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 /*D:310 The put_chars() callback is pretty straightforward. 50 * 51 * We turn the characters into a scatter-gather list, add it to the output 52 * queue and then kick the Host. Then we sit here waiting for it to finish: 53 * inefficient in theory, but in practice implementations will do it 54 * immediately (lguest's Launcher does). */ 55 static int put_chars(u32 vtermno, const char *buf, int count) 56 { 57 struct scatterlist sg[1]; 58 unsigned int len; 59 60 /* This is a convenient routine to initialize a single-elem sg list */ 61 sg_init_one(sg, buf, count); 62 63 /* add_buf wants a token to identify this buffer: we hand it any 64 * non-NULL pointer, since there's only ever one buffer. */ 65 if (out_vq->vq_ops->add_buf(out_vq, sg, 1, 0, (void *)1) == 0) { 66 /* Tell Host to go! */ 67 out_vq->vq_ops->kick(out_vq); 68 /* Chill out until it's done with the buffer. */ 69 while (!out_vq->vq_ops->get_buf(out_vq, &len)) 70 cpu_relax(); 71 } 72 73 /* We're expected to return the amount of data we wrote: all of it. */ 74 return count; 75 } 76 77 /* Create a scatter-gather list representing our input buffer and put it in the 78 * queue. */ 79 static void add_inbuf(void) 80 { 81 struct scatterlist sg[1]; 82 sg_init_one(sg, inbuf, PAGE_SIZE); 83 84 /* We should always be able to add one buffer to an empty queue. */ 85 if (in_vq->vq_ops->add_buf(in_vq, sg, 0, 1, inbuf) != 0) 86 BUG(); 87 in_vq->vq_ops->kick(in_vq); 88 } 89 90 /*D:350 get_chars() is the callback from the hvc_console infrastructure when 91 * an interrupt is received. 92 * 93 * Most of the code deals with the fact that the hvc_console() infrastructure 94 * only asks us for 16 bytes at a time. We keep in_offset and in_used fields 95 * for partially-filled buffers. */ 96 static int get_chars(u32 vtermno, char *buf, int count) 97 { 98 /* If we don't have an input queue yet, we can't get input. */ 99 BUG_ON(!in_vq); 100 101 /* No buffer? Try to get one. */ 102 if (!in_len) { 103 in = in_vq->vq_ops->get_buf(in_vq, &in_len); 104 if (!in) 105 return 0; 106 } 107 108 /* You want more than we have to give? Well, try wanting less! */ 109 if (in_len < count) 110 count = in_len; 111 112 /* Copy across to their buffer and increment offset. */ 113 memcpy(buf, in, count); 114 in += count; 115 in_len -= count; 116 117 /* Finished? Re-register buffer so Host will use it again. */ 118 if (in_len == 0) 119 add_inbuf(); 120 121 return count; 122 } 123 /*:*/ 124 125 /*D:320 Console drivers are initialized very early so boot messages can go out, 126 * so we do things slightly differently from the generic virtio initialization 127 * of the net and block drivers. 128 * 129 * At this stage, the console is output-only. It's too early to set up a 130 * virtqueue, so we let the drivers do some boutique early-output thing. */ 131 int __init virtio_cons_early_init(int (*put_chars)(u32, const char *, int)) 132 { 133 virtio_cons.put_chars = put_chars; 134 return hvc_instantiate(0, 0, &virtio_cons); 135 } 136 137 /*D:370 Once we're further in boot, we get probed like any other virtio device. 138 * At this stage we set up the output virtqueue. 139 * 140 * To set up and manage our virtual console, we call hvc_alloc(). Since we 141 * never remove the console device we never need this pointer again. 142 * 143 * Finally we put our input buffer in the input queue, ready to receive. */ 144 static int __devinit virtcons_probe(struct virtio_device *dev) 145 { 146 int err; 147 struct hvc_struct *hvc; 148 149 vdev = dev; 150 151 /* This is the scratch page we use to receive console input */ 152 inbuf = kmalloc(PAGE_SIZE, GFP_KERNEL); 153 if (!inbuf) { 154 err = -ENOMEM; 155 goto fail; 156 } 157 158 /* Find the input queue. */ 159 /* FIXME: This is why we want to wean off hvc: we do nothing 160 * when input comes in. */ 161 in_vq = vdev->config->find_vq(vdev, NULL); 162 if (IS_ERR(in_vq)) { 163 err = PTR_ERR(in_vq); 164 goto free; 165 } 166 167 out_vq = vdev->config->find_vq(vdev, NULL); 168 if (IS_ERR(out_vq)) { 169 err = PTR_ERR(out_vq); 170 goto free_in_vq; 171 } 172 173 /* Start using the new console output. */ 174 virtio_cons.get_chars = get_chars; 175 virtio_cons.put_chars = put_chars; 176 177 /* The first argument of hvc_alloc() is the virtual console number, so 178 * we use zero. The second argument is the interrupt number; we 179 * currently leave this as zero: it would be better not to use the 180 * hvc mechanism and fix this (FIXME!). 181 * 182 * The third argument is a "struct hv_ops" containing the put_chars() 183 * and get_chars() pointers. The final argument is the output buffer 184 * size: we can do any size, so we put PAGE_SIZE here. */ 185 hvc = hvc_alloc(0, 0, &virtio_cons, PAGE_SIZE); 186 if (IS_ERR(hvc)) { 187 err = PTR_ERR(hvc); 188 goto free_out_vq; 189 } 190 191 /* Register the input buffer the first time. */ 192 add_inbuf(); 193 return 0; 194 195 free_out_vq: 196 vdev->config->del_vq(out_vq); 197 free_in_vq: 198 vdev->config->del_vq(in_vq); 199 free: 200 kfree(inbuf); 201 fail: 202 return err; 203 } 204 205 static struct virtio_device_id id_table[] = { 206 { VIRTIO_ID_CONSOLE, VIRTIO_DEV_ANY_ID }, 207 { 0 }, 208 }; 209 210 static struct virtio_driver virtio_console = { 211 .driver.name = KBUILD_MODNAME, 212 .driver.owner = THIS_MODULE, 213 .id_table = id_table, 214 .probe = virtcons_probe, 215 }; 216 217 static int __init init(void) 218 { 219 return register_virtio_driver(&virtio_console); 220 } 221 module_init(init); 222 223 MODULE_DEVICE_TABLE(virtio, id_table); 224 MODULE_DESCRIPTION("Virtio console driver"); 225 MODULE_LICENSE("GPL"); 226