linux-kernel - Re: [PATCH net-next 2/2] net: ethernet: ti: am65-cpsw: enable DSCP to priority map for RX

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Message-ID: <8e6053ca-77fc-4f03-ae54-3f6af0addb88@ti.com>
Date: Fri, 8 Nov 2024 18:00:28 +0530
From: Siddharth Vadapalli <s-vadapalli@...com>
To: Roger Quadros <rogerq@...nel.org>
CC: Siddharth Vadapalli <s-vadapalli@...com>,
        Andrew Lunn
	<andrew+netdev@...n.ch>,
        "David S. Miller" <davem@...emloft.net>,
        Eric
 Dumazet <edumazet@...gle.com>, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni
	<pabeni@...hat.com>, Simon Horman <horms@...nel.org>,
        <linux-omap@...r.kernel.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>, <srk@...com>,
        Pekka Varis <p-varis@...com>
Subject: Re: [PATCH net-next 2/2] net: ethernet: ti: am65-cpsw: enable DSCP
 to priority map for RX

On Tue, Nov 05, 2024 at 04:18:11PM +0200, Roger Quadros wrote:

Hello Roger,

> AM65 CPSW hardware can map the 6-bit DSCP/TOS field to
> appropriate priority queue via DSCP to Priority mapping registers
> (CPSW_PN_RX_PRI_MAP_REG).
> 
> We use the upper 3 bits of the DSCP field that indicate IP Precedence
> to map traffic to 8 priority queues.
> 
> Signed-off-by: Roger Quadros <rogerq@...nel.org>
> ---
>  drivers/net/ethernet/ti/am65-cpsw-nuss.c | 50 ++++++++++++++++++++++++++++++++
>  1 file changed, 50 insertions(+)
> 
> diff --git a/drivers/net/ethernet/ti/am65-cpsw-nuss.c b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> index 0520e9f4bea7..65fbf6727e02 100644
> --- a/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> +++ b/drivers/net/ethernet/ti/am65-cpsw-nuss.c
> @@ -71,6 +71,8 @@
>  #define AM65_CPSW_PORT_REG_RX_PRI_MAP		0x020
>  #define AM65_CPSW_PORT_REG_RX_MAXLEN		0x024
>  
> +#define AM65_CPSW_PORTN_REG_CTL			0x004

nitpick: indentation needs to be fixed here to align with the macros
below.

> +#define AM65_CPSW_PORTN_REG_DSCP_MAP		0x120
>  #define AM65_CPSW_PORTN_REG_SA_L		0x308
>  #define AM65_CPSW_PORTN_REG_SA_H		0x30c
>  #define AM65_CPSW_PORTN_REG_TS_CTL              0x310
> @@ -94,6 +96,10 @@
>  /* AM65_CPSW_PORT_REG_PRI_CTL */
>  #define AM65_CPSW_PORT_REG_PRI_CTL_RX_PTYPE_RROBIN	BIT(8)
>  
> +/* AM65_CPSW_PN_REG_CTL */
> +#define AM65_CPSW_PN_REG_CTL_DSCP_IPV4_EN	BIT(1)
> +#define AM65_CPSW_PN_REG_CTL_DSCP_IPV6_EN	BIT(2)
> +
>  /* AM65_CPSW_PN_TS_CTL register fields */
>  #define AM65_CPSW_PN_TS_CTL_TX_ANX_F_EN		BIT(4)
>  #define AM65_CPSW_PN_TS_CTL_TX_VLAN_LT1_EN	BIT(5)
> @@ -176,6 +182,49 @@ static void am65_cpsw_port_set_sl_mac(struct am65_cpsw_port *slave,
>  	writel(mac_lo, slave->port_base + AM65_CPSW_PORTN_REG_SA_L);
>  }
>  
> +#define AM65_CPSW_DSCP_MAX	GENMASK(5, 0)
> +#define AM65_CPSW_PRI_MAX	GENMASK(2, 0)
> +static int am65_cpsw_port_set_dscp_map(struct am65_cpsw_port *slave, u8 dscp, u8 pri)
> +{
> +	int reg_ofs;
> +	int bit_ofs;
> +	u32 val;
> +
> +	if (dscp > AM65_CPSW_DSCP_MAX)
> +		return -EINVAL;

am65_cpsw_port_set_dscp_map() seems to be invoked by
am65_cpsw_port_enable_dscp_map() below, where the above check is guaranteed
to be satisfied. Is the check added for future-proofing this function?

> +
> +	if (pri > AM65_CPSW_PRI_MAX)
> +		return -EINVAL;
> +
> +	reg_ofs = (dscp / 8) * 4;	/* reg offset to this dscp */
> +	bit_ofs = 4 * (dscp % 8);	/* bit offset to this dscp */

Maybe a macro can be used for the "4" since it is not clear what it
corresponds to. Or maybe two macros can be used for "reg_ofs" and
"bit_ofs".

> +	val = readl(slave->port_base + AM65_CPSW_PORTN_REG_DSCP_MAP + reg_ofs);
> +	val &= ~(AM65_CPSW_PRI_MAX << bit_ofs);	/* clear */
> +	val |= pri << bit_ofs;			/* set */
> +	writel(val, slave->port_base + AM65_CPSW_PORTN_REG_DSCP_MAP + reg_ofs);
> +	val = readl(slave->port_base + AM65_CPSW_PORTN_REG_DSCP_MAP + reg_ofs);

The above readback seems to be just to flush the writel(). A comment of
the form:
/* flush */
might help, considering that other drivers do the same. Also, assigning
the returned value to "val" might not be required unless it is intended to
be checked.

[...]

Regards,
Siddharth.