Re: [patch 04/16] I/O driver for 8250-compatible UARTs

[Tom Rini]

On Wed, Aug 31, 2005 at 01:38:52PM -0600, Bjorn Helgaas wrote:
> On Monday 29 August 2005 10:09 am, Tom Rini wrote:
> >  linux-2.6.13-trini/drivers/serial/kgdb_8250.c  |  594 +++++++++++++++++++++
> 
> The existing stuff in drivers/serial is named "8250_*"; is
> there a reason you're using "kgdb_8250" rather than "8250_kgdb"?

All the other kgdb stuff tends to be prefixed, not suffixed.  But I
don't really care either way.

> > + *	serial8250_unregister_by_port - remove a 16x50 serial port
> > + *	at runtime.
> > + *	@port: A &struct uart_port that describes the port to remove.
> > + *
> > + *	Remove one serial port.  This may not be called from interrupt
> > + *	context.  We hand the port back to the our control.
> 
> Hand the port back to whose control?

Ok, that is non-sensical.  "We hand the port to the callers control." is
what I meant to say.

> > +MODULE_PARM_DESC(kgdb8250, " kgdb8250=<port number>,<baud rate>\n");
> 
> Document IRQ/MMIO/IOport stuff here too (whatever it turns out to be,
> see below).
> 
> It seems wrong to me to have kgdb8250 use "ttyS" names for devices.
> In general you don't know the ttyS name for a device until after the
> 8250 driver claims it.  Sure, it's a convenience to use "ttyS0"
> instead of "io,0x3f8", but it also makes it hard to run kgdb on a
> PCI or MMIO UART, because you don't know what its name will be.

I've tried intentionally to not mention 'ttyS' anywhere (exposed to the
user) because it's really not 'ttySN' but it is the port registered to
us.


> If you gave up the convenience and just always required an I/O port
> or MMIO address, you could nuke all the old_rs_table[] and
> kgdb8250_ports[] stuff, not to mention a bunch of config options.

But that's really rather handy so I'd rather not get rid of it.

There's really two cases we have to deal with.  The first case is a
known at compile time or can be registered at boot-time easily port (ie
dumb old PC or ARM boards).  The second case is "serial port over
there".  Perhaps we should change the kgdb8250 arg to be an override of
the default port, so:
kgdb8250={io,mmio},<irq>,<token>,<baud rate>

Would that work?

> > +static int kgdb8250_local_init(void)
> > +{
> > +	if (old_rs_table_copied == 0)
> > +		kgdb8250_copy_rs_table();
> 
> This would be easier to maintain if the "if (old_rs_table_copied)"
> test were in the callee, not in every caller.

I'm not sure.  In the compiled-in case we know it's always been run
prior to freeing __init data, and thus it's quasi-safe.  I suppose it
wouldn't be too big a deal to just remove the __init and do it like
that.

> > +	switch (CURRENTPORT.iotype) {
> > +	case UPIO_MEM:
> > +		if (CURRENTPORT.mapbase)
> > +			kgdb8250_needs_request_mem_region = 1;
> > +		if (CURRENTPORT.flags & UPF_IOREMAP) {
> > +			CURRENTPORT.membase = ioport_map(CURRENTPORT.mapbase,
> > +						      8 << KGDB8250_REG_SHIFT);
> 
> Shouldn't this be ioremap instead of ioport_map?

If I remember right from the testing, no.  Or if my memory is wrong and
that's retorihcal, sure.

> > +static int kgdb_init_io(void)
> > +{
> > +#ifdef CONFIG_KGDB_8250_MODULE
> > +	if (strlen(config)) {
> > +		if (kgdb8250_opt(config))
> > +			return -EINVAL;
> > +	} else {
> > +		printk(KERN_ERR "kgdb8250: argument error, usage: "
> > +		       "kgdb8250=<port number>,<baud rate>");
> > +#ifdef CONFIG_IA64
> > +		printk(",<irq>,<iomem base>");
> > +#endif
> 
> This isn't ia64-specific.

