Re: [PATCHv2] virtio_console: Add support for remoteproc serial

[Rusty Russell]

sjur.brandeland@xxxxxxxxxxxxxx writes:

> From: Sjur BrÃndeland <sjur.brandeland@xxxxxxxxxxxxxx>
>
> Add a simple serial connection driver called
> VIRTIO_ID_RPROC_SERIAL (0xB) for communicating with a
> remote processor in an asymmetric multi-processing
> configuration.
>
> This implementation reuses the existing virtio_console
> implementation, and adds support for DMA allocation
> of data buffers and disables use of tty console and
> the virtio control queue.
>
> This enables use of the exising virtio_console code in
> the remoteproc framework.

OK, I'll let Amit comment on the console changes, but some minor style
comments below:

> +#if IS_ENABLED(CONFIG_REMOTEPROC)
> +static inline bool is_rproc_serial(struct virtio_device *vdev)
> +{
> +	return vdev->id.device == VIRTIO_ID_RPROC_SERIAL;
> +}
> +#else
> +static inline bool is_rproc_serial(struct virtio_device *vdev)
> +{
> +	return false;
> +}
> +#endif

I prefer to avoid inline in C files.  The compiler knows, and with
inline you get no warning if it becomes unused.  Also, const struct
virtio_device *.

> +/* Allocate data buffer from DMA memory if requested */
> +static inline void *
> +alloc_databuf(struct virtio_device *vdev, size_t size, gfp_t flag)
> +{
> +	if (is_rproc_serial(vdev)) {
> +		dma_addr_t dma;
> +		struct device *dev = &vdev->dev;
> +		/*
> +		 * Allocate DMA memory from ancestors. Finding the ancestor
> +		 * is a bit quirky when DMA_MEMORY_INCLUDES_CHILDREN is not
> +		 * implemented.
> +		 */
> +		dev = dev->parent ? dev->parent : dev;
> +		dev = dev->parent ? dev->parent : dev;
> +		return dma_alloc_coherent(dev, size, &dma, flag);

Wow, up 2 levels?  Why 2?  What's special about the grandparents?

> -static void free_buf(struct port_buffer *buf)
> +static void
> +free_buf(struct virtqueue *vq, struct port_buffer *buf, size_t buf_size)
>  {

Generally prefer to indent buf and buf_size, rather than break at
free_buf.

> +	buf = alloc_databuf(vdev, buf_size, GFP_KERNEL);
>  
> -	buf = kmalloc(count, GFP_KERNEL);
>  	if (!buf)
>  		return -ENOMEM;

This effectively adds a blank line between "buf = ..." and "if (!buf)",
but they're adjacent because they're logically grouped.

> @@ -767,6 +826,7 @@ static int port_fops_release(struct inode *inode, struct file *filp)
>  	spin_unlock_irq(&port->inbuf_lock);
>  
>  	spin_lock_irq(&port->outvq_lock);
> +
>  	reclaim_consumed_buffers(port);
>  	spin_unlock_irq(&port->outvq_lock);
>  

Weird whitespace addition.  I know you're doing that simply to check if
I'm reading, right?

> @@ -1688,7 +1768,7 @@ static void remove_controlq_data(struct ports_device *portdev)
>   * config space to see how many ports the host has spawned.  We
>   * initialize each port found.
>   */
> -static int __devinit virtcons_probe(struct virtio_device *vdev)
> +static int virtcons_probe(struct virtio_device *vdev)
>  {
>  	struct ports_device *portdev;
>  	int err;

Not sure about this change.  If you actually turn off CONFIG_HOTPLUG,
I wouldn't think that remoteproc would work at all any more, since it
needs the driver core to match up devices?

> @@ -1724,10 +1804,12 @@ static int __devinit virtcons_probe(struct virtio_device *vdev)
>  
>  	multiport = false;
>  	portdev->config.max_nr_ports = 1;
> -	if (virtio_config_val(vdev, VIRTIO_CONSOLE_F_MULTIPORT,
> -			      offsetof(struct virtio_console_config,
> -				       max_nr_ports),
> -			      &portdev->config.max_nr_ports) == 0)
> +	if (is_rproc_serial(vdev))
> +		multiport = false;
> +	else if (virtio_config_val(vdev, VIRTIO_CONSOLE_F_MULTIPORT,
> +				  offsetof(struct virtio_console_config,
> +					   max_nr_ports),
> +				  &portdev->config.max_nr_ports) == 0)
>  		multiport = true;

This is a bit weird, to double-assign multiport = false; it looks tacked
on.

How about:

        /* Don't test MULTIPORT at all if we're rproc: not a valid feature! */
        if (!is_rproc_serial(vdev)
             && virtio_config_val(vdev, VIRTIO_CONSOLE_F_MULTIPORT,
				  offsetof(struct virtio_console_config,
					   max_nr_ports),
				  &portdev->config.max_nr_ports) == 0) {
                multiport = true;
        } else {
                multiport = false;
                portdev->config.max_nr_ports = 1;
        }

>  	err = init_vqs(portdev);
> @@ -1838,6 +1920,16 @@ static unsigned int features[] = {
>  	VIRTIO_CONSOLE_F_MULTIPORT,
>  };
>  
> +static struct virtio_device_id rproc_serial_id_table[] = {
> +#if IS_ENABLED(CONFIG_REMOTEPROC)
> +	{ VIRTIO_ID_RPROC_SERIAL, VIRTIO_DEV_ANY_ID },
> +#endif
> +	{ 0 },
> +};
> +
> +static unsigned int rproc_serial_features[] = {
> +};
> +
>  #ifdef CONFIG_PM
>  static int virtcons_freeze(struct virtio_device *vdev)
>  {
> @@ -1922,6 +2014,16 @@ static struct virtio_driver virtio_console = {
>  #endif
>  };
>  
> +static struct virtio_driver virtio_rproc_serial = {
> +	.feature_table = rproc_serial_features,
> +	.feature_table_size = ARRAY_SIZE(rproc_serial_features),
> +	.driver.name =	"virtio_rproc_serial",
> +	.driver.owner =	THIS_MODULE,
> +	.id_table =	rproc_serial_id_table,
> +	.probe =	virtcons_probe,
> +	.remove =	virtcons_remove,
> +};
> +
>  static int __init init(void)
>  {
>  	int err;
> @@ -1941,12 +2043,16 @@ static int __init init(void)
>  	INIT_LIST_HEAD(&pdrvdata.consoles);
>  	INIT_LIST_HEAD(&pdrvdata.portdevs);
>  
> -	return register_virtio_driver(&virtio_console);
> +	err = register_virtio_driver(&virtio_console);
> +	if (err)
> +		return err;
> +	return register_virtio_driver(&virtio_rproc_serial);

Hmm, we need to cleanup if the second register fails.

>  #define VIRTIO_ID_RPMSG		7 /* virtio remote processor messaging */
>  #define VIRTIO_ID_SCSI		8 /* virtio scsi */
>  #define VIRTIO_ID_9P		9 /* 9p virtio console */
> +#define VIRTIO_ID_RPROC_SERIAL	0xB /* virtio remoteproc serial link */

Prefer decimal here...

Cheers,
Rusty.
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