Re: [PATCH V3 5/7] serial: earlycon: Set UPIO_MEM32BE based on DT properties

[Peter Hurley <peter-WaGBZJeGNqdsbIuE7sb01tBPR1lH4CV8@public.gmane.org>]

On 03/28/2015 03:28 PM, Kevin Cernekee wrote:
> Side note:
> 
> AFAIK we still have a problem if somebody wants to build serial8250 +
> (any other tty driver that occupies major 4 / minor 64) into the same
> kernel, and use DT to pick the correct driver at runtime.

Yep, exactly.

> serial8250_init() starts registering ports before it knows whether the
> system even has an 8250.

This behavior is required to support hw configuration from userspace.

> I talked to Rob about it earlier this week
> and he suggested that you might have some thoughts on how to fix it.
 
A big piece of that will land in 4.01 (once I get the actual 8250 split
commit to Greg).

The 8250 driver has been split into a legacy/universal 8250 driver
and separate port ops module; one of the benefits of this is that the
objectionable legacy behavior of the 8250 driver (especially limitations
wrt ttyS sharing) can be left behind in that driver without breaking
existing users.

The idea is that an alternate 8250 driver(s) with none of the legacy
baggage can be taught to share (4,64) ports with other drivers.
Unfortunately, I haven't made further progress with because of other
projects.

Regards,
Peter Hurley




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