Subject: Re: [PATCH v12 1/1] mctp pcc: Implement MCTP over PCC Transport

From: Simon Horman <[email-masked]>
Date: Tue, 7 Jan 2025 11:52:27 +0000

On Mon, Jan 06, 2025 at 02:24:57PM -0500, [email-masked] wrote:
> From: Adam Young <[email-masked]>
> 
> Implementation of network driver for
> Management Control Transport Protocol(MCTP) over
> Platform Communication Channel(PCC)
> 
> DMTF DSP:0292
> https://www.dmtf.org/sites/default/files/standards/documents/DSP0292_1.0.0WIP50.pdf
> 
> MCTP devices are specified by entries in DSDT/SDST and
> reference channels specified in the PCCT.
> 
> Communication with other devices use the PCC based
> doorbell mechanism.
> 
> Signed-off-by: Adam Young <[email-masked]>

...

> +#define MCTP_PAYLOAD_LENGTH     256
> +#define MCTP_CMD_LENGTH         4
> +#define MCTP_PCC_VERSION        0x1 /* DSP0253 defines a single version: 1 */
> +#define MCTP_SIGNATURE          "MCTP"
> +#define MCTP_SIGNATURE_LENGTH   (sizeof(MCTP_SIGNATURE) - 1)
> +#define MCTP_HEADER_LENGTH      12
> +#define MCTP_MIN_MTU            68
> +#define PCC_MAGIC               0x50434300
> +#define PCC_HEADER_FLAG_REQ_INT 0x1
> +#define PCC_HEADER_FLAGS        PCC_HEADER_FLAG_REQ_INT
> +#define PCC_DWORD_TYPE          0x0c
> +
> +struct mctp_pcc_hdr {
> +	__le32 signature;
> +	__le32 flags;
> +	__le32 length;
> +	char mctp_signature[MCTP_SIGNATURE_LENGTH];
> +};
> +
> +struct mctp_pcc_mailbox {
> +	u32 index;
> +	struct pcc_mbox_chan *chan;
> +	struct mbox_client client;
> +};
> +
> +/* The netdev structure. One of these per PCC adapter. */
> +struct mctp_pcc_ndev {
> +	/* spinlock to serialize access to PCC outbox buffer and registers
> +	 * Note that what PCC calls registers are memory locations, not CPU
> +	 * Registers.  They include the fields used to synchronize access
> +	 * between the OS and remote endpoints.
> +	 *
> +	 * Only the Outbox needs a spinlock, to prevent multiple
> +	 * sent packets triggering multiple attempts to over write
> +	 * the outbox.  The Inbox buffer is controlled by the remote
> +	 * service and a spinlock would have no effect.
> +	 */
> +	spinlock_t lock;
> +	struct mctp_dev mdev;
> +	struct acpi_device *acpi_device;
> +	struct mctp_pcc_mailbox inbox;
> +	struct mctp_pcc_mailbox outbox;
> +};

...

> +static netdev_tx_t mctp_pcc_tx(struct sk_buff *skb, struct net_device *ndev)
> +{
> +	struct mctp_pcc_ndev *mpnd = netdev_priv(ndev);
> +	struct mctp_pcc_hdr  *mctp_pcc_header;
> +	void __iomem *buffer;
> +	unsigned long flags;
> +	int len = skb->len;
> +
> +	dev_dstats_tx_add(ndev, len);
> +
> +	spin_lock_irqsave(&mpnd->lock, flags);
> +	mctp_pcc_header = skb_push(skb, sizeof(struct mctp_pcc_hdr));
> +	buffer = mpnd->outbox.chan->shmem;
> +	mctp_pcc_header->signature = PCC_MAGIC | mpnd->outbox.index;

Hi Adam,

The type of mctp_pcc_header->signature is __le32.
However it is being assigned a host byte order value.
Perhaps this should be:

	mctp_pcc_header->signature = cpu_to_le32(PCC_MAGIC |
						 mpnd->outbox.index);

Flagged by Sparse.

> +	mctp_pcc_header->flags = cpu_to_le32(PCC_HEADER_FLAGS);
> +	memcpy(mctp_pcc_header->mctp_signature, MCTP_SIGNATURE,
> +	       MCTP_SIGNATURE_LENGTH);
> +	mctp_pcc_header->length = cpu_to_le32(len + MCTP_SIGNATURE_LENGTH);
> +
> +	memcpy_toio(buffer, skb->data, skb->len);
> +	mpnd->outbox.chan->mchan->mbox->ops->send_data(mpnd->outbox.chan->mchan,
> +						    NULL);
> +	spin_unlock_irqrestore(&mpnd->lock, flags);
> +
> +	dev_consume_skb_any(skb);
> +	return NETDEV_TX_OK;
> +}

...

-- 
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