Subject: Re: [PATCH net 05/13] net: stmmac: Enable ATDS for chain-mode

From: Piotr Raczynski <[email-masked]>
Date: Tue, 14 Mar 2023 12:42:22 +0100

On Tue, Mar 14, 2023 at 01:42:29AM +0300, Serge Semin wrote:
> It wasn't stated why the Alternate Descriptor Size shouldn't have been
> changed for the chained DMA descriptors, while the original commit did
> introduce some chain_mode.c modifications. So the ATDS-related change in
> commit c24602ef8664 ("stmmac: support extend descriptors") seems
> contradicting. Anyway from the DW MAC/GMAC hardware point of view there is
> no such limitation - whether the chained descriptors can't be used
> together with the extended alternate descriptors. Moreover not setting the
> BUS_MODE.ATDS flag will cause the driver malfunction in the framework of
> the IPC Full Checksum and Advanced Timestamp feature, since the later
> features require the additional 4-7 dwords of the DMA descriptor to set
> some flags and a timestamp. So to speak in order to have all these
> features working correctly in the chained mode too let's make sure the
> ATDS flag is set irrespectively from the DMA descriptors mode.
> 
> Fixes: c24602ef8664 ("stmmac: support extend descriptors")
> Signed-off-by: Serge Semin <[email-masked]>
> ---
>  drivers/net/ethernet/stmicro/stmmac/stmmac_main.c | 7 ++-----
>  1 file changed, 2 insertions(+), 5 deletions(-)
> 
> diff --git a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> index 2ed63acaee5b..ee4297a25521 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/stmmac_main.c
> @@ -2907,7 +2907,6 @@ static int stmmac_init_dma_engine(struct stmmac_priv *priv)
>  	struct stmmac_rx_queue *rx_q;
>  	struct stmmac_tx_queue *tx_q;
>  	u32 chan = 0;
> -	int atds = 0;
>  	int ret = 0;
>  
>  	if (!priv->plat->dma_cfg || !priv->plat->dma_cfg->pbl) {
> @@ -2915,9 +2914,6 @@ static int stmmac_init_dma_engine(struct stmmac_priv *priv)
>  		return -EINVAL;
>  	}
>  
> -	if (priv->extend_desc && (priv->mode == STMMAC_RING_MODE))
> -		atds = 1;
> -
>  	ret = stmmac_reset(priv, priv->ioaddr);
>  	if (ret) {
>  		dev_err(priv->device, "Failed to reset the dma\n");
> @@ -2925,7 +2921,8 @@ static int stmmac_init_dma_engine(struct stmmac_priv *priv)
>  	}
>  
>  	/* DMA Configuration */
> -	stmmac_dma_init(priv, priv->ioaddr, priv->plat->dma_cfg, atds);
> +	stmmac_dma_init(priv, priv->ioaddr, priv->plat->dma_cfg,
> +			priv->extend_desc);
>  
>  	if (priv->plat->axi)
>  		stmmac_axi(priv, priv->ioaddr, priv->plat->axi);
> -- 
> 2.39.2
> 
> 
Looks fine, thanks.
Reviewed-by: Piotr Raczynski <[email-masked]>