[U-Boot] [PATCH v2 3/4] tegra: Implement pre-console putc() for fdt warning

Wolfgang Denk wd at denx.de
Sat Mar 10 23:49:15 CET 2012

Dear Simon,

In message <CAPnjgZ1GzD3KJeaA1LLdYPQsoOLWJPxmX=FHFeUthkdPrUYt2g at mail.gmail.com> you wrote:
> > I think outputting data to all "potential" console ports is a really
> > bad thing, as you cannot know how your users are using the hardware.
> > They may have attached hardware to the UARTs, and the data you send to
> > the port causes a mis-function of the device. =A0I guess you don't add
> > to your documentation a warning like: select one port as console, and
> > leave allother ports unused, because we may send random date to all
> > ports any time?
> Only on a fatal error. Unfortunately this idea of 'fatal error' was
> lost in the conversion from board_panic_no_console() to

This "fatal error" might become a fatal accident in some cases if you
send random data to some port that controls some kind of machinery or
whatever.  Never ever do that!

> board_pre_console_putc(). I would be keen to move back to that
> original plan, so that the idea of a fatal error is captured. In a
> fatal error situation there is no prospect of the board working and
> the only hope is that we can alert the user.

Agreed.  But you must not do this by performing random actions on
random (potentially otherwise used [by the end user]) interfaces.

> > If you do not know which UART port to use, then the only consequence
> > can be not to use any UART prt at all.  Use a LED with blink codes or
> > whatever your hardwar ehas, but do not mess with random ports.
> I agres with the sentiment and this is a very ugly corner case, but in
> practice people want to know what happened, not just be presented with
> a brick.

Yes, I understand this.  But please try to find another way to signal
failure.  Do not perform random actions on a device - you could as
well always output all data on all UART ports because with this
codeyou cannot use the other ports for any serious purpose anyway.

> > I also cannot understand why you think you must init() and drain() the
> > UART for each character printed - ok, the latter is probably a
> > consequence of re-initializing the port for each character.
> > Eventually this will be not needed once you get rid of the re-init.
> OK so how about moving to a puts()-type interface? Then I can remove this.

Sorry, but I don't have enough context - pts() interface where or for

Best regards,

Wolfgang Denk

DENX Software Engineering GmbH,     MD: Wolfgang Denk & Detlev Zundel
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Phone: (+49)-8142-66989-10 Fax: (+49)-8142-66989-80 Email: wd at denx.de
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