drivers/misc/Makefile, Kconfig: cleanup
[linux-2.6/mini2440.git] / drivers / char / virtio_console.c
blob3fb0d2c88ba5fd3252bf7d773c8ecdaafc9de395
1 /*D:300
2 * The Guest console driver
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 :*/
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
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.
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.
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
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"
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;
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;
46 /* The operations for our console. */
47 static struct hv_ops virtio_cons;
49 /* The hvc device */
50 static struct hvc_struct *hvc;
52 /*D:310 The put_chars() callback is pretty straightforward.
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)
60 struct scatterlist sg[1];
61 unsigned int len;
63 /* This is a convenient routine to initialize a single-elem sg list */
64 sg_init_one(sg, buf, count);
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();
76 /* We're expected to return the amount of data we wrote: all of it. */
77 return count;
80 /* Create a scatter-gather list representing our input buffer and put it in the
81 * queue. */
82 static void add_inbuf(void)
84 struct scatterlist sg[1];
85 sg_init_one(sg, inbuf, PAGE_SIZE);
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);
93 /*D:350 get_chars() is the callback from the hvc_console infrastructure when
94 * an interrupt is received.
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)
101 /* If we don't have an input queue yet, we can't get input. */
102 BUG_ON(!in_vq);
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;
111 /* You want more than we have to give? Well, try wanting less! */
112 if (in_len < count)
113 count = in_len;
115 /* Copy across to their buffer and increment offset. */
116 memcpy(buf, in, count);
117 in += count;
118 in_len -= count;
120 /* Finished? Re-register buffer so Host will use it again. */
121 if (in_len == 0)
122 add_inbuf();
124 return count;
126 /*:*/
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.
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))
136 virtio_cons.put_chars = put_chars;
137 return hvc_instantiate(0, 0, &virtio_cons);
141 * we support only one console, the hvc struct is a global var
142 * There is no need to do anything
144 static int notifier_add_vio(struct hvc_struct *hp, int data)
146 hp->irq_requested = 1;
147 return 0;
150 static void notifier_del_vio(struct hvc_struct *hp, int data)
152 hp->irq_requested = 0;
155 static void hvc_handle_input(struct virtqueue *vq)
157 if (hvc_poll(hvc))
158 hvc_kick();
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.
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.
167 * Finally we put our input buffer in the input queue, ready to receive. */
168 static int __devinit virtcons_probe(struct virtio_device *dev)
170 int err;
172 vdev = dev;
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;
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;
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;
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 virtio_cons.notifier_hangup = notifier_del_vio;
203 /* The first argument of hvc_alloc() is the virtual console number, so
204 * we use zero. The second argument is the parameter for the
205 * notification mechanism (like irq number). We currently leave this
206 * as zero, virtqueues have implicit notifications.
208 * The third argument is a "struct hv_ops" containing the put_chars()
209 * get_chars(), notifier_add() and notifier_del() pointers.
210 * The final argument is the output buffer size: we can do any size,
211 * so we put PAGE_SIZE here. */
212 hvc = hvc_alloc(0, 0, &virtio_cons, PAGE_SIZE);
213 if (IS_ERR(hvc)) {
214 err = PTR_ERR(hvc);
215 goto free_out_vq;
218 /* Register the input buffer the first time. */
219 add_inbuf();
220 return 0;
222 free_out_vq:
223 vdev->config->del_vq(out_vq);
224 free_in_vq:
225 vdev->config->del_vq(in_vq);
226 free:
227 kfree(inbuf);
228 fail:
229 return err;
232 static struct virtio_device_id id_table[] = {
233 { VIRTIO_ID_CONSOLE, VIRTIO_DEV_ANY_ID },
234 { 0 },
237 static struct virtio_driver virtio_console = {
238 .driver.name = KBUILD_MODNAME,
239 .driver.owner = THIS_MODULE,
240 .id_table = id_table,
241 .probe = virtcons_probe,
244 static int __init init(void)
246 return register_virtio_driver(&virtio_console);
248 module_init(init);
250 MODULE_DEVICE_TABLE(virtio, id_table);
251 MODULE_DESCRIPTION("Virtio console driver");
252 MODULE_LICENSE("GPL");