I spent several hours today trying to find a solution for this to no avail. Perhaps I didn't have the right search words.
There are three uart devices on my Banana Pro after boot. uart0, /dev/ttyS0, is reserved for terminal comm but I should be able to use uart4, /dev/ttyS1 and uart7, /dev/ttyS1, for other things, however, only /dev/ttyS0 is enabled at boot.
Code:
rick@bpro10:~$ dmesg | grep tty
[ 0.000000] Kernel command line: console=ttyS0,115200n8 TERM=screen-256color root=/dev/sda1 waitforroot=3 rootfstype=ext4
[ 0.954485] console [ttyS0] disabled
[ 0.974724] 1c28000.serial: ttyS0 at MMIO 0x1c28000 (irq = 45, base_baud = 1500000) is a U6_16550A
[ 1.671234] console [ttyS0] enabled
[ 1.698214] 1c29000.serial: ttyS1 at MMIO 0x1c29000 (irq = 46, base_baud = 1500000) is a U6_16550A
[ 1.730585] 1c29c00.serial: ttyS2 at MMIO 0x1c29c00 (irq = 47, base_baud = 1500000) is a U6_16550A
root@bpro10:/home/rick# cat /proc/tty/driver/serial
serinfo:1.0 driver revision:
0: uart:U6_16550A mmio:0x01C28000 irq:45 tx:8684 rx:0 RTS|DTR
1: uart:U6_16550A mmio:0x01C29000 irq:46 tx:0 rx:0
2: uart:U6_16550A mmio:0x01C29C00 irq:47 tx:0 rx:0
I decompiled sun7i-a20-bananapro.dtb with dtc and had a squiz. The nodes in the dts file for uart4 and uart7 seem complete and correct when compared with the corresponding uart0 nodes and all three are set "status = "okay"; and not "status = "disabled";"
This leads me to thinks that there is something else I need to do to enable /dev/ttyS1 and /dev/ttyS2 but I have yet to find or figure out what to do.