virtio_console: Add support for remoteproc serial

Add a simple serial connection driver called
VIRTIO_ID_RPROC_SERIAL (11) 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.

Signed-off-by: Sjur Brændeland <sjur.brandeland@stericsson.com>
Acked-by: Amit Shah <amit.shah@redhat.com>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

1 files changed, 169 insertions, 23 deletions

diff --git a/drivers/char/virtio_console.c b/drivers/char/virtio_console.c
index 548224686963..55a89a4ae42f 100644
--- a/drivers/char/virtio_console.c
+++ b/drivers/char/virtio_console.c
@@ -37,8 +37,12 @@
 #include <linux/wait.h>
 #include <linux/workqueue.h>
 #include <linux/module.h>
+#include <linux/dma-mapping.h>
+#include <linux/kconfig.h>
 #include "../tty/hvc/hvc_console.h"
 
+#define is_rproc_enabled IS_ENABLED(CONFIG_REMOTEPROC)
+
 /*
  * This is a global struct for storing common data for all the devices
  * this driver handles.
@@ -112,6 +116,15 @@ struct port_buffer {
         /* offset in the buf from which to consume data */
         size_t offset;
 
+        /* DMA address of buffer */
+        dma_addr_t dma;
+
+        /* Device we got DMA memory from */
+        struct device *dev;
+
+        /* List of pending dma buffers to free */
+        struct list_head list;
+
         /* If sgpages == 0 then buf is used */
         unsigned int sgpages;
 
@@ -331,6 +344,11 @@ static bool is_console_port(struct port *port)
         return false;
 }
 
+static bool is_rproc_serial(const struct virtio_device *vdev)
+{
+        return is_rproc_enabled && vdev->id.device == VIRTIO_ID_RPROC_SERIAL;
+}
+
 static inline bool use_multiport(struct ports_device *portdev)
 {
         /*
@@ -342,11 +360,13 @@ 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)
+static DEFINE_SPINLOCK(dma_bufs_lock);
+static LIST_HEAD(pending_free_dma_bufs);
+
+static void free_buf(struct port_buffer *buf, bool can_sleep)
 {
         unsigned int i;
 
-        kfree(buf->buf);
         for (i = 0; i < buf->sgpages; i++) {
                 struct page *page = sg_page(&buf->sg[i]);
                 if (!page)
@@ -354,14 +374,57 @@ static void free_buf(struct port_buffer *buf)
                 put_page(page);
         }
 
+        if (!buf->dev) {
+                kfree(buf->buf);
+        } else if (is_rproc_enabled) {
+                unsigned long flags;
+
+                /* dma_free_coherent requires interrupts to be enabled. */
+                if (!can_sleep) {
+                        /* queue up dma-buffers to be freed later */
+                        spin_lock_irqsave(&dma_bufs_lock, flags);
+                        list_add_tail(&buf->list, &pending_free_dma_bufs);
+                        spin_unlock_irqrestore(&dma_bufs_lock, flags);
+                        return;
+                }
+                dma_free_coherent(buf->dev, buf->size, buf->buf, buf->dma);
+
+                /* Release device refcnt and allow it to be freed */
+                put_device(buf->dev);
+        }
+
         kfree(buf);
 }
 
+static void reclaim_dma_bufs(void)
+{
+        unsigned long flags;
+        struct port_buffer *buf, *tmp;
+        LIST_HEAD(tmp_list);
+
+        if (list_empty(&pending_free_dma_bufs))
+                return;
+
+        /* Create a copy of the pending_free_dma_bufs while holding the lock */
+        spin_lock_irqsave(&dma_bufs_lock, flags);
+        list_cut_position(&tmp_list, &pending_free_dma_bufs,
+                          pending_free_dma_bufs.prev);
+        spin_unlock_irqrestore(&dma_bufs_lock, flags);
+
+        /* Release the dma buffers, without irqs enabled */
+        list_for_each_entry_safe(buf, tmp, &tmp_list, list) {
+                list_del(&buf->list);
+                free_buf(buf, true);
+        }
+}
+
 static struct port_buffer *alloc_buf(struct virtqueue *vq, size_t buf_size,
                                      int pages)
 {
         struct port_buffer *buf;
 
