netdev - Re: [PATCH net v2 1/2] dpaa_eth: update the buffer layout for non-A050385 erratum scenarios

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Date:   Fri, 30 Oct 2020 18:41:03 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Camelia Groza <camelia.groza@....com>
Cc:     willemdebruijn.kernel@...il.com, madalin.bucur@....nxp.com,
        davem@...emloft.net, netdev@...r.kernel.org
Subject: Re: [PATCH net v2 1/2] dpaa_eth: update the buffer layout for
 non-A050385 erratum scenarios

On Wed, 28 Oct 2020 18:40:59 +0200 Camelia Groza wrote:
> Impose a large RX private data area only when the A050385 erratum is
> present on the hardware. A smaller buffer size is sufficient in all
> other scenarios. This enables a wider range of linear frame sizes
> in non-erratum scenarios

Any word on user impact? Measurable memory waste?

> Fixes: 3c68b8fffb48 ("dpaa_eth: FMan erratum A050385 workaround")
> Signed-off-by: Camelia Groza <camelia.groza@....com>
> ---
>  drivers/net/ethernet/freescale/dpaa/dpaa_eth.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> index 06cc863..1aac0b6 100644
> --- a/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> +++ b/drivers/net/ethernet/freescale/dpaa/dpaa_eth.c
> @@ -175,8 +175,10 @@
>  #define DPAA_TIME_STAMP_SIZE 8
>  #define DPAA_HASH_RESULTS_SIZE 8
>  #ifdef CONFIG_DPAA_ERRATUM_A050385
> -#define DPAA_RX_PRIV_DATA_SIZE (DPAA_A050385_ALIGN - (DPAA_PARSE_RESULTS_SIZE\
> -	 + DPAA_TIME_STAMP_SIZE + DPAA_HASH_RESULTS_SIZE))
> +#define DPAA_RX_PRIV_DATA_SIZE (fman_has_errata_a050385() ? \
> +			(DPAA_A050385_ALIGN - (DPAA_PARSE_RESULTS_SIZE\
> +			 + DPAA_TIME_STAMP_SIZE + DPAA_HASH_RESULTS_SIZE)) : \
> +			(DPAA_TX_PRIV_DATA_SIZE + dpaa_rx_extra_headroom))

This expressions is highly unreadable, please refactor. Maybe separate
defines for errata and non-errata, and one for the ternary operator?

>  #else
>  #define DPAA_RX_PRIV_DATA_SIZE	(u16)(DPAA_TX_PRIV_DATA_SIZE + \
>  					dpaa_rx_extra_headroom)