linux-kernel - Re: [net-next RFC PATCH v4 12/15] net: dsa: qca8k: add support for mdio read/write in Ethernet packet

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Date:   Sat, 11 Dec 2021 20:12:51 -0800
From:   Florian Fainelli <f.fainelli@...il.com>
To:     Ansuel Smith <ansuelsmth@...il.com>, Andrew Lunn <andrew@...n.ch>,
        Vivien Didelot <vivien.didelot@...il.com>,
        Vladimir Oltean <olteanv@...il.com>,
        "David S. Miller" <davem@...emloft.net>,
        Jakub Kicinski <kuba@...nel.org>, linux-kernel@...r.kernel.org,
        netdev@...r.kernel.org
Subject: Re: [net-next RFC PATCH v4 12/15] net: dsa: qca8k: add support for
 mdio read/write in Ethernet packet



On 12/11/2021 11:57 AM, Ansuel Smith wrote:
> Add qca8k side support for mdio read/write in Ethernet packet.
> qca8k supports some specially crafted Ethernet packet that can be used
> for mdio read/write instead of the legacy method uart/internal mdio.
> This add support for the qca8k side to craft the packet and enqueue it.
> Each port and the qca8k_priv have a special struct to put data in it.
> The completion API is used to wait for the packet to be received back
> with the requested data.
> 
> The various steps are:
> 1. Craft the special packet with the qca hdr set to mdio read/write
>     mode.
> 2. Set the lock in the dedicated mdio struct.
> 3. Reinit the completion.
> 4. Enqueue the packet.
> 5. Wait the packet to be received.
> 6. Use the data set by the tagger to complete the mdio operation.
> 
> If the completion timeouts or the ack value is not true, the legacy
> mdio way is used.
> 
> It has to be considered that in the initial setup mdio is still used and
> mdio is still used until DSA is ready to accept and tag packet.
> 
> tag_proto_connect() is used to fill the required handler for the tagger
> to correctly parse and elaborate the special Ethernet mdio packet.
> 
> Signed-off-by: Ansuel Smith <ansuelsmth@...il.com>
> ---

[snip]

> +
> +static struct sk_buff *qca8k_alloc_mdio_header(enum mdio_cmd cmd, u32 reg, u32 *val,
> +					       int seq_num)
> +{
> +	struct mdio_ethhdr *mdio_ethhdr;
> +	struct sk_buff *skb;
> +	u16 hdr;
> +
> +	skb = dev_alloc_skb(QCA_HDR_MDIO_PKG_LEN);

No out of memory condition handling?

> +
> +	prefetchw(skb->data);

What's the point you are going to dirty the cache lines right below with 
your skb_push().

> +
> +	skb_reset_mac_header(skb);
> +	skb_set_network_header(skb, skb->len);
> +
> +	mdio_ethhdr = skb_push(skb, QCA_HDR_MDIO_HEADER_LEN + QCA_HDR_LEN);
> +
> +	hdr = FIELD_PREP(QCA_HDR_XMIT_VERSION, QCA_HDR_VERSION);
> +	hdr |= QCA_HDR_XMIT_FROM_CPU;
> +	hdr |= FIELD_PREP(QCA_HDR_XMIT_DP_BIT, BIT(0));
> +	hdr |= FIELD_PREP(QCA_HDR_XMIT_CONTROL, QCA_HDR_XMIT_TYPE_RW_REG);
> +
> +	mdio_ethhdr->seq = FIELD_PREP(QCA_HDR_MDIO_SEQ_NUM, seq_num);
> +
> +	mdio_ethhdr->command = FIELD_PREP(QCA_HDR_MDIO_ADDR, reg);
> +	mdio_ethhdr->command |= FIELD_PREP(QCA_HDR_MDIO_LENGTH, 4);
> +	mdio_ethhdr->command |= FIELD_PREP(QCA_HDR_MDIO_CMD, cmd);
> +	mdio_ethhdr->command |= FIELD_PREP(QCA_HDR_MDIO_CHECK_CODE, MDIO_CHECK_CODE_VAL);
> +
> +	if (cmd == MDIO_WRITE)
> +		mdio_ethhdr->mdio_data = *val;
> +
> +	mdio_ethhdr->hdr = htons(hdr);
> +
> +	skb_put_zero(skb, QCA_HDR_MDIO_DATA2_LEN);
> +	skb_put_zero(skb, QCA_HDR_MDIO_PADDING_LEN);
> +
> +	return skb;
> +}
> +
> +static int qca8k_read_eth(struct qca8k_priv *priv, u32 reg, u32 *val)
> +{
> +	struct qca8k_mdio_hdr_data *mdio_hdr_data = &priv->mdio_hdr_data;
> +	struct sk_buff *skb;
> +	bool ack;
> +	int ret;
> +
> +	skb = qca8k_alloc_mdio_header(MDIO_READ, reg, NULL, 200);
> +	skb->dev = dsa_to_port(priv->ds, 0)->master;

Surely you should be checking that this is the CPU port and obtain it 
from DSA instead of hard coding it to 0.

> +
> +	mutex_lock(&mdio_hdr_data->mutex);
> +
> +	reinit_completion(&mdio_hdr_data->rw_done);
> +	mdio_hdr_data->seq = 200;
> +	mdio_hdr_data->ack = false;
> +
> +	dev_queue_xmit(skb);
> +
> +	ret = wait_for_completion_timeout(&mdio_hdr_data->rw_done, QCA8K_ETHERNET_TIMEOUT);

msec_to_jiffies(QCA8K_ETHERNET_TIMEOUT) at least?
-- 
Florian