linux-kernel - Re: [RFC PATCH v2 3/3] PCI: endpoint: Add EP function driver to provide virtio-console functionality

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Date:   Thu, 27 Apr 2023 13:09:06 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Shunsuke Mie <mie@...l.co.jp>
Cc:     Lorenzo Pieralisi <lpieralisi@...nel.org>,
        Krzysztof Wilczyński <kw@...ux.com>,
        Manivannan Sadhasivam <mani@...nel.org>,
        Kishon Vijay Abraham I <kishon@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        "Michael S. Tsirkin" <mst@...hat.com>,
        Jason Wang <jasowang@...hat.com>, Frank Li <Frank.Li@....com>,
        Jon Mason <jdmason@...zu.us>,
        Randy Dunlap <rdunlap@...radead.org>,
        Ren Zhijie <renzhijie2@...wei.com>,
        linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
        virtualization@...ts.linux-foundation.org
Subject: Re: [RFC PATCH v2 3/3] PCI: endpoint: Add EP function driver to
 provide virtio-console functionality

Random typos and trivial things.  No need to repost until somebody
does a more substantive review.

On Thu, Apr 27, 2023 at 07:44:28PM +0900, Shunsuke Mie wrote:
> Add a new PCIe endpoint function driver that works as a pci virtio-console
> device. The console connect to endpoint side console. It enables to
> communicate PCIe host and endpoint.

s/pci/PCI/

> Architecture is following:
> 
>  ┌────────────┐         ┌──────────────────────┬────────────┐
>  │virtioe     │         │                      │virtio      │
>  │console drv │         ├───────────────┐      │console drv │
>  ├────────────┤         │(virtio console│      ├────────────┤
>  │ virtio bus │         │ device)       │◄────►│ virtio bus │
>  ├────────────┤         ├---------------┤      └────────────┤
>  │            │         │ pci ep virtio │                   │
>  │  pci bus   │         │  console drv  │                   │
>  │            │  pcie   ├───────────────┤                   │
>  │            │ ◄─────► │  pci ep Bus   │                   │
>  └────────────┘         └───────────────┴───────────────────┘
>    PCIe Root              PCIe Endpoint

s/virtioe/virtio/
s/pci/PCI/
s/pcie/PCIe/
s/ep/EP/

> +config PCI_EPF_VCON
> +	tristate "PCI Endpoint virito-console driver"

s/virito/virtio/

> +	depends on PCI_ENDPOINT
> +	select VHOST_RING
> +	select PCI_EPF_VIRTIO
> +	help
> +	  PCIe Endpoint virtio-console function implementatino. This module
> +	  enables to show the virtio-console as pci device to PCIe host side, and
> +	  another virtual virtio-console device registers to endpoint system.
> +	  Those devices are connected virtually and can communicate each other.

s/implementatino/implementation/
s/pci/PCI/
s/can communicate/can communicate with/

> + * PCI Endpoint function driver to impliment virtio-console device
> + * functionality.

s/impliment/implement/

> +static int virtio_queue_size = 0x100;
> +module_param(virtio_queue_size, int, 0444);
> +MODULE_PARM_DESC(virtio_queue_size, "A length of virtqueue");

When and why would users need this parameter?  Where is it documented?

> +	/* To access virtqueus of local host driver */

s/virtqueus/virtqueues/

> +	/* To show a status whether this driver is ready and the remote is connected */

Make this fit in 80 columns.

> +	/* This is a minimum implementation. Doesn't support any features of
> +	 * virtio console. It means driver and device use just 2 virtuque for tx
> +	 * and rx.
> +	 */

Use common multi-line comment style:

  /*
   * This is ...
   */

s/virtuque/virtqueues/

> +static void epf_vcon_raise_irq_handler(struct work_struct *work)
> +{
> +	struct epf_vcon *vcon =
> +		container_of(work, struct epf_vcon, raise_irq_work);

Rewrap.

> +static int epf_vcon_setup_common(struct epf_vcon *vcon)
> +{
> +	vcon->features = 0;
> +	vcon->connected = false;
> +
> +	vcon->task_wq =
> +		alloc_workqueue("pci-epf-vcon/task-wq",

Looks like this would fit on the previous line?

> +				WQ_MEM_RECLAIM | WQ_HIGHPRI | WQ_UNBOUND, 0);

> +static void epf_vcon_initialize_complete(void *param)
> +{
> +	struct epf_vcon *vcon = param;
> +
> +	pr_debug("Remote host has connected\n");

Is there any device info you could include here, e.g., with dev_dbg()?
It's nice if users have a little context.

> +static int epf_vcon_setup_ep_func(struct epf_vcon *vcon, struct pci_epf *epf)
> +{
> +	int err;
> +	struct epf_virtio *evio = &vcon->evio;
> +	unsigned int nvq = epf_vcon_get_nvq(vcon);
> +
> +	vcon->rdev_iovs =
> +		kmalloc_array(nvq, sizeof(vcon->rdev_iovs[0]), GFP_KERNEL);

Move the function name and as many parameters as fit in 80 columns to
the previous line to match prevailing style.

> +	/* There is no config for virtio console because this console device
> +	 * doesn't any support features
> +	 */

Multi-line comment style.

s/doesn't any support/doesn't support any/?  Is that what you mean?

> +	/* Do nothing because this console device doesn't any support features */

Same.

> +static void epf_vcon_vdev_set_status(struct virtio_device *vdev, u8 status)
> +{
> +	if (status & VIRTIO_CONFIG_S_FAILED)
> +		pr_debug("driver failed to setup this device\n");

dev_dbg() if possible.

> +		err = vringh_init_kern(&vcon->vdev_vrhs[i], vcon->features,
> +				       virtio_queue_size, false, vring->desc,
> +				       vring->avail, vring->used);
> +		if (err) {
> +			pr_err("failed to init vringh for vring %d\n", i);

dev_err() if possible.

> +static int epf_vcon_setup_vdev(struct epf_vcon *vcon, struct device *parent)
> +{
> +	int err;
> +	struct virtio_device *vdev = &vcon->vdev;
> +	const unsigned int nvq = epf_vcon_get_nvq(vcon);
> +
> +	vcon->vdev_vrhs =
> +		kmalloc_array(nvq, sizeof(vcon->vdev_vrhs[0]), GFP_KERNEL);

Rewrap.

> +	vcon->vdev_iovs =
> +		kmalloc_array(nvq, sizeof(vcon->vdev_iovs[0]), GFP_KERNEL);

Rewrap.

> +	vcon->vdev_vqs =
> +		kmalloc_array(nvq, sizeof(vcon->vdev_vrhs[0]), GFP_KERNEL);

Rewrap.

> +static void epf_vcon_cleanup_vdev(struct epf_vcon *vcon)
> +{
> +	unregister_virtio_device(&vcon->vdev);
> +	/* Cleanup struct virtio_device that has kobject, otherwise error occures when
> +	 * reregister the virtio device.
> +	 */

Multi-line style and rewrap to fit in 80 columns.

> +static int __init epf_vcon_init(void)
> +{
> +	int err;
> +
> +	err = pci_epf_register_driver(&epf_vcon_drv);
> +	if (err)
> +		pr_err("Failed to register PCI EP virtio-console function\n");

dev_err() if possible (doesn't look like it *is* possible).

Looks like this registers a *driver*, so maybe change the message from
"function" to "driver"?

Bjorn