linux-kernel - Re: [RFC Patch net-next v2 3/8] net: dsa: microchip: Initial hardware time stamping support

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Message-ID: <20221121231314.kabhej6ae6bl3qtj@skbuf>
Date:   Tue, 22 Nov 2022 01:13:14 +0200
From:   Vladimir Oltean <olteanv@...il.com>
To:     Arun Ramadoss <arun.ramadoss@...rochip.com>
Cc:     linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        woojung.huh@...rochip.com, UNGLinuxDriver@...rochip.com,
        andrew@...n.ch, vivien.didelot@...il.com, f.fainelli@...il.com,
        davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
        pabeni@...hat.com, linux@...linux.org.uk,
        Tristram.Ha@...rochip.com, richardcochran@...il.com
Subject: Re: [RFC Patch net-next v2 3/8] net: dsa: microchip: Initial
 hardware time stamping support

On Mon, Nov 21, 2022 at 09:11:45PM +0530, Arun Ramadoss wrote:
> +static int ksz_ptp_enable_mode(struct ksz_device *dev, bool enable)
> +{
> +	u16 data = 0;
> +
> +	/* Enable PTP mode */
> +	if (enable)
> +		data = PTP_ENABLE;
> +
> +	return ksz_rmw16(dev, REG_PTP_MSG_CONF1, PTP_ENABLE, data);
> +}
> +
> +static int ksz_set_hwtstamp_config(struct ksz_device *dev, int port,
> +				   struct hwtstamp_config *config)
> +{
> +	struct ksz_tagger_data *tagger_data = ksz_tagger_data(dev->ds);
> +	struct ksz_port *prt = &dev->ports[port];
> +	bool rx_on;
> +
> +	/* reserved for future extensions */
> +	if (config->flags)
> +		return -EINVAL;
> +
> +	switch (config->tx_type) {
> +	case HWTSTAMP_TX_OFF:
> +	case HWTSTAMP_TX_ONESTEP_P2P:
> +		prt->hwts_tx_en = config->tx_type;
> +		break;
> +	case HWTSTAMP_TX_ON:
> +		if (!is_lan937x(dev))
> +			return -ERANGE;
> +
> +		prt->hwts_tx_en = config->tx_type;
> +		break;
> +	default:
> +		return -ERANGE;
> +	}
> +
> +	switch (config->rx_filter) {
> +	case HWTSTAMP_FILTER_NONE:
> +		rx_on = false;
> +		break;
> +	default:
> +		rx_on = true;
> +		break;
> +	}
> +
> +	if (rx_on != tagger_data->hwtstamp_get_state(dev->ds)) {
> +		int ret;
> +
> +		tagger_data->hwtstamp_set_state(dev->ds, false);
> +
> +		ret = ksz_ptp_enable_mode(dev, rx_on);
> +		if (ret)
> +			return ret;
> +
> +		if (rx_on)
> +			tagger_data->hwtstamp_set_state(dev->ds, true);
> +	}

What's your excuse which such a horrible code pattern? What will happen
so bad with the packet if it's flagged with a TX timestamp request in
KSZ_SKB_CB(skb) at the same time as REG_PTP_MSG_CONF1 is written to?

Also, doesn't dev->ports[port].hwts_tx_en serve as a guard against
flagging packets for TX timestamps when you shouldn't?

> +
> +	return 0;
> +}
> diff --git a/net/dsa/tag_ksz.c b/net/dsa/tag_ksz.c
> index 37db5156f9a3..6a909a300c13 100644
> --- a/net/dsa/tag_ksz.c
> +++ b/net/dsa/tag_ksz.c
> @@ -4,6 +4,7 @@
>   * Copyright (c) 2017 Microchip Technology
>   */
>  
> +#include <linux/dsa/ksz_common.h>
>  #include <linux/etherdevice.h>
>  #include <linux/list.h>
>  #include <net/dsa.h>
> @@ -18,6 +19,62 @@
>  #define KSZ_EGRESS_TAG_LEN		1
>  #define KSZ_INGRESS_TAG_LEN		1
>  
> +#define KSZ_HWTS_EN  0
> +
> +struct ksz_tagger_private {
> +	struct ksz_tagger_data data; /* Must be first */
> +	unsigned long state;
> +};
> +
> +static struct ksz_tagger_private *
> +ksz_tagger_private(struct dsa_switch *ds)
> +{
> +	return ds->tagger_data;
> +}
> +
> +static bool ksz_hwtstamp_get_state(struct dsa_switch *ds)
> +{
> +	struct ksz_tagger_private *priv = ksz_tagger_private(ds);
> +
> +	return test_bit(KSZ_HWTS_EN, &priv->state);
> +}
> +
> +static void ksz_hwtstamp_set_state(struct dsa_switch *ds, bool on)
> +{
> +	struct ksz_tagger_private *priv = ksz_tagger_private(ds);
> +
> +	if (on)
> +		set_bit(KSZ_HWTS_EN, &priv->state);
> +	else
> +		clear_bit(KSZ_HWTS_EN, &priv->state);
> +}