[PATCH] arm: amlogic: add setbrg op to serial device

[neil.armstrong at linaro.org]

Hi,

On 22/09/2022 20:51, Edoardo Tomelleri wrote:
> Hello,
> Il giorno gio 22 set 2022 alle ore 18:51 Neil Armstrong
> <neil.armstrong at linaro.org> ha scritto:
>>
>> Hi,
>>
>> Sorry for the delay...
> No problem, don't worry
> 
>> Looks good !
>>
>> If someone can test it ? otherwise I'll take it for next release.
> ...does it count if I've tested it? I have a radxa zero board (S905Y2
> chip), this started as an experimentation
> with editing register values in memory "for fun" and I decided to try
> to make a patch out of it.

Yes it's perfect, thanks a lot for the test results !

> I do not have an oscilloscope so I can not accurately measure the baud
> rate, but the logic is the same as
> in linux and using an USB to UART (PL2303) adapter console input and
> loady command work fine.
> I've just repeated a small test: I'm using picocom and lrzsz in ymodem
> mode under WSL, the usb adapter
> is forwarded to WSL using usbip, but this should not change anything
> at this kind of speed (I hope).
> Here are some results sending a 1 MB test file (created once from /dev/urandom):
> picocom v3.1
> 
> port is        : /dev/ttyUSB0
> flowcontrol    : none
> baudrate is    : 115200
> parity is      : none
> databits are   : 8
> stopbits are   : 1
> [...]
> send_cmd is    : sz --ymodem -vv
> receive_cmd is : rz -vv -E
> [...]
> @115200
> Bytes Sent:1048576   BPS:7762
> @230400
> Bytes Sent:1048576   BPS:16372
> @460800
> Bytes Sent:1048576   BPS:26681
> @500000
> Bytes Sent:1048576   BPS:27689
> @500000 (2nd run)
> Bytes Sent:1048576   BPS:27207
> 
> At this point I stopped testing, I think my adapter is not good enough
> and that the logic
> is correct (I've read amlogic's public datasheets [1], but I've not
> found a formula specified there),
> Reading address (for hardware device UARTAO1, that _of course_ is not
> listed there)
> md.l 0xff803014 1
> ff803014: 0180000f
> This corresponds to REG5 of device UARTAO1, with bits 24 (USE_XTAL_CLK), 23
> (use new baud rate) set, and bits 27 and 26 clear (so 24 MHz crystal
> clock is divided by 3),
> NEW_BAUD_RATE is f, so baud rate should be (8 MHz / (15 + 1)) = 500K.
> 
> Other than that, I noticed that setting the env variable baudrate is
> restricted to values allowed
> in a compile time config, loady is not and loady ignores the return
> value of meson_serial_setbrg
> (it returns -EINVAL if for example a baudrate higher than 8'000'000 is
> requested), here's a test
> (with env variable baudrate=500000):
> => loady 0x01000000 8000001
> ## Switch baudrate to 8000001 bps and press ENTER ...
> ## Ready for binary (ymodem) download to 0x01000000 at 8000001 bps...
> C
> *** file: ./dest
> $ sz --ymodem -vv ./dest
> Sending: dest
> Bytes Sent:1048576   BPS:27781
> Sending:
> Ymodem sectors/kbytes sent:   0/ 0k
> Transfer complete
> 
> *** exit status: 0 ***
> ## Total Size      = 0x00100000 = 1048576 Bytes
> ## Start Addr      = 0x01000000
> ## Switch baudrate to 500000 bps and press ESC ...
> =>
> 
> setbrg fails, the baud rate register is left at the 500'000 setting
> and that's it.
> I think the "for fun" experiment has gone a bit too far.
> 
> Edoardo
> [1] https://dl.radxa.com/zero/docs/hw/IO%20Interface%ef%bc%8dS905Y2%20Datasheet.pdf

I'll apply it then.

Acked-by: Neil Armstrong <narmstrong at baylibre.com>

Please send more patches with such quality !

Thanks,
Neil