It is and it isn't.  Since no one's tried a PCI card uart for KGDB nor
had a case where we have to pass in the mmio addr except on ia64, it is
ia64-specific.  But as I said above, if we make kgdb8250= an override of
the compiled in choice, it wouldn't be.

> > +static void __init kgdb8250_hookup_irq(void)
> > +{
> > +#if defined(CONFIG_SERIAL_8250) || defined (CONFIG_SERIAL_8250_MODULE)
> > +	/* Take the port away from the main driver. */
> > +	serial8250_unregister_by_port(&CURRENTPORT);
> > +
> > +	/* Now reinit the port as the above has disabled things. */
> > +	kgdb8250_init();
> > +#endif
> > +	/* We may need to call request_mem_region() first. */
> > +	if (kgdb8250_needs_request_mem_region)
> > +		request_mem_region(CURRENTPORT.mapbase,
> > +				   8 << KGDB8250_REG_SHIFT, "kgdb");
> 
> The unregister/init/request_mem_region stuff doesn't sound very much
> like "hookup_irq".

All the stuff that's required before you can really hookup the IRQ.
Suggested name appricated.

> > + * Syntax for this cmdline option is "kgdb8250=ttyno,baudrate"
> > + * with ",irq,iomembase" tacked on the end on IA64.
> 
> This syntax doesn't really make sense on ia64, because there are
> no fixed "ttyno/iomembase" mappings.  It would be unambiguous to
> specify either ttyno OR iomembase, but there's no good way to use
> both.

It's true that ttyno isn't really useful on ia64.

> > +config KGDB_SIMPLE_SERIAL
> > +	bool "Simple selection of KGDB serial port"
> > +	depends on KGDB_8250
> > +	default y
> > +	help
> > +	  If you say Y here, you will only have to pick the baud rate
> > +	  and serial port (ttyS) that you wish to use for KGDB.  If you
> > +	  say N, you will have provide the I/O port and IRQ number.  Note
> > +	  that if your serial ports are iomapped, such as on ia64, then
> > +	  you must say Y here.  If in doubt, say Y.
> 
> How about: "... you will have to provide the address (I/O port or MMIO
> address) and IRQ ..."

I'd really rather not force everyone to pass in the address token and
IRQ#.

> I don't understand the "iomapped" bit -- does that mean MMIO?  And why
> would it make any difference whether they're in I/O port or MMIO space?

It's the special "boot once, figure out your I/O address and IRQ, reboot
and pass it in" case of IA64.  I'm under the impression that it's
because of the more dynamic than other arches that we couldn't just
register the ports as we find them to KGDB and let the user pick from a
pre-registered port that we play that game.

> I expect that if you use "ttyS" naming to select a port, that doesn't
> work early in boot on ia64, because ia64 doesn't have compiled-in
> knowledge of where ttyS devices live.  Is that related to what this is
> trying to say?

Yes.

> > +config KGDB_PORT
> > +	hex "hex I/O port address of the debug serial port"
> > +	depends on !KGDB_SIMPLE_SERIAL && KGDB_8250 && !IA64
> > +	default 3f8
> > +	help
> > +	  This is the unmapped (and on platforms with 1:1 mapping
> > +	  this is typically, but not always the same as the mapped)
> > +	  address of the serial port.  The stanards on your architecture
> > +	  may be found in include/asm-$(ARCH)/serial.h.
> 
> Not ia64-specific.  The description sounds like it applies to MMIO,
> not to I/O port space.    And s/stanards/standards/.

Having !mmio uarts on ia64 is news to me (but I've never used an ia64
box), hence the depends line.

> > +config KGDB_IRQ
> > +	int "IRQ of the debug serial port"
> > +	depends on !KGDB_SIMPLE_SERIAL && KGDB_8250 && !IA64
> > +	default 4
> > +	help
> > +	  This is the IRQ for the debug port.  This must be known so that
> > +	  KGDB can interrupt the running system (either for a new
> > +	  connection or when in gdb and control-C is issued).
> 
> Not ia64-specific.

True, don't recall why I did that one like that now, thanks.

-- 
Tom Rini
http://gate.crashing.org/~trini/
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