+        reclaim_dma_bufs();
+
         /*
          * Allocate buffer and the sg list. The sg list array is allocated
          * directly after the port_buffer struct.
@@ -373,11 +436,34 @@ static struct port_buffer *alloc_buf(struct virtqueue *vq, size_t buf_size,
 
         buf->sgpages = pages;
         if (pages > 0) {
+                buf->dev = NULL;
                 buf->buf = NULL;
                 return buf;
         }
 
-        buf->buf = kmalloc(buf_size, GFP_KERNEL);
+        if (is_rproc_serial(vq->vdev)) {
+                /*
+                 * Allocate DMA memory from ancestor. When a virtio
+                 * device is created by remoteproc, the DMA memory is
+                 * associated with the grandparent device:
+                 * vdev => rproc => platform-dev.
+                 * The code here would have been less quirky if
+                 * DMA_MEMORY_INCLUDES_CHILDREN had been supported
+                 * in dma-coherent.c
+                 */
+                if (!vq->vdev->dev.parent || !vq->vdev->dev.parent->parent)
+                        goto free_buf;
+                buf->dev = vq->vdev->dev.parent->parent;
+
+                /* Increase device refcnt to avoid freeing it */
+                get_device(buf->dev);
+                buf->buf = dma_alloc_coherent(buf->dev, buf_size, &buf->dma,
+                                              GFP_KERNEL);
+        } else {
+                buf->dev = NULL;
+                buf->buf = kmalloc(buf_size, GFP_KERNEL);
+        }
+
         if (!buf->buf)
                 goto free_buf;
         buf->len = 0;
@@ -446,7 +532,7 @@ 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(buf, false);
                 }
                 port->inbuf = NULL;
                 buf = get_inbuf(port);
@@ -518,7 +604,7 @@ static void reclaim_consumed_buffers(struct port *port)
                 return;
         }
         while ((buf = virtqueue_get_buf(port->out_vq, &len))) {
-                free_buf(buf);
+                free_buf(buf, false);
                 port->outvq_full = false;
         }
 }
@@ -765,7 +851,7 @@ static ssize_t port_fops_write(struct file *filp, const char __user *ubuf,
                 goto out;
 
 free_buf:
-        free_buf(buf);
+        free_buf(buf, true);
 out:
         return ret;
 }
@@ -839,6 +925,15 @@ static ssize_t port_fops_splice_write(struct pipe_inode_info *pipe,
                 .u.data = &sgl,
         };
 
+        /*
+         * Rproc_serial does not yet support splice. To support splice
+         * pipe_to_sg() must allocate dma-buffers and copy content from
+         * regular pages to dma pages. And alloc_buf and free_buf must
+         * support allocating and freeing such a list of dma-buffers.
+         */
+        if (is_rproc_serial(port->out_vq->vdev))
+                return -EINVAL;
+
         ret = wait_port_writable(port, filp->f_flags & O_NONBLOCK);
         if (ret < 0)
                 return ret;
@@ -857,7 +952,7 @@ static ssize_t port_fops_splice_write(struct pipe_inode_info *pipe,
                 ret = __send_to_port(port, buf->sg, sgl.n, sgl.len, buf, true);
 
         if (unlikely(ret <= 0))
-                kfree(sgl.sg);
+                free_buf(buf, true);
         return ret;
 }
 
@@ -906,6 +1001,7 @@ static int port_fops_release(struct inode *inode, struct file *filp)
         reclaim_consumed_buffers(port);
         spin_unlock_irq(&port->outvq_lock);
 
