[PATCH u-boot-marvell 00/13] Yet another kwboot improvements

[Stefan Roese]

On 26.10.21 15:06, Marek Behún wrote:
> On Tue, 26 Oct 2021 14:40:48 +0200
> Pali Rohár <pali at kernel.org> wrote:
> 
>> What is happening here? I do not know. But as Marek told me that
>> observed same issue and replacing USB-UART cable by another decreased
>> transfer time. So I think that issue is somewhere in USB-UART
>> transmitter. My guess is that USB-UART transmitter send at 921600 speed:
>> start bit, 8 bits of data, stop bit and then loooong idle pause (logical
>> one). After that sends another 10 bits.
> 
> Yes, my FT232RL USB-UART converters do not send at higher speeds,
> although they report baudrate change.
> 
> I do not really know what is going on. Maybe the ftdi-sio driver needs
> to be looked at. (It definitely needs to be looked at, because of other
> things. Last I looked into it the baudrate change code seemed okay.)
> 
> Using pl2303 converter works like a charm.
> 
> Note that I have another FT232RL converter for MOX, which works at
> 1.8V, and on MOX higher speeds work correctly.
> 
> Maybe some of the FT232RL chips are those fake ones?

Maybe. Unfortunately, on this Armada XP board this FTDI chip is soldered
on the target, so I can't easily switch adapters.

> Stefan, could you check in a different way whether your converter can
> transfer at higher speed? For example with another device, or in U-Boot
> via kermit / ymodem, or whatnot.

Connecting with 230400 baud and booting into U-Boot etc shows this:

$ cu -s 230400 -l 
/dev/serial/by-id/usb-FTDI_FT232R_USB_UART_A1019EGY-if00-port0
Connected.
�������������▒�����`�▒3������▒�▒�▒�▒30�▒0����`f憞~�▒���������f�`

So it seems, that baudrate change seems to work fine with the chip.

Thanks,
Stefan