On Fri, Oct 23, 2015 at 10:37:49AM -0500, Timur Tabi wrote:
> On 10/23/2015 08:34 AM, Dave P Martin wrote:
> >Well, I'm not saying there's definitely no kernel bug, but I can't see
> >how the patch should cause it. It may be triggering a latent bug
> >somewhere else in the driver than hasn't been biting us before, however.
>
> Fair enough.
>
> >!CREAD is the most obvious cause, so that should definitely be ruled
> >out first. If CREAD is clear, we need to figure out why...
>
> So I tested this by booting to my console, and then typing in:
>
> stty -cread
>
> and when I did that, the console ignored all input.
>
> I do admit that since !CREAD has been ignored for so many reason, it
> could be that a lot of userspaces will suddenly have broken
> consoles.
I'm pretty sure CREAD should default to enabled[1], and that usually
software won't modify it.
Assuming that this is indeed the problem, it's possible that another bug
in the pl011 driver is wrongly clearing this flag. Sadly I don't have
time to look at the code again just now ... :(
Could be interesting to stick some BUG_ON(!CREAD) in the driver to
try and track down where that's coming from.
Cheers
---Dave
[1] See serial_core.c:uart_register_driver(),
serial_core.c:uart_set_options().
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