2 * The Guest console driver
4 * This is a trivial console driver: we use lguest's DMA mechanism to send
5 * bytes out, and register a DMA buffer to receive bytes in. It is assumed to
6 * be present and available from the very beginning of boot.
8 * Writing console drivers is one of the few remaining Dark Arts in Linux.
9 * Fortunately for us, the path of virtual consoles has been well-trodden by
10 * the PowerPC folks, who wrote "hvc_console.c" to generically support any
11 * virtual console. We use that infrastructure which only requires us to write
12 * the basic put_chars and get_chars functions and call the right register
16 /* Copyright (C) 2006 Rusty Russell, IBM Corporation
18 * This program is free software; you can redistribute it and/or modify
19 * it under the terms of the GNU General Public License as published by
20 * the Free Software Foundation; either version 2 of the License, or
21 * (at your option) any later version.
23 * This program is distributed in the hope that it will be useful,
24 * but WITHOUT ANY WARRANTY; without even the implied warranty of
25 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
26 * GNU General Public License for more details.
28 * You should have received a copy of the GNU General Public License
29 * along with this program; if not, write to the Free Software
30 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307 USA
32 #include <linux/err.h>
33 #include <linux/init.h>
34 #include <linux/lguest_bus.h>
35 #include "hvc_console.h"
37 /*D:340 This is our single console input buffer, with associated "struct
38 * lguest_dma" referring to it. Note the 0-terminated length array, and the
39 * use of physical address for the buffer itself. */
40 static char inbuf[256];
41 static struct lguest_dma cons_input = { .used_len = 0,
42 .addr[0] = __pa(inbuf),
43 .len[0] = sizeof(inbuf),
46 /*D:310 The put_chars() callback is pretty straightforward.
48 * First we put the pointer and length in a "struct lguest_dma": we only have
49 * one pointer, so we set the second length to 0. Then we use SEND_DMA to send
50 * the data to (Host) buffers attached to the console key. Usually a device's
51 * key is a physical address within the device's memory, but because the
52 * console device doesn't have any associated physical memory, we use the
53 * LGUEST_CONSOLE_DMA_KEY constant (aka 0). */
54 static int put_chars(u32 vtermno, const char *buf, int count)
56 struct lguest_dma dma;
58 /* FIXME: DMA buffers in a "struct lguest_dma" are not allowed
59 * to go over page boundaries. This never seems to happen,
60 * but if it did we'd need to fix this code. */
63 dma.addr[0] = __pa(buf);
65 lguest_send_dma(LGUEST_CONSOLE_DMA_KEY, &dma);
66 /* We're expected to return the amount of data we wrote: all of it. */
70 /*D:350 get_chars() is the callback from the hvc_console infrastructure when
71 * an interrupt is received.
73 * Firstly we see if our buffer has been filled: if not, we return. The rest
74 * of the code deals with the fact that the hvc_console() infrastructure only
75 * asks us for 16 bytes at a time. We keep a "cons_offset" variable for
76 * partially-read buffers. */
77 static int get_chars(u32 vtermno, char *buf, int count)
79 static int cons_offset;
81 /* Nothing left to see here... */
82 if (!cons_input.used_len)
85 /* You want more than we have to give? Well, try wanting less! */
86 if (cons_input.used_len - cons_offset < count)
87 count = cons_input.used_len - cons_offset;
89 /* Copy across to their buffer and increment offset. */
90 memcpy(buf, inbuf + cons_offset, count);
93 /* Finished? Zero offset, and reset cons_input so Host will use it
95 if (cons_offset == cons_input.used_len) {
97 cons_input.used_len = 0;
103 static struct hv_ops lguest_cons = {
104 .get_chars = get_chars,
105 .put_chars = put_chars,
108 /*D:320 Console drivers are initialized very early so boot messages can go
109 * out. At this stage, the console is output-only. Our driver checks we're a
110 * Guest, and if so hands hvc_instantiate() the console number (0), priority
111 * (0), and the struct hv_ops containing the put_chars() function. */
112 static int __init cons_init(void)
114 if (strcmp(paravirt_ops.name, "lguest") != 0)
117 return hvc_instantiate(0, 0, &lguest_cons);
119 console_initcall(cons_init);
121 /*D:370 To set up and manage our virtual console, we call hvc_alloc() and
122 * stash the result in the private pointer of the "struct lguest_device".
123 * Since we never remove the console device we never need this pointer again,
124 * but using ->private is considered good form, and you never know who's going
125 * to copy your driver.
127 * Once the console is set up, we bind our input buffer ready for input. */
128 static int lguestcons_probe(struct lguest_device *lgdev)
132 /* The first argument of hvc_alloc() is the virtual console number, so
133 * we use zero. The second argument is the interrupt number.
135 * The third argument is a "struct hv_ops" containing the put_chars()
136 * and get_chars() pointers. The final argument is the output buffer
137 * size: we use 256 and expect the Host to have room for us to send
139 lgdev->private = hvc_alloc(0, lgdev_irq(lgdev), &lguest_cons, 256);
140 if (IS_ERR(lgdev->private))
141 return PTR_ERR(lgdev->private);
143 /* We bind a single DMA buffer at key LGUEST_CONSOLE_DMA_KEY.
144 * "cons_input" is that statically-initialized global DMA buffer we saw
145 * above, and we also give the interrupt we want. */
146 err = lguest_bind_dma(LGUEST_CONSOLE_DMA_KEY, &cons_input, 1,
149 printk("lguest console: failed to bind buffer.\n");
152 /* Note the use of lgdev_irq() for the interrupt number. We tell hvc_alloc()
153 * to expect input when this interrupt is triggered, and then tell
154 * lguest_bind_dma() that is the interrupt to send us when input comes in. */
156 /*D:360 From now on the console driver follows standard Guest driver form:
157 * register_lguest_driver() registers the device type and probe function, and
158 * the probe function sets up the device.
160 * The standard "struct lguest_driver": */
161 static struct lguest_driver lguestcons_drv = {
162 .name = "lguestcons",
163 .owner = THIS_MODULE,
164 .device_type = LGUEST_DEVICE_T_CONSOLE,
165 .probe = lguestcons_probe,
168 /* The standard init function */
169 static int __init hvc_lguest_init(void)
171 return register_lguest_driver(&lguestcons_drv);
173 module_init(hvc_lguest_init);