^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) ==============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2) Serial Devices
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) ==============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) Serial Device Naming
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6) ====================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) As of 2.6.10, serial devices on ia64 are named based on the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) order of ACPI and PCI enumeration. The first device in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) ACPI namespace (if any) becomes /dev/ttyS0, the second becomes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11) /dev/ttyS1, etc., and PCI devices are named sequentially
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) starting after the ACPI devices.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14) Prior to 2.6.10, there were confusing exceptions to this:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) - Firmware on some machines (mostly from HP) provides an HCDP
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) table[1] that tells the kernel about devices that can be used
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18) as a serial console. If the user specified "console=ttyS0"
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) or the EFI ConOut path contained only UART devices, the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) kernel registered the device described by the HCDP as
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) /dev/ttyS0.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) - If there was no HCDP, we assumed there were UARTs at the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24) legacy COM port addresses (I/O ports 0x3f8 and 0x2f8), so
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) the kernel registered those as /dev/ttyS0 and /dev/ttyS1.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) Any additional ACPI or PCI devices were registered sequentially
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28) after /dev/ttyS0 as they were discovered.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30) With an HCDP, device names changed depending on EFI configuration
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) and "console=" arguments. Without an HCDP, device names didn't
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32) change, but we registered devices that might not really exist.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34) For example, an HP rx1600 with a single built-in serial port
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) (described in the ACPI namespace) plus an MP[2] (a PCI device) has
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36) these ports:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38) ========== ========== ============ ============ =======
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) Type MMIO pre-2.6.10 pre-2.6.10 2.6.10+
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40) address
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) (EFI console (EFI console
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42) on builtin) on MP port)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) ========== ========== ============ ============ =======
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) builtin 0xff5e0000 ttyS0 ttyS1 ttyS0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45) MP UPS 0xf8031000 ttyS1 ttyS2 ttyS1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) MP Console 0xf8030000 ttyS2 ttyS0 ttyS2
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47) MP 2 0xf8030010 ttyS3 ttyS3 ttyS3
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) MP 3 0xf8030038 ttyS4 ttyS4 ttyS4
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49) ========== ========== ============ ============ =======
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51) Console Selection
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) =================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) EFI knows what your console devices are, but it doesn't tell the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) kernel quite enough to actually locate them. The DIG64 HCDP
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) table[1] does tell the kernel where potential serial console
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) devices are, but not all firmware supplies it. Also, EFI supports
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) multiple simultaneous consoles and doesn't tell the kernel which
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59) should be the "primary" one.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61) So how do you tell Linux which console device to use?
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) - If your firmware supplies the HCDP, it is simplest to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64) configure EFI with a single device (either a UART or a VGA
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) card) as the console. Then you don't need to tell Linux
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) anything; the kernel will automatically use the EFI console.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68) (This works only in 2.6.6 or later; prior to that you had
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) to specify "console=ttyS0" to get a serial console.)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71) - Without an HCDP, Linux defaults to a VGA console unless you
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) specify a "console=" argument.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74) NOTE: Don't assume that a serial console device will be /dev/ttyS0.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) It might be ttyS1, ttyS2, etc. Make sure you have the appropriate
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76) entries in /etc/inittab (for getty) and /etc/securetty (to allow
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) root login).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) Early Serial Console
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) ====================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82) The kernel can't start using a serial console until it knows where
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) the device lives. Normally this happens when the driver enumerates
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84) all the serial devices, which can happen a minute or more after the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85) kernel starts booting.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87) 2.6.10 and later kernels have an "early uart" driver that works
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88) very early in the boot process. The kernel will automatically use
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89) this if the user supplies an argument like "console=uart,io,0x3f8",
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90) or if the EFI console path contains only a UART device and the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) firmware supplies an HCDP.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93) Troubleshooting Serial Console Problems
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) =======================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96) No kernel output after elilo prints "Uncompressing Linux... done":
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) - You specified "console=ttyS0" but Linux changed the device
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99) to which ttyS0 refers. Configure exactly one EFI console
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) device[3] and remove the "console=" option.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) - The EFI console path contains both a VGA device and a UART.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) EFI and elilo use both, but Linux defaults to VGA. Remove
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) the VGA device from the EFI console path[3].
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) - Multiple UARTs selected as EFI console devices. EFI and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) elilo use all selected devices, but Linux uses only one.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) Make sure only one UART is selected in the EFI console
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) path[3].
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) - You're connected to an HP MP port[2] but have a non-MP UART
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) selected as EFI console device. EFI uses the MP as a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) console device even when it isn't explicitly selected.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) Either move the console cable to the non-MP UART, or change
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) the EFI console path[3] to the MP UART.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) Long pause (60+ seconds) between "Uncompressing Linux... done" and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) start of kernel output:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) - No early console because you used "console=ttyS<n>". Remove
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121) the "console=" option if your firmware supplies an HCDP.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) - If you don't have an HCDP, the kernel doesn't know where
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) your console lives until the driver discovers serial
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125) devices. Use "console=uart,io,0x3f8" (or appropriate
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) address for your machine).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) Kernel and init script output works fine, but no "login:" prompt:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) - Add getty entry to /etc/inittab for console tty. Look for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) the "Adding console on ttyS<n>" message that tells you which
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) device is the console.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) "login:" prompt, but can't login as root:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) - Add entry to /etc/securetty for console tty.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) No ACPI serial devices found in 2.6.17 or later:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) - Turn on CONFIG_PNP and CONFIG_PNPACPI. Prior to 2.6.17, ACPI
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) serial devices were discovered by 8250_acpi. In 2.6.17,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) 8250_acpi was replaced by the combination of 8250_pnp and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143) CONFIG_PNPACPI.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) [1]
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148) http://www.dig64.org/specifications/agreement
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149) The table was originally defined as the "HCDP" for "Headless
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150) Console/Debug Port." The current version is the "PCDP" for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) "Primary Console and Debug Port Devices."
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153) [2]
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154) The HP MP (management processor) is a PCI device that provides
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 155) several UARTs. One of the UARTs is often used as a console; the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 156) EFI Boot Manager identifies it as "Acpi(HWP0002,700)/Pci(...)/Uart".
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 157) The external connection is usually a 25-pin connector, and a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 158) special dongle converts that to three 9-pin connectors, one of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 159) which is labelled "Console."
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 160)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 161) [3]
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 162) EFI console devices are configured using the EFI Boot Manager
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 163) "Boot option maintenance" menu. You may have to interrupt the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 164) boot sequence to use this menu, and you will have to reset the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 165) box after changing console configuration.
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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