Camelia Groza <camelia.groza@....com>

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

> ---
>  drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> index e1d041c35ad9..78dfa05f6d55 100644
> --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> @@ -2192,7 +2192,7 @@ static int dpaa_a050385_wa_xdpf(struct dpaa_priv *priv,
>  	 * byte frame headroom. If the XDP program uses all of it, copy the
>  	 * data to a new buffer and make room for storing the backpointer.
>  	 */
> -	if (PTR_IS_ALIGNED(xdpf->data, DPAA_A050385_ALIGN) &&
> +	if (PTR_IS_ALIGNED(xdpf->data, DPAA_FD_DATA_ALIGNMENT) &&
>  	    xdpf->headroom >= priv->tx_headroom) {
>  		xdpf->headroom = priv->tx_headroom;
>  		return 0;
> -- 
> 2.17.1
>