drivers/char/virtio_console.c

   1 /*D:300
   2  * The Guest console driver
   3  *
   4  * Writing console drivers is one of the few remaining Dark Arts in Linux.
   5  * Fortunately for us, the path of virtual consoles has been well-trodden by
   6  * the PowerPC folks, who wrote "hvc_console.c" to generically support any
   7  * virtual console.  We use that infrastructure which only requires us to write
   8  * the basic put_chars and get_chars functions and call the right register
   9  * functions.
  10  :*/
  11
  12 /*M:002 The console can be flooded: while the Guest is processing input the
  13  * Host can send more.  Buffering in the Host could alleviate this, but it is a
  14  * difficult problem in general. :*/
  15 /* Copyright (C) 2006, 2007 Rusty Russell, IBM Corporation
  16  *
  17  * This program is free software; you can redistribute it and/or modify
  18  * it under the terms of the GNU General Public License as published by
  19  * the Free Software Foundation; either version 2 of the License, or
  20  * (at your option) any later version.
  21  *
  22  * This program is distributed in the hope that it will be useful,
  23  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  24  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  25  * GNU General Public License for more details.
  26  *
  27  * You should have received a copy of the GNU General Public License
  28  * along with this program; if not, write to the Free Software
  29  * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  30  */
  31 #include <linux/err.h>
  32 #include <linux/init.h>
  33 #include <linux/virtio.h>
  34 #include <linux/virtio_console.h>
  35 #include "hvc_console.h"
  36
  37 /*D:340 These represent our input and output console queues, and the virtio
  38  * operations for them. */
  39 static struct virtqueue *in_vq, *out_vq;
  40 static struct virtio_device *vdev;
  41
  42 /* This is our input buffer, and how much data is left in it. */
  43 static unsigned int in_len;
  44 static char *in, *inbuf;
  45
  46 /* The operations for our console. */
  47 static struct hv_ops virtio_cons;
  48
  49 /* The hvc device */
  50 static struct hvc_struct *hvc;
  51
  52 /*D:310 The put_chars() callback is pretty straightforward.
  53  *
  54  * We turn the characters into a scatter-gather list, add it to the output
  55  * queue and then kick the Host.  Then we sit here waiting for it to finish:
  56  * inefficient in theory, but in practice implementations will do it
  57  * immediately (lguest's Launcher does). */
  58 static int put_chars(u32 vtermno, const char *buf, int count)
  59 {
  60         struct scatterlist sg[1];
  61         unsigned int len;
  62
  63         /* This is a convenient routine to initialize a single-elem sg list */
  64         sg_init_one(sg, buf, count);
  65
  66         /* add_buf wants a token to identify this buffer: we hand it any
  67          * non-NULL pointer, since there's only ever one buffer. */
  68         if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) == 0) {
  69                 /* Tell Host to go! */
  70                 out_vq->vq_ops->kick(out_vq);
  71                 /* Chill out until it's done with the buffer. */
  72                 while (!out_vq->vq_ops->get_buf(out_vq, &len))
  73                         cpu_relax();
  74         }
  75
  76         /* We're expected to return the amount of data we wrote: all of it. */
  77         return count;
  78 }
  79
  80 /* Create a scatter-gather list representing our input buffer and put it in the
  81  * queue. */
  82 static void add_inbuf(void)
  83 {
  84         struct scatterlist sg[1];
  85         sg_init_one(sg, inbuf, PAGE_SIZE);
  86
  87         /* We should always be able to add one buffer to an empty queue. */
  88         if (in_vq->vq_ops->add_buf(in_vq, sg, 0, 1, inbuf) != 0)
  89                 BUG();
  90         in_vq->vq_ops->kick(in_vq);
  91 }
  92
  93 /*D:350 get_chars() is the callback from the hvc_console infrastructure when
  94  * an interrupt is received.
  95  *
  96  * Most of the code deals with the fact that the hvc_console() infrastructure
  97  * only asks us for 16 bytes at a time.  We keep in_offset and in_used fields
  98  * for partially-filled buffers. */
  99 static int get_chars(u32 vtermno, char *buf, int count)
 100 {
 101         /* If we don't have an input queue yet, we can't get input. */
 102         BUG_ON(!in_vq);
 103
 104         /* No buffer?  Try to get one. */
 105         if (!in_len) {
 106                 in = in_vq->vq_ops->get_buf(in_vq, &in_len);
 107                 if (!in)
 108                         return 0;
 109         }
 110
 111         /* You want more than we have to give?  Well, try wanting less! */
 112         if (in_len < count)
 113                 count = in_len;
 114
 115         /* Copy across to their buffer and increment offset. */
 116         memcpy(buf, in, count);
 117         in += count;
 118         in_len -= count;
 119
 120         /* Finished?  Re-register buffer so Host will use it again. */
 121         if (in_len == 0)
 122                 add_inbuf();
 123
 124         return count;
 125 }
 126 /*:*/
 127
 128 /*D:320 Console drivers are initialized very early so boot messages can go out,
 129  * so we do things slightly differently from the generic virtio initialization
 130  * of the net and block drivers.
