netdev - Re: [PATCH net-next v1 2/2] net: dsa: microchip: add ETS Qdisc support for KSZ9477 series

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Date:   Wed, 8 Mar 2023 08:16:49 +0100
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     "David S. Miller" <davem@...emloft.net>,
        Andrew Lunn <andrew@...n.ch>,
        Eric Dumazet <edumazet@...gle.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Vladimir Oltean <olteanv@...il.com>,
        Woojung Huh <woojung.huh@...rochip.com>
Cc:     kernel@...gutronix.de, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org, UNGLinuxDriver@...rochip.com
Subject: Re: [PATCH net-next v1 2/2] net: dsa: microchip: add ETS Qdisc
 support for KSZ9477 series

On Mon, Mar 06, 2023 at 01:49:40PM +0100, Oleksij Rempel wrote:
> +static int ksz_queue_set_strict(struct ksz_device *dev, int port, int queue)
> +{
> +	int ret;
> +
> +	/* In order to ensure proper prioritization, it is necessary to set the
> +	 * rate limit for the related queue to zero. Otherwise strict priority
> +	 * mode will not work.
> +	 */
> +	ret = ksz_pwrite8(dev, port, KSZ9477_REG_PORT_OUT_RATE_0 + queue,
> +			  KSZ9477_OUT_RATE_NO_LIMIT);

Uff, this part works by accident. KSZ9477_REG_PORT_OUT_RATE_0 registers
should be written in a direct order. According to the documentation
"update will not take effect until the Port Queue 3 Egress Limit
Control Register is written.". But we are writing in a reverse order -
queue 3 is written first.

> +	if (ret)
> +		return ret;
> +
> +	ret = ksz_pwrite32(dev, port, REG_PORT_MTI_QUEUE_INDEX__4, queue);
> +	if (ret)
> +		return ret;
> +
> +	return ksz_setup_tc_mode(dev, port, MTI_SCHEDULE_STRICT_PRIO,
> +				 MTI_SHAPING_OFF);
> +}
> +
> +static int ksz_queue_set_wrr(struct ksz_device *dev, int port, int queue,
> +			     int weight)
> +{
> +	int ret;
> +
> +	/* In order to ensure proper prioritization, it is necessary to set the
> +	 * rate limit for the related queue to zero. Otherwise weighted round
> +	 * robin mode will not work.
> +	 */
> +	ret = ksz_pwrite8(dev, port, KSZ9477_REG_PORT_OUT_RATE_0 + queue,
> +			  KSZ9477_OUT_RATE_NO_LIMIT);

same here.
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