linux-kernel - Re: [PATCH v2 7/7] x86/boot: Support nocfg parameter for earlyprintk

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Message-ID: <20190328140039.GC9224@smile.fi.intel.com>
Date:   Thu, 28 Mar 2019 16:00:39 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Borislav Petkov <bp@...en8.de>
Cc:     "H. Peter Anvin" <hpa@...or.com>, x86@...nel.org,
        Thomas Gleixner <tglx@...utronix.de>,
        Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 7/7] x86/boot: Support nocfg parameter for earlyprintk

On Thu, Mar 28, 2019 at 02:42:13PM +0100, Borislav Petkov wrote:
> On Thu, Mar 28, 2019 at 03:21:53PM +0200, Andy Shevchenko wrote:
> > If the connection to the target is done via serial interface and
> > firmware and / or bootloader already did necessary configuration.
> 
> Again: how is the user supposed to know that?

How one knows that she is typing on keyboard right now and not on touch screen?
I really don't get this. User either knows this beforehand or doesn't care.
Maybe she needs to read documentation on hardware at some point?

> When a user sees "nocfg"'s
> documentation, how is the user supposed to decide whether she needs
> to supply nocfg or not?

The problem nocfg tries to solve is a hard coded default baud rate and
impossibility to know at this stage all parameters of the serial interface.

> Which exact setups will need to supply nocfg on the cmdline?

If it's _non-standard_ serial interface (by meaning of I/O accessors and port
addresses), user may consider to use this options in case the interface to
communicate with kernel is serial one and its configuration is done by other
means (firmware / bootloader / EFI / etc).

-- 
With Best Regards,
Andy Shevchenko