Am 14.07.2015 um 19:22 schrieb Michał Pecio:
> I managed to reproduce this old issue, both on vanilla v4.1.1 and with
> my patch, IF and ONLY if I reverted commit 623c82633 by changing:
>
> - if (!old_termios || memcmp(buf, priv->line_settings, 7)) {
> ret = pl2303_set_line_request(port, buf);
> if (!ret)
> memcpy(priv->line_settings, buf, 7);
> - }
>
> I also added 'printk("Hello")' to pl2303_set_line_request.
>
> After that, spawning agetty on the pl2303, logging in through FTDI
> and listing a directory with two dozen files indeed outputs mangled
> filenames. Hello is printed twice for each ls.
>
> No problems happen with getty on FTDI and minicom on pl2303.
>
> The culprit seems to be bash, calling TCGETS/TCSETSW on its tty before
> and after every command to toggle some flags (echo, icanon, ...).
>
> Nothing bad happens with standard baud rates, i.e. bash still calls
> these ioctls, but there are no Hellos and no corruption.
>
> I also tried forcing divisor encoding on all baud rates with 623c82633
> reverted, like it was done back in the days of 3.12-rc. In this
> configuration, Hellos and corruptions happen for stardard baud rates
> if and only if the driver reports baud rate different than requested.
>
> In the end, my conlusions are as follows:
>
> 1. The corruption is caused by repeated attempts to set baud rate which
> can't be exactly realized. It has nothing to do with divisor encoding.
>
> 2. 623c82633 protects us no matter what bytes we send to the chip
> and what we return to the tty stack (until the userspace really sets a
> different rate).
>
> 3. Without 623c82633, we can only protect ourselves by lying about the
> actual rate. It seems that tty_termios_hw_change saves us in this case.
> That's why encode_direct and pre-57ce61aad748 encode_divisor work, but
> 57ce61aad748 failed. It came before 623c82633.
>
> Bottom line: my patch seems safe and fixes custom baud rates below 94k,
> which are completely screwed without it.
>
> The only thing I could imagine going wrong is chips which actually
> interpret baud rate settings the way described in the old comment.
>
> This definitely isn't my HX (rev A) nor my other HX knockoff.
>
> This also isn't whatever chips Frank Schäfer used during 57ce61aad748
> development.
100% correct.
> Finally, this probably isn't this comment author's chip either. I bet
> he wrote the comment and then randomly tweaked the code until it started
> working with actual hardware without realizing that the comment is wrong
> and doesn't describe the code anymore.
I assume he did some (incomplete) reverse-engineering.
The Windows driver (at that time) didn't support custom baud rates <
115k. ;)
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