On Tue, 26 Oct 2021 14:40:48 +0200 Pali Rohár pali@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?
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.
Marek