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Commit | Line | Data |
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1da177e4 LT |
1 | SERIAL DEVICE NAMING |
2 | ||
3 | As of 2.6.10, serial devices on ia64 are named based on the | |
4 | order of ACPI and PCI enumeration. The first device in the | |
5 | ACPI namespace (if any) becomes /dev/ttyS0, the second becomes | |
6 | /dev/ttyS1, etc., and PCI devices are named sequentially | |
7 | starting after the ACPI devices. | |
8 | ||
9 | Prior to 2.6.10, there were confusing exceptions to this: | |
10 | ||
11 | - Firmware on some machines (mostly from HP) provides an HCDP | |
12 | table[1] that tells the kernel about devices that can be used | |
13 | as a serial console. If the user specified "console=ttyS0" | |
14 | or the EFI ConOut path contained only UART devices, the | |
15 | kernel registered the device described by the HCDP as | |
16 | /dev/ttyS0. | |
17 | ||
18 | - If there was no HCDP, we assumed there were UARTs at the | |
19 | legacy COM port addresses (I/O ports 0x3f8 and 0x2f8), so | |
20 | the kernel registered those as /dev/ttyS0 and /dev/ttyS1. | |
21 | ||
22 | Any additional ACPI or PCI devices were registered sequentially | |
23 | after /dev/ttyS0 as they were discovered. | |
24 | ||
25 | With an HCDP, device names changed depending on EFI configuration | |
26 | and "console=" arguments. Without an HCDP, device names didn't | |
27 | change, but we registered devices that might not really exist. | |
28 | ||
29 | For example, an HP rx1600 with a single built-in serial port | |
30 | (described in the ACPI namespace) plus an MP[2] (a PCI device) has | |
31 | these ports: | |
32 | ||
33 | pre-2.6.10 pre-2.6.10 | |
34 | MMIO (EFI console (EFI console | |
35 | address on builtin) on MP port) 2.6.10 | |
36 | ========== ========== ========== ====== | |
37 | builtin 0xff5e0000 ttyS0 ttyS1 ttyS0 | |
38 | MP UPS 0xf8031000 ttyS1 ttyS2 ttyS1 | |
39 | MP Console 0xf8030000 ttyS2 ttyS0 ttyS2 | |
40 | MP 2 0xf8030010 ttyS3 ttyS3 ttyS3 | |
41 | MP 3 0xf8030038 ttyS4 ttyS4 ttyS4 | |
42 | ||
43 | CONSOLE SELECTION | |
44 | ||
45 | EFI knows what your console devices are, but it doesn't tell the | |
46 | kernel quite enough to actually locate them. The DIG64 HCDP | |
47 | table[1] does tell the kernel where potential serial console | |
48 | devices are, but not all firmware supplies it. Also, EFI supports | |
49 | multiple simultaneous consoles and doesn't tell the kernel which | |
50 | should be the "primary" one. | |
51 | ||
52 | So how do you tell Linux which console device to use? | |
53 | ||
54 | - If your firmware supplies the HCDP, it is simplest to | |
55 | configure EFI with a single device (either a UART or a VGA | |
56 | card) as the console. Then you don't need to tell Linux | |
57 | anything; the kernel will automatically use the EFI console. | |
58 | ||
59 | (This works only in 2.6.6 or later; prior to that you had | |
60 | to specify "console=ttyS0" to get a serial console.) | |
61 | ||
62 | - Without an HCDP, Linux defaults to a VGA console unless you | |
63 | specify a "console=" argument. | |
64 | ||
65 | NOTE: Don't assume that a serial console device will be /dev/ttyS0. | |
66 | It might be ttyS1, ttyS2, etc. Make sure you have the appropriate | |
67 | entries in /etc/inittab (for getty) and /etc/securetty (to allow | |
68 | root login). | |
69 | ||
70 | EARLY SERIAL CONSOLE | |
71 | ||
72 | The kernel can't start using a serial console until it knows where | |
73 | the device lives. Normally this happens when the driver enumerates | |
74 | all the serial devices, which can happen a minute or more after the | |
75 | kernel starts booting. | |
