[PATCH] serial: DCC(JTAG) serial and console emulation support

[Nicolas Pitre]

On Wed, 13 Oct 2010, Daniel Walker wrote:

> On Wed, 2010-10-13 at 19:44 +0200, Arnd Bergmann wrote:
> > On Wednesday 13 October 2010 18:17:03 Daniel Walker wrote:
> > > > I think you would be much better off making it a "hvc" driver, where
> > > > you just need to provide a read character and write character function
> > > > and an optional interrupt handler but otherwise have the common hvc
> > > > code take care of polling the hardware and talking to the tty layer.
> > > 
> > > I don't know what the "hvc" driver is "Hypervisor Virtual Console"
> > > maybe?
> > 
> > Yes, it originally was used only on hypervisors that had simple
> > read/write type consoles, but has now turned into a generic facility
> > that is used by a number of consoles that don't look like classic
> > serial ports.
> > 
> > > Can you give any sort of example driver which does what you
> > > suggesting?
> > 
> > Look at drivers/char/hvc_tile.c for the simplest case or
> > drivers/char/hvc_vio.c for one that uses interrupts.
> 
> I found it independently actually .. It looks like there's at least two
> problems. This jtag driver has a status register which flags when RX is
> available, and TX is possible. I'm not sure this status register fits
> into the model. The other thing is that we have a ttyJ registered for
> this driver, and it would be nice to use that over something like ttyHVC
> (I'm not sure if that name is correct, just a guess).

Really?  Is there a compelling reason to perpetuate this serial device 
namespace fragmentation nonsense?  Your initial patch even had a config 
option to hijack /dev/ttyS0 because of that.


Nicolas