On 01/06/2015 02:43 PM, Arnd Bergmann wrote: > 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@xxxxxxxxxxxxx> >>>> Cc: Tony Lindgren <tony@xxxxxxxxxxx> >>>> Cc: Grant Likely <grant.likely@xxxxxxxxxx> >>>> Cc: Arnd Bergmann <arnd@xxxxxxxx> >>>> Signed-off-by: Peter Hurley <peter@xxxxxxxxxxxxxxxxxx> >>> >>> 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? Well, the PCI driver would have the proper irq, for one. So, if the the platform driver re-initialized the port to the wrong irq... >> 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? Yes. > 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. Let me give this some more thought. Regards, Peter Hurley -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
