Serial Over Lan (SOL) no login prompt on Linux IRQ mode

[akashgj]

I am using BMC Aspeed AST-2500 in our motherboard with OpenBMC firmware. 'obmc-console' is used to get host messages over BMC. obmc-console.conf looks like

lpc-address = 0x3f8
sirq = 4
local-tty = ttyS4
local-tty-baud = 115200

BIOS serial redirection is enabled over COM port 0 (0x3f8, sirq=4, baudrate=115200) for super-IO.

we set /dev/ttyS0 in CentOS to work in polling mode by making its irq=0 using the following command

$ setserial /dev/ttyS0 uart 16550a irq 0

Now we are getting CentOS login prompt on SOL.

When we change /dev/ttyS0 back to interrupt mode with irq=4, we are not getting login prompt on SOL.

[Kitsok]

I didn't try to set polling mode, but have the same: if VUART is used for host-BMC serial communications, it works only during POST stage.
Update: Just tried to enable polling mode via setserial and there is a communication via VUART.

[amboar]

There's a solution discussed in this thread:

https://lore.kernel.org/openbmc/20210727093015.GQ875@home.paul.comp/T/#m544ebf6b9177ed928d6a93ec2cee7be6c9a85ad2

Unfortunately lore didn't archive the message with the solution for the UART routing (possibly due to it being an HTML message), but it's available here:

https://lists.ozlabs.org/pipermail/openbmc/attachments/20210802/bfd7d272/attachment.htm

[Kitsok]

The recipe is the following:

1. In DTS disable UART1(ttyS0), UART2(ttyS1), enable UART3(ttyS2), UART4(ttyS3), disable VUART, enable uart_routing
2. In obmc-console prepare config server.ttyS3.conf with
   baud = 115200 local-tty = ttyS3 local-tty-baud = 115200
3. Set up routing via sysfs (UART1<->UART4)
   root@:/sys/devices/platform/ahb/ahb:apb/1e789000.lpc/1e78909c.uart_routing# echo -n uart4 > uart1 root@:/sys/devices/platform/ahb/ahb:apb/1e789000.lpc/1e78909c.uart_routing# echo -n uart1 > uart4 root@:/sys/devices/platform/ahb/ahb:apb/1e789000.lpc/1e78909c.uart_routing# cat uart* io1 io2 io3 io4 uart2 uart3 [uart4] io6 [io2] io3 io4 io1 uart3 uart4 uart1 io6 [io3] io4 io1 io2 uart4 uart1 uart2 io6 io4 io1 io2 io3 [uart1] uart2 uart3 io6 [io5] io1 io2 io3 io4 uart1 uart2 uart3 uart4 io6 root@:/sys/devices/platform/ahb/ahb:apb/1e789000.lpc/1e78909c.uart_routing#
4. Enable UART1 and 2 clocks either using devmem (wrong way)
   uart1_clock_en() { local val=$(devmem 0x1e6e200c) local val2=$(iotools and $val 0xffff7fff) devmem 0x1e6e200c w $val2 || : }
   or by patching kernel:
   `
   diff --git a/drivers/clk/clk-aspeed.c b/drivers/clk/clk-aspeed.c
   index bc8d130..a32502b 100644
   --- a/drivers/clk/clk-aspeed.c
   +++ b/drivers/clk/clk-aspeed.c
   @@ -67,8 +67,8 @@ static const struct aspeed_gate_data aspeed_gates[] = {
   [ASPEED_CLK_GATE_D1CLK] = { 10, 13, "d1clk-gate", NULL, 0 }, /* GFX CRT /
   [ASPEED_CLK_GATE_YCLK] = { 13, 4, "yclk-gate", NULL, 0 }, / HAC /
   [ASPEED_CLK_GATE_USBPORT1CLK] = { 14, 14, "usb-port1-gate", NULL, 0 }, / USB2 hub/USB2 host port 1/USB1.1 dev */

• [ASPEED_CLK_GATE_UART1CLK] = { 15, -1, "uart1clk-gate", "uart", 0 }, /* UART1 */
• [ASPEED_CLK_GATE_UART2CLK] = { 16, -1, "uart2clk-gate", "uart", 0 }, /* UART2 */

• [ASPEED_CLK_GATE_UART1CLK] = { 15, -1, "uart1clk-gate", "uart", CLK_IS_CRITICAL }, /* UART1 */
• [ASPEED_CLK_GATE_UART2CLK] = { 16, -1, "uart2clk-gate", "uart", CLK_IS_CRITICAL }, /* UART2 /
  [ASPEED_CLK_GATE_UART5CLK] = { 17, -1, "uart5clk-gate", "uart", 0 }, / UART5 /
  [ASPEED_CLK_GATE_ESPICLK] = { 19, -1, "espiclk-gate", NULL, 0 }, / eSPI /
  [ASPEED_CLK_GATE_MAC1CLK] = { 20, 11, "mac1clk-gate", "mac", 0 }, / MAC1 */
  --
  2.7.4

`
In latter case it is probably necessary to set up 0x1e6e200c register in U-Boot.
5. It is also vital to allow LPC reset of UART1 and UART2 from LPC, but in my case it's there by default.

In case you want to use VUART there are 2 ways:

1. In BIOS, before control is passed to OS loader, disable UART in SIO (not verified)
   or
2. In OS set UART driver polling mode using setserial irq 0.
   Hope this can help.

[amboar]

Fundamentally that all shouldn't be necessary. I haven't had the bandwidth to understand the problem and figure out what's going wrong.

The VUARTs work fine with interrupts on Power systems.