Re: [RFC 1/2] virtio_console: Add support for DMA memory allocation

["Michael S. Tsirkin" <mst@redhat.com>]

On Mon, Sep 03, 2012 at 03:51:16PM +0200, sjur.brandeland@stericsson.com wrote:
> From: Sjur Brændeland <sjur.brandeland@stericsson.com>
> 
> Add feature VIRTIO_CONSOLE_F_DMA_MEM. If the architecture has
> DMA support and this feature bit is set, the virtio data buffers
> will be allocated from DMA memory.
> 
> This is needed for using virtio_console from the remoteproc
> framework.
> 
> Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
> cc: Rusty Russell <rusty@rustcorp.com.au>
> cc: Michael S. Tsirkin <mst@redhat.com>
> cc: Ohad Ben-Cohen <ohad@wizery.com>
> cc: Linus Walleij <linus.walleij@linaro.org>
> cc: virtualization@lists.linux-foundation.org

How does access to descriptors work in this setup?

> ---
>  drivers/char/virtio_console.c  |   76 ++++++++++++++++++++++++++++++++--------
>  include/linux/virtio_console.h |    1 +
>  2 files changed, 62 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
> index cdf2f54..6bfbd09 100644
> --- a/drivers/char/virtio_console.c
> +++ b/drivers/char/virtio_console.c
> @@ -35,6 +35,7 @@
>  #include <linux/wait.h>
>  #include <linux/workqueue.h>
>  #include <linux/module.h>
> +#include <linux/dma-mapping.h>
>  #include "../tty/hvc/hvc_console.h"
>  
>  /*
> @@ -334,20 +335,60 @@ static inline bool use_multiport(struct ports_device *portdev)
>  	return portdev->vdev->features[0] & (1 << VIRTIO_CONSOLE_F_MULTIPORT);
>  }
>  
> -static void free_buf(struct port_buffer *buf)
> +/* Allcoate data buffer from DMA memory if requested */

typo

> +static inline void *
> +alloc_databuf(struct virtio_device *vdev, size_t size, dma_addr_t *dma_handle,
> +		   gfp_t flag)
>  {
> -	kfree(buf->buf);
> +#ifdef CONFIG_HAS_DMA
> +	if (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_DMA_MEM)) {
> +		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_handle, flag);
> +	}
> +#endif

Are these ifdefs really needed? If DMA_MEM is set,
can't we use dma_alloc_coherent
unconditionally?

