Messages in this thread | | | From | Arnd Bergmann <> | Subject | Re: [PATCH] serial: 8250: Make ISA ports optional | Date | Tue, 06 Jan 2015 20:43:37 +0100 |
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On Tuesday 06 January 2015 09:32:02 Peter Hurley wrote: > On 01/06/2015 08:13 AM, Arnd Bergmann wrote: > > On Monday 05 January 2015 22:09:45 Peter Hurley wrote: > >> Some arches have no need to create unprobed 8250 ports; these phantom > >> ports are primarily required for ISA ports which have no probe > >> mechanism or to provide non-operational ports for userspace to > >> configure (via TIOCSSERIAL and TIOCSERCONFIG ioctls). > >> > >> Provide CONFIG_SERIAL_8250_PHANTOM_UARTS knob to disable phantom port > >> registration; ie., CONFIG_SERIAL_8250_PHANTOM_UARTS=N only registers > >> probed ports (ACPI/PNP, "serial8250" platform devices, PCI, etc). > >> > >> Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> > >> Cc: Tony Lindgren <tony@atomide.com> > >> Cc: Grant Likely <grant.likely@linaro.org> > >> Cc: Arnd Bergmann <arnd@arndb.de> > >> Signed-off-by: Peter Hurley <peter@hurleysoftware.com> > > > > The intent is definitely right, but I think a better approach is > > possible. > > > > I haven't tried it here, but how about moving the serial8250_init > > function into a separate module, along with all the other parts > > that are only used for ISA devices, but leaving the actual core > > (all exported symbols) in this file? > > Unfortunately, I don't see a way to remove the stacked initialization > without risking tons of breakage. > > Since later probes can "find" an already-existing port and > re-initialize it, the probe order is crucial. For example, a PCI > probe can "find" an existing "serial8250" platform device port, > resulting in only one device node.
I'm probably missing something important, by why would that be any different if the PCI driver gets loaded first and the ISA driver second?
> And the configuration knob will be required on all arches anyway because > that's how user-configurable device nodes are created.
I think that's fine: The user-configurable ports are the same as the "ISA" or "phantom" ports we were talking about above, right?
If those are part of a separate (possibly loadable) module, having a configuration knob is the obvious way to do it. A lot of architectures can just turn it off because they know exactly which ports are present and there is no need for user-configurability. The ones that don't know can load the module.
> > At the same time, the serial8250_pnp_init/serial8250_pnp_exit calls > > can be removed from the serial8250_init function and become > > standalone initcalls. > > PNP probe must occur before the phantom ports are registered. > See commit 835d844d1a28efba81d5aca7385e24c29d3a6db2 > ("8250_pnp: do pnp probe before legacy probe").
Makes sense.
Arnd
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