Re: [PATCH] PowerPC: Fix find_legacy_serial_ports on OPB.

[David Gibson <dwg@au1.ibm.com>]

On Thu, Oct 11, 2007 at 01:31:53PM -0500, Josh Boyer wrote:
> On Thu, 2007-10-11 at 21:26 +0400, Valentine Barshak wrote:
> > Josh Boyer wrote:
> > > On Thu, 2007-10-11 at 17:50 +0200, Arnd Bergmann wrote:
> > >> On Thursday 11 October 2007, Valentine Barshak wrote:
> > >>> Currently find_legacy_serial_ports() can find no serial ports on the OPB.
> > >>> Thus no legacy boot console can be initialized. Just the early udbg console
> > >>> works, which is initialized with udbg_init_44x_as1() on the UART's physical
> > >>> address specified in kernel config. This happens because we look for ns16750
> > >>> and higher serial devices only and expect opb node to have a device type
> > >>> property. This patch makes it look for ns16550 compatible devices and use
> > >>> of_device_is_compatible() for opb instead of checking device type.
> > >>> Lack of legacy serial ports found causes problems for KGDB over serial.
> > >>>
> > >>> Signed-off-by: Valentine Barshak <vbarshak@ru.mvista.com>
> > >> The patch would make sense if we were only dealing with flattened device
> > >> tree systems at this point. Unfortunately, IBM is shipping hardware that
> > >> encodes the serial port in exactly the way that find_legacy_serial_ports
> > >> is looking for (parent->type == "opb", compatible = "ns16750" "ns16550"
> > >> "ns16450" i8250").
> > >>
> > >> Changing the search for ns16750 to ns16550 should be fine, but unnecessary
> > >> because AFAIK, all OPB serial imlpementations are actually ns16750 and
> > >> should have that in the device tree as well.
> > >>
> > >> For the device type of the bus, please check for both compatible and
> > >> type, so that it still works on machines that are missing the compatible
> > >> property.
> > > 
> > > Wait, no.  We already had this discussion months ago when David was
> > > working on the original Ebony port.  It was declared that legacy_serial
> > > is not how serial should be done on 4xx and the serial_of driver was
> > > supposed to be used instead.
> > > 
> > > Have we changed our stance on that?  If not, then perhaps KGDB should be
> > > fixed to work with serial_of.
> > 
> > Actually I don't see any reason not to use legacy_serial stuff for early 
> > console. We could split the kernel configured very early debug output, 
> > which uses  PPC_EARLY_DEBUG_44x_PHYSLOW/PHYSHIGH (since it's really 
> > dangerous) and early console things by using legacy serial. We could use 
> >   early boot console without PPC_EARLY_DEBUG_44x.
> 
> That was exactly my thinking when this first came up.  I'd like to hear
> David's opinion on it.

Yeah, I think I misinterpreted BenH way back when.  This looks ok, and
means serial will be initialized earlier than of_serial, which would
be nice.

-- 
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_!
http://www.ozlabs.org/~dgibson