> +	return kzalloc(size, flag);
> +}
> +
> +static inline void
> +free_databuf(struct virtio_device *vdev, size_t size, void *cpu_addr)
> +{
> +#ifdef CONFIG_HAS_DMA
> +	dma_addr_t dma_handle = virt_to_bus(cpu_addr);
> +	if (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_DMA_MEM)) {
> +		struct device *dev = &vdev->dev;
> +
> +		dev = dev->parent ? dev->parent : dev;
> +		dev = dev->parent ? dev->parent : dev;
> +		dma_free_coherent(dev, size, cpu_addr, dma_handle);
> +		return;
> +	}
> +#endif
> +	kfree(cpu_addr);
> +}
> +
> +static void
> +free_buf(struct virtqueue *vq, struct port_buffer *buf, size_t buf_size)
> +{
> +	free_databuf(vq->vdev, buf_size, buf);
>  	kfree(buf);
>  }
>  
> -static struct port_buffer *alloc_buf(size_t buf_size)
> +static struct port_buffer *alloc_buf(struct virtqueue *vq, size_t buf_size)
>  {
>  	struct port_buffer *buf;
> +	dma_addr_t dma;
>  
>  	buf = kmalloc(sizeof(*buf), GFP_KERNEL);
>  	if (!buf)
>  		goto fail;
> -	buf->buf = kzalloc(buf_size, GFP_KERNEL);
> +	buf->buf = alloc_databuf(vq->vdev, buf_size, &dma, GFP_KERNEL);
>  	if (!buf->buf)
>  		goto free_buf;
>  	buf->len = 0;
> @@ -414,7 +455,7 @@ static void discard_port_data(struct port *port)
>  		port->stats.bytes_discarded += buf->len - buf->offset;
>  		if (add_inbuf(port->in_vq, buf) < 0) {
>  			err++;
> -			free_buf(buf);
> +			free_buf(port->in_vq, buf, PAGE_SIZE);
>  		}
>  		port->inbuf = NULL;
>  		buf = get_inbuf(port);
> @@ -485,7 +526,7 @@ static void reclaim_consumed_buffers(struct port *port)
>  		return;
>  	}
>  	while ((buf = virtqueue_get_buf(port->out_vq, &len))) {
> -		kfree(buf);
> +		free_databuf(port->portdev->vdev, len, buf);
>  		port->outvq_full = false;
>  	}
>  }
> @@ -672,6 +713,8 @@ static ssize_t port_fops_write(struct file *filp, const char __user *ubuf,
>  	char *buf;
>  	ssize_t ret;
>  	bool nonblock;
> +	struct virtio_device *vdev;
> +	dma_addr_t dma;
>  
>  	/* Userspace could be out to fool us */
>  	if (!count)
> @@ -694,9 +737,10 @@ static ssize_t port_fops_write(struct file *filp, const char __user *ubuf,
>  	if (!port->guest_connected)
>  		return -ENODEV;
>  
> +	vdev = port->portdev->vdev;
>  	count = min((size_t)(32 * 1024), count);
>  
> -	buf = kmalloc(count, GFP_KERNEL);
> +	buf = alloc_databuf(vdev, count, &dma, GFP_KERNEL);
>  	if (!buf)
>  		return -ENOMEM;
>  
> @@ -720,7 +764,8 @@ static ssize_t port_fops_write(struct file *filp, const char __user *ubuf,
>  		goto out;
>  
>  free_buf:
> -	kfree(buf);
> +	free_databuf(vdev, count, buf);
> +
>  out:
>  	return ret;
>  }
> @@ -1102,7 +1147,7 @@ static unsigned int fill_queue(struct virtqueue *vq, spinlock_t *lock)
>  
>  	nr_added_bufs = 0;
>  	do {
> -		buf = alloc_buf(PAGE_SIZE);
> +		buf = alloc_buf(vq, PAGE_SIZE);
>  		if (!buf)
>  			break;
>  
> @@ -1110,7 +1155,7 @@ static unsigned int fill_queue(struct virtqueue *vq, spinlock_t *lock)
>  		ret = add_inbuf(vq, buf);
>  		if (ret < 0) {
>  			spin_unlock_irq(lock);
> -			free_buf(buf);
> +			free_buf(vq, buf, PAGE_SIZE);
>  			break;
>  		}
>  		nr_added_bufs++;
> @@ -1234,7 +1279,7 @@ static int add_port(struct ports_device *portdev, u32 id)
>  
>  free_inbufs:
>  	while ((buf = virtqueue_detach_unused_buf(port->in_vq)))
> -		free_buf(buf);
> +		free_buf(port->in_vq, buf, PAGE_SIZE);
>  free_device:
>  	device_destroy(pdrvdata.class, port->dev->devt);
>  free_cdev:
> @@ -1276,7 +1321,7 @@ static void remove_port_data(struct port *port)
>  
>  	/* Remove buffers we queued up for the Host to send us data in. */
>  	while ((buf = virtqueue_detach_unused_buf(port->in_vq)))
> -		free_buf(buf);
> +		free_buf(port->in_vq, buf, PAGE_SIZE);
>  }
>  
>  /*
> @@ -1478,7 +1523,7 @@ static void control_work_handler(struct work_struct *work)
>  		if (add_inbuf(portdev->c_ivq, buf) < 0) {
>  			dev_warn(&portdev->vdev->dev,
>  				 "Error adding buffer to queue\n");
> -			free_buf(buf);
> +			free_buf(portdev->c_ivq, buf, PAGE_SIZE);
>  		}
>  	}
>  	spin_unlock(&portdev->cvq_lock);
> @@ -1674,10 +1719,10 @@ static void remove_controlq_data(struct ports_device *portdev)
>  		return;
>  
>  	while ((buf = virtqueue_get_buf(portdev->c_ivq, &len)))
> -		free_buf(buf);
> +		free_buf(portdev->c_ivq, buf, PAGE_SIZE);
>  
>  	while ((buf = virtqueue_detach_unused_buf(portdev->c_ivq)))
> -		free_buf(buf);
> +		free_buf(portdev->c_ivq, buf, PAGE_SIZE);
>  }
>  
>  /*
> @@ -1836,6 +1881,7 @@ static struct virtio_device_id id_table[] = {
>  static unsigned int features[] = {
>  	VIRTIO_CONSOLE_F_SIZE,
>  	VIRTIO_CONSOLE_F_MULTIPORT,
> +	VIRTIO_CONSOLE_F_DMA_MEM,
>  };
>  
>  #ifdef CONFIG_PM
> diff --git a/include/linux/virtio_console.h b/include/linux/virtio_console.h
> index bdf4b00..b27f7fa 100644
> --- a/include/linux/virtio_console.h
> +++ b/include/linux/virtio_console.h
> @@ -38,6 +38,7 @@
>  /* Feature bits */
>  #define VIRTIO_CONSOLE_F_SIZE	0	/* Does host provide console size? */
>  #define VIRTIO_CONSOLE_F_MULTIPORT 1	/* Does host provide multiple ports? */
> +#define VIRTIO_CONSOLE_F_DMA_MEM 2	/* Use DMA memory in vrings */
>  
>  #define VIRTIO_CONSOLE_BAD_ID		(~(u32)0)
>  
> -- 
> 1.7.5.4