Re: [PATCH v8 2/2] mctp pcc: Implement MCTP over PCC Transport

[Joe Damato <jdamato@fastly.com>]

FWIW, net-next is currently closed so this would have to be resent
once it has reopened:

https://lore.kernel.org/netdev/20241118071654.695bb1a2@kernel.org/

I don't know much about MCTP, so my apologies that my review is
mostly little nits and a question/comment about stats below.

I don't think any of these are worth holding this back, but since
net-next is closed this needs to be resent, maybe worth considering?

On Wed, Nov 20, 2024 at 02:02:15PM -0500, admiyo@os.amperecomputing.com wrote:
> From: Adam Young <admiyo@os.amperecomputing.com>
> 
> 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 <admiyo@os.amperecomputing.com>
> ---
>  drivers/net/mctp/Kconfig    |  13 ++
>  drivers/net/mctp/Makefile   |   1 +
>  drivers/net/mctp/mctp-pcc.c | 321 ++++++++++++++++++++++++++++++++++++
>  3 files changed, 335 insertions(+)
>  create mode 100644 drivers/net/mctp/mctp-pcc.c

[...]

It seems like below there are a few places where unnecessary double
spaces are included. Not necessarily a reason to hold this back, but
since net-next is closed and you need to resend anyway...

> --- /dev/null
> +++ b/drivers/net/mctp/mctp-pcc.c
> @@ -0,0 +1,321 @@

[...]

> +static void mctp_pcc_client_rx_callback(struct mbox_client *c, void *buffer)
> +{
> +	struct mctp_pcc_ndev *mctp_pcc_dev;
> +	struct mctp_pcc_hdr mctp_pcc_hdr;
> +	struct mctp_skb_cb *cb;
> +	struct sk_buff *skb;
> +	void *skb_buf;
> +	u32 data_len;
> +
> +	mctp_pcc_dev = container_of(c, struct mctp_pcc_ndev, inbox.client);
> +	memcpy_fromio(&mctp_pcc_hdr, mctp_pcc_dev->inbox.chan->shmem,
> +		      sizeof(struct mctp_pcc_hdr));
> +	data_len = mctp_pcc_hdr.length + MCTP_HEADER_LENGTH;
> +
> +	if (data_len > mctp_pcc_dev->mdev.dev->mtu) {
> +		mctp_pcc_dev->mdev.dev->stats.rx_dropped++;

I'm not an expert on rtnl stats, but maybe this should be
accounted for as rx_length_errors ?

And when rx_dropped is accounted in the stats callback it can add
rx_length_errors in as well as setting rtnl_link_stats64's
rx_length_errors?

You've probably read this already, but just in case:

https://docs.kernel.org/networking/statistics.html#struct-rtnl-link-stats64

> +		return;
> +	}
> +
> +	skb = netdev_alloc_skb(mctp_pcc_dev->mdev.dev, data_len);
> +	if (!skb) {
> +		mctp_pcc_dev->mdev.dev->stats.rx_dropped++;
> +		return;
> +	}
> +	mctp_pcc_dev->mdev.dev->stats.rx_packets++;
> +	mctp_pcc_dev->mdev.dev->stats.rx_bytes += data_len;
> +	skb->protocol = htons(ETH_P_MCTP);
> +	skb_buf = skb_put(skb, data_len);
> +	memcpy_fromio(skb_buf, mctp_pcc_dev->inbox.chan->shmem, data_len);
> +
> +	skb_reset_mac_header(skb);
> +	skb_pull(skb, sizeof(struct mctp_pcc_hdr));
> +	skb_reset_network_header(skb);
> +	cb = __mctp_cb(skb);
> +	cb->halen = 0;
> +	netif_rx(skb);
> +}
> +
> +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;

Extra space after mctp_pcc_hdr ?

[...]

> +
> +static void  mctp_pcc_setup(struct net_device *ndev)

Extra space after void?

[...]

> +
> +static acpi_status lookup_pcct_indices(struct acpi_resource *ares,
> +				       void *context)
> +{
> +	struct  mctp_pcc_lookup_context *luc = context;

extra space after struct ?

[...]

> +
> +static int mctp_pcc_driver_add(struct acpi_device *acpi_dev)
> +{
> +	struct mctp_pcc_lookup_context context = {0, 0, 0};
> +	struct mctp_pcc_ndev *mctp_pcc_ndev;
> +	struct device *dev = &acpi_dev->dev;
> +	struct net_device *ndev;
> +	acpi_handle dev_handle;
> +	acpi_status status;
> +	int mctp_pcc_mtu;
> +	char name[32];
> +	int rc;
> +
> +	dev_dbg(dev, "Adding mctp_pcc device for HID %s\n",
> +		acpi_device_hid(acpi_dev));
> +	dev_handle = acpi_device_handle(acpi_dev);
> +	status = acpi_walk_resources(dev_handle, "_CRS", lookup_pcct_indices,
> +				     &context);
> +	if (!ACPI_SUCCESS(status)) {
> +		dev_err(dev, "FAILURE to lookup PCC indexes from CRS\n");
> +		return -EINVAL;
> +	}
> +
> +	//inbox initialization

I'm not sure but in net/ the general comment style seems to be /*
*/, I grepped around a bit and didn't notice many comments of this
style (except SPDX lines).

Maybe this should be a /* */ ?

> +	snprintf(name, sizeof(name), "mctpipcc%d", context.inbox_index);
> +	ndev = alloc_netdev(sizeof(struct mctp_pcc_ndev), name, NET_NAME_ENUM,
> +			    mctp_pcc_setup);
> +	if (!ndev)
> +		return -ENOMEM;
> +
> +	mctp_pcc_ndev = netdev_priv(ndev);
> +	rc =  devm_add_action_or_reset(dev, mctp_cleanup_netdev, ndev);

extra space after = ?

> +	if (rc)
> +		goto cleanup_netdev;
> +	spin_lock_init(&mctp_pcc_ndev->lock);
> +
> +	rc = mctp_pcc_initialize_mailbox(dev, &mctp_pcc_ndev->inbox,
> +					 context.inbox_index);
> +	if (rc)
> +		goto cleanup_netdev;
> +	mctp_pcc_ndev->inbox.client.rx_callback = mctp_pcc_client_rx_callback;
> +
> +	//outbox initialization

Same as above on comment style