Re: [PATCH 2/2] net: macb: Limit maximum GEM TX length in TSO

[<Claudiu.Beznea@microchip.com>]

On 31.01.2020 12:27, Harini Katakam wrote:
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> 
> GEM_MAX_TX_LEN currently resolves to 0x3FF8 for any IP version supporting
> TSO with full 14bits of length field in payload descriptor. But an IP
> errata causes false amba_error (bit 6 of ISR) when length in payload
> descriptors is specified above 16387. The error occurs because the DMA
> falsely concludes that there is not enough space in SRAM for incoming
> payload. These errors were observed continuously under stress of large
> packets using iperf on a version where SRAM was 16K for each queue. This
> errata will be documented shortly and affects all versions since TSO
> functionality was added. Hence limit the max length to 0x3FC0 (rounded).
> 
> Signed-off-by: Harini Katakam <harini.katakam@xilinx.com>
> ---
>  drivers/net/ethernet/cadence/macb_main.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/net/ethernet/cadence/macb_main.c b/drivers/net/ethernet/cadence/macb_main.c
> index 2e418b8..994fe67 100644
> --- a/drivers/net/ethernet/cadence/macb_main.c
> +++ b/drivers/net/ethernet/cadence/macb_main.c
> @@ -74,6 +74,7 @@ struct sifive_fu540_macb_mgmt {
>  #define MACB_TX_LEN_ALIGN      8
>  #define MACB_MAX_TX_LEN                ((unsigned int)((1 << MACB_TX_FRMLEN_SIZE) - 1) & ~((unsigned int)(MACB_TX_LEN_ALIGN - 1)))
>  #define GEM_MAX_TX_LEN         ((unsigned int)((1 << GEM_TX_FRMLEN_SIZE) - 1) & ~((unsigned int)(MACB_TX_LEN_ALIGN - 1)))
> +#define GEM_MAX_TX_LEN_ERRATA  (unsigned int)(0x3FC0)
> 
>  #define GEM_MTU_MIN_SIZE       ETH_MIN_MTU
>  #define MACB_NETIF_LSO         NETIF_F_TSO
> @@ -3640,7 +3641,7 @@ static int macb_init(struct platform_device *pdev)
> 
>         /* setup appropriated routines according to adapter type */
>         if (macb_is_gem(bp)) {
> -               bp->max_tx_length = GEM_MAX_TX_LEN;
> +               bp->max_tx_length = min(GEM_MAX_TX_LEN, GEM_MAX_TX_LEN_ERRATA);

Isn't this always resolved to GEM_MAX_TX_LEN_ERRATA?

>                 bp->macbgem_ops.mog_alloc_rx_buffers = gem_alloc_rx_buffers;
>                 bp->macbgem_ops.mog_free_rx_buffers = gem_free_rx_buffers;
>                 bp->macbgem_ops.mog_init_rings = gem_init_rings;
> --
> 2.7.4
> 
>