[PATCH v3 0/3] serial: Support a disabled serial port

[Tom Rini]

On Wed, Nov 20, 2024 at 05:37:35PM +0100, Caleb Connolly wrote:
> 
> 
> On 20/11/2024 17:03, Simon Glass wrote:
> > Hi Caleb,
> > 
> > On Wed, 20 Nov 2024 at 08:56, Caleb Connolly <caleb.connolly at linaro.org> wrote:
> >>
> >> Hi Simon,
> >>
> >> On 20/11/2024 16:35, Simon Glass wrote:
> >>> This series provides a way to tell a serial UART that it can't actually
> >>> work, at runtime. The main motivation is to deal with a coreboot feature
> >>> where it does not provide UART details in the sysinfo structure unless
> >>> the UART is also enabled in coreboot.
> >>
> >> Why is the UART driver probed if coreboot doesn't provide the necessary
> >> info for it?
> > 
> > U-Boot doesn't do well without some sort of serial device. That could
> > perhaps be improved. But the point here is that we need a single
> > U-Boot build which can start from coreboot, regardless of what
> > coreboot decides to do.
> 
> Right, I'm suggesting that at runtime you notice that coreboot didn't
> provide a serial port definition (or gave you a bogus address or
> something) and skip probing the serial port in that case.
> > 
> >>
> >> Couldn't you disable CONFIG_REQUIRE_SERIAL_CONSOLE and skip probing it?
> > 
> > No, because I want it to work if the serial info is available.
> 
> This option doesn't disable the serial port, it just makes U-Boot not
> panic if it can't find one. For example I enable this when building
> U-Boot for the upstream supported Qualcomm phones since many don't
> enable the serial port in their DTS.

Yes, this feels like an oddly coreboot specific solution to a generic
problem that we should be able to handle already I thought? Like a Pi
can have or not have a serial port enabled and still have video and we
use that. We might well need something specific to know the port is
disabled since I gather we aren't getting a devicetree that says status
= disabled in it. But this ought to be a common enough general case?

-- 
Tom
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