powerpc: udbg based backend for hvc_console

[David Gibson]

On Thu, Nov 20, 2008 at 01:16:27PM -0600, Timur Tabi wrote:
> Milton Miller wrote:
> 
> > Stated differently, if your routine (1) fundamently works one character  
> > at a time and (2) is not interrupt driven, and (3) only supports one  
> > channel, what avantage is there to an explicit hvc driver?
> 
> I think it's because HVC has the ability to use HVC client drivers
> for console and TTY, but udbg does not.  So if you have a udbg-only
> driver, it will cease to function when the kernel switches to the
> normal console.
> 
> Perhaps it would make more sense to have the kernel continue to use udbg if
> there is no normal console driver, instead of relying on David's
> driver.

This doesn't work - the udbg console can't support a full tty driver
which is needed by userspace.  Originally, I was going to extend the
udbg console so that it supported a tty backended onto the udbg
methods.  Then I realised that the code I'd need to do this would be
essentially identical to hvconsole, so why duplicate it.

-- 
David Gibson			| I'll have my music baroque, and my code
david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
				| _way_ _around_!
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