+        reclaim_dma_bufs();
         /*
          * Locks aren't necessary here as a port can't be opened after
          * unplug, and if a port isn't unplugged, a kref would already
@@ -1057,7 +1153,10 @@ static void resize_console(struct port *port)
                 return;
 
         vdev = port->portdev->vdev;
-        if (virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE))
+
+        /* Don't test F_SIZE at all if we're rproc: not a valid feature! */
+        if (!is_rproc_serial(vdev) &&
+            virtio_has_feature(vdev, VIRTIO_CONSOLE_F_SIZE))
                 hvc_resize(port->cons.hvc, port->cons.ws);
 }
 
@@ -1249,7 +1348,7 @@ 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(buf, true);
                         break;
                 }
                 nr_added_bufs++;
@@ -1337,10 +1436,18 @@ static int add_port(struct ports_device *portdev, u32 id)
                 goto free_device;
         }
 
-        /*
-         * If we're not using multiport support, this has to be a console port
-         */
-        if (!use_multiport(port->portdev)) {
+        if (is_rproc_serial(port->portdev->vdev))
+                /*
+                 * For rproc_serial assume remote processor is connected.
+                 * rproc_serial does not want the console port, only
+                 * the generic port implementation.
+                 */
+                port->host_connected = true;
+        else if (!use_multiport(port->portdev)) {
+                /*
+                 * If we're not using multiport support,
+                 * this has to be a console port.
+                 */
                 err = init_port_console(port);
                 if (err)
                         goto free_inbufs;
@@ -1373,7 +1480,7 @@ 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(buf, true);
 free_device:
         device_destroy(pdrvdata.class, port->dev->devt);
 free_cdev:
@@ -1415,11 +1522,11 @@ 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(buf, true);
 
         /* Free pending buffers from the out-queue. */
         while ((buf = virtqueue_detach_unused_buf(port->out_vq)))
-                free_buf(buf);
+                free_buf(buf, true);
 }
 
 /*
@@ -1621,7 +1728,7 @@ 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(buf, false);
                 }
         }
         spin_unlock(&portdev->cvq_lock);
@@ -1817,10 +1924,10 @@ static void remove_controlq_data(struct ports_device *portdev)
                 return;
 
         while ((buf = virtqueue_get_buf(portdev->c_ivq, &len)))
-                free_buf(buf);
+                free_buf(buf, true);
 
         while ((buf = virtqueue_detach_unused_buf(portdev->c_ivq)))
-                free_buf(buf);
+                free_buf(buf, true);
 }
 
 /*
@@ -1867,11 +1974,15 @@ 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)
+
+        /* 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;
+        }
 
         err = init_vqs(portdev);
         if (err < 0) {
@@ -1981,6 +2092,16 @@ 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)
 {
@@ -2065,6 +2186,20 @@ static struct virtio_driver virtio_console = {
 #endif
 };
 
+/*
+ * virtio_rproc_serial refers to __devinit function which causes
+ * section mismatch warnings. So use __refdata to silence warnings.
+ */
+static struct virtio_driver __refdata 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;
@@ -2089,7 +2224,15 @@ static int __init init(void)
                 pr_err("Error %d registering virtio driver\n", err);
                 goto free;
         }
+        err = register_virtio_driver(&virtio_rproc_serial);
+        if (err < 0) {
+                pr_err("Error %d registering virtio rproc serial driver\n",
+                       err);
+                goto unregister;
+        }
         return 0;
+unregister:
+        unregister_virtio_driver(&virtio_console);
 free:
         if (pdrvdata.debugfs_dir)
                 debugfs_remove_recursive(pdrvdata.debugfs_dir);
@@ -2099,7 +2242,10 @@ free:
 
 static void __exit fini(void)
 {
+        reclaim_dma_bufs();
+
         unregister_virtio_driver(&virtio_console);
+        unregister_virtio_driver(&virtio_rproc_serial);
 
         class_destroy(pdrvdata.class);
         if (pdrvdata.debugfs_dir)