Subject: Re: [PATCH net-next v1] net: stmmac: Programming sequence for VLAN packets with split header

From: Simon Horman <[email-masked]>
Date: Fri, 6 Sep 2024 11:28:39 +0100

On Wed, Sep 04, 2024 at 04:54:56PM -0700, Abhishek Chauhan wrote:
> Currently reset state configuration of split header works fine for
> non-tagged packets and we see no corruption in payload of any size
> 
> We need additional programming sequence with reset configuration to
> handle VLAN tagged packets to avoid corruption in payload for packets
> of size greater than 256 bytes.
> 
> Without this change ping application complains about corruption
> in payload when the size of the VLAN packet exceeds 256 bytes.
> 
> With this change tagged and non-tagged packets of any size works fine
> and there is no corruption seen.
> 
> Signed-off-by: Abhishek Chauhan <[email-masked]>

...

> diff --git a/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c b/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
> index e0165358c4ac..dbd1be4e4a92 100644
> --- a/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
> +++ b/drivers/net/ethernet/stmicro/stmmac/dwmac4_dma.c
> @@ -526,6 +526,17 @@ static void dwmac4_enable_sph(struct stmmac_priv *priv, void __iomem *ioaddr,
>  	value |= GMAC_CONFIG_HDSMS_256; /* Segment max 256 bytes */
>  	writel(value, ioaddr + GMAC_EXT_CONFIG);
>  
> +	/* Additional configuration to handle VLAN tagged packets */
> +	value = readl(ioaddr + GMAC_EXT_CFG1);
> +	value &= ~GMAC_CONFIG1_SPLM;
> +	/* Enable Split mode for header and payload at L2  */
> +	value |= GMAC_CONFIG1_SPLM_L2OFST_EN << GMAC_CONFIG1_SPLM_SHIFT;
> +	value &= ~GMAC_CONFIG1_SAVO;
> +	/* Enables the MAC to distinguish between tagged vs untagged pkts */
> +	value |= 4 << GMAC_CONFIG1_SAVO_SHIFT;
> +	value |= GMAC_CONFIG1_SAVE_EN;
> +	writel(value, ioaddr + GMAC_EXT_CFG1);

Hi Abhishek,

Perhaps it is inconsistent with the code elsewhere in this file,
in which case I would suggest a follow-up clean-up, but I
expect that using FIELD_PREP would both lead to cleaner code here
and remove the need for *_SHIFT.

> +
>  	value = readl(ioaddr + DMA_CHAN_CONTROL(dwmac4_addrs, chan));
>  	if (en)
>  		value |= DMA_CONTROL_SPH;
> -- 
> 2.25.1
> 
>