boot2/loader: serial port handling

[Xin Li]

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On 10/12/12 17:04, Garrett Cooper wrote:
> On Fri, Oct 12, 2012 at 4:30 PM, Xin Li <delphij at delphij.net>
> wrote:
>> Hi,
>> 
>> We have some rather hacky quick hack at $WORK that addresses a
>> problem we have found with boot2/loader and wants to share it and
>> see if we can have more neat solution.
>> 
>> Here is the problem: the current boot2 and loader have various
>> places where it considers serial port to exist.  When the port is
>> not there, the code would hang because it tests whether the
>> hardware's -READY bit, basically something like:
>> 
>> do { } while (inpb(state register) & READY_BIT);
>> 
>> This unfortunately would enter an infinite loop when the device
>> is not present -- all in operations would get all bits set.
>> 
>> To reproduce this, one can compile boot2/loader with non-existent
>> port and the system will hang at very early stage of boot.
>> 
>> ---
>> 
>> Because boot2 is size constrained we can not use very
>> sophisticated detection logic there, what I did is to use
>> something like:
>> 
>> outb(line control register, word) if (inb(line control register)
>> != word) Disable the serial port read/write
>> 
>> For loader I'm not sure if we should use better detection logic.
>> By the way, it seems that the system may force using the default
>> console in loader regardless if the detection logic said no, if
>> it decides that's the only usable one.
>> 
>> So what would be the right way to solve these issue?
> 
> Have you tried out Andriy's commit yet to loader(8) (r241301)?

Ah I wish I am not this far behind my email backlog.  Yes I think
these (241300 and 241301) will solve the problem.

Cheers,
- -- 
Xin LI <delphij at delphij.net>    https://www.delphij.net/
FreeBSD - The Power to Serve!           Live free or die
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