 131  *
 132  * At this stage, the console is output-only.  It's too early to set up a
 133  * virtqueue, so we let the drivers do some boutique early-output thing. */
 134 int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int))
 135 {
 136         virtio_cons.put_chars = put_chars;
 137         return hvc_instantiate(0, 0, &virtio_cons);
 138 }
 139
 140 /*
 141  * we support only one console, the hvc struct is a global var
 142  * There is no need to do anything
 143  */
 144 static int notifier_add_vio(struct hvc_struct *hp, int data)
 145 {
 146         hp->irq_requested = 1;
 147         return 0;
 148 }
 149
 150 static void notifier_del_vio(struct hvc_struct *hp, int data)
 151 {
 152         hp->irq_requested = 0;
 153 }
 154
 155 static void hvc_handle_input(struct virtqueue *vq)
 156 {
 157         if (hvc_poll(hvc))
 158                 hvc_kick();
 159 }
 160
 161 /*D:370 Once we're further in boot, we get probed like any other virtio device.
 162  * At this stage we set up the output virtqueue.
 163  *
 164  * To set up and manage our virtual console, we call hvc_alloc().  Since we
 165  * never remove the console device we never need this pointer again.
 166  *
 167  * Finally we put our input buffer in the input queue, ready to receive. */
 168 static int __devinit virtcons_probe(struct virtio_device *dev)
 169 {
 170         int err;
 171
 172         vdev = dev;
 173
 174         /* This is the scratch page we use to receive console input */
 175         inbuf = kmalloc(PAGE_SIZE, GFP_KERNEL);
 176         if (!inbuf) {
 177                 err = -ENOMEM;
 178                 goto fail;
 179         }
 180
 181         /* Find the input queue. */
 182         /* FIXME: This is why we want to wean off hvc: we do nothing
 183          * when input comes in. */
 184         in_vq = vdev->config->find_vq(vdev, 0, hvc_handle_input);
 185         if (IS_ERR(in_vq)) {
 186                 err = PTR_ERR(in_vq);
 187                 goto free;
 188         }
 189
 190         out_vq = vdev->config->find_vq(vdev, 1, NULL);
 191         if (IS_ERR(out_vq)) {
 192                 err = PTR_ERR(out_vq);
 193                 goto free_in_vq;
 194         }
 195
 196         /* Start using the new console output. */
 197         virtio_cons.get_chars = get_chars;
 198         virtio_cons.put_chars = put_chars;
 199         virtio_cons.notifier_add = notifier_add_vio;
 200         virtio_cons.notifier_del = notifier_del_vio;
 201
 202         /* The first argument of hvc_alloc() is the virtual console number, so
 203          * we use zero.  The second argument is the parameter for the
 204          * notification mechanism (like irq number). We currently leave this
 205          * as zero, virtqueues have implicit notifications.
 206          *
 207          * The third argument is a "struct hv_ops" containing the put_chars()
 208          * get_chars(), notifier_add() and notifier_del() pointers.
 209          * The final argument is the output buffer size: we can do any size,
 210          * so we put PAGE_SIZE here. */
 211         hvc = hvc_alloc(0, 0, &virtio_cons, PAGE_SIZE);
 212         if (IS_ERR(hvc)) {
 213                 err = PTR_ERR(hvc);
 214                 goto free_out_vq;
 215         }
 216
 217         /* Register the input buffer the first time. */
 218         add_inbuf();
 219         return 0;
 220
 221 free_out_vq:
 222         vdev->config->del_vq(out_vq);
 223 free_in_vq:
 224         vdev->config->del_vq(in_vq);
 225 free:
 226         kfree(inbuf);
 227 fail:
 228         return err;
 229 }
 230
 231 static struct virtio_device_id id_table[] = {
 232         { VIRTIO_ID_CONSOLE, VIRTIO_DEV_ANY_ID },
 233         { 0 },
 234 };
 235
 236 static struct virtio_driver virtio_console = {
 237         .driver.name =  KBUILD_MODNAME,
 238         .driver.owner = THIS_MODULE,
 239         .id_table =     id_table,
 240         .probe =        virtcons_probe,
 241 };
 242
 243 static int __init init(void)
 244 {
 245         return register_virtio_driver(&virtio_console);
 246 }
 247 module_init(init);
 248
 249 MODULE_DEVICE_TABLE(virtio, id_table);
 250 MODULE_DESCRIPTION("Virtio console driver");
 251 MODULE_LICENSE("GPL");