76 | ||
77 | 2.6.10 and later kernels have an "early uart" driver that works | |
78 | very early in the boot process. The kernel will automatically use | |
79 | this if the user supplies an argument like "console=uart,io,0x3f8", | |
80 | or if the EFI console path contains only a UART device and the | |
81 | firmware supplies an HCDP. | |
82 | ||
83 | TROUBLESHOOTING SERIAL CONSOLE PROBLEMS | |
84 | ||
85 | No kernel output after elilo prints "Uncompressing Linux... done": | |
86 | ||
87 | - You specified "console=ttyS0" but Linux changed the device | |
88 | to which ttyS0 refers. Configure exactly one EFI console | |
89 | device[3] and remove the "console=" option. | |
90 | ||
91 | - The EFI console path contains both a VGA device and a UART. | |
92 | EFI and elilo use both, but Linux defaults to VGA. Remove | |
93 | the VGA device from the EFI console path[3]. | |
94 | ||
95 | - Multiple UARTs selected as EFI console devices. EFI and | |
96 | elilo use all selected devices, but Linux uses only one. | |
97 | Make sure only one UART is selected in the EFI console | |
98 | path[3]. | |
99 | ||
100 | - You're connected to an HP MP port[2] but have a non-MP UART | |
101 | selected as EFI console device. EFI uses the MP as a | |
102 | console device even when it isn't explicitly selected. | |
103 | Either move the console cable to the non-MP UART, or change | |
104 | the EFI console path[3] to the MP UART. | |
105 | ||
106 | Long pause (60+ seconds) between "Uncompressing Linux... done" and | |
107 | start of kernel output: | |
108 | ||
109 | - No early console because you used "console=ttyS<n>". Remove | |
110 | the "console=" option if your firmware supplies an HCDP. | |
111 | ||
112 | - If you don't have an HCDP, the kernel doesn't know where | |
113 | your console lives until the driver discovers serial | |
114 | devices. Use "console=uart, io,0x3f8" (or appropriate | |
115 | address for your machine). | |
116 | ||
117 | Kernel and init script output works fine, but no "login:" prompt: | |
118 | ||
119 | - Add getty entry to /etc/inittab for console tty. Look for | |
120 | the "Adding console on ttyS<n>" message that tells you which | |
121 | device is the console. | |
122 | ||
123 | "login:" prompt, but can't login as root: | |
124 | ||
125 | - Add entry to /etc/securetty for console tty. | |
126 | ||
1ab54a93 BH |
127 | No ACPI serial devices found in 2.6.17 or later: |
128 | ||
129 | - Turn on CONFIG_PNP and CONFIG_PNPACPI. Prior to 2.6.17, ACPI | |
130 | serial devices were discovered by 8250_acpi. In 2.6.17, | |
131 | 8250_acpi was replaced by the combination of 8250_pnp and | |
132 | CONFIG_PNPACPI. | |
133 | ||
1da177e4 LT |
134 | |
135 | ||
136 | [1] http://www.dig64.org/specifications/DIG64_PCDPv20.pdf | |
137 | The table was originally defined as the "HCDP" for "Headless | |
138 | Console/Debug Port." The current version is the "PCDP" for | |
139 | "Primary Console and Debug Port Devices." | |
140 | ||
141 | [2] The HP MP (management processor) is a PCI device that provides | |
142 | several UARTs. One of the UARTs is often used as a console; the | |
143 | EFI Boot Manager identifies it as "Acpi(HWP0002,700)/Pci(...)/Uart". | |
144 | The external connection is usually a 25-pin connector, and a | |
145 | special dongle converts that to three 9-pin connectors, one of | |
146 | which is labelled "Console." | |
147 | ||
148 | [3] EFI console devices are configured using the EFI Boot Manager | |
149 | "Boot option maintenance" menu. You may have to interrupt the | |
150 | boot sequence to use this menu, and you will have to reset the | |
151 | box after changing console configuration. |