Subject: Re: [PATCH v3] earlycon: 8250: Fix command line regression

From: Greg Kroah-Hartman <[email-masked]>
Date: Sat, 4 Apr 2015 18:52:17 +0200

On Sat, Apr 04, 2015 at 12:23:14PM -0400, Peter Hurley wrote:
> On 04/04/2015 12:09 PM, Greg Kroah-Hartman wrote:
> > On Sat, Apr 04, 2015 at 10:27:30AM -0400, Peter Hurley wrote:
> >> Restore undocumented behavior of kernel command line parameters of
> >> the forms:
> >>     console=uart[8250],io|mmio|mmio32,<addr>[,options]
> >>     console=uart[8250],<addr>[,options]
> >> where 'options' have not been specified; in this case, the hardware
> >> is assumed to be initialized.
> >>
> >> Document the required behavior of the original implementation.
> >>
> >> Fixes: c7cef0a84912cab3c9df8 ("console: Add extensible console matching")
> >> Reported-by: Yinghai Lu <[email-masked]>
> >> Signed-off-by: Peter Hurley <[email-masked]>
> >> ---
> >>
> >> v3: Fixed automatic console to port line settings initialization;
> >>     open-coded serial8250_console_setup() so the baud can be probed;
> >>     added sha reference in commit log
> >>
> >> v2: Fixed regression which allowed "console=uart1337,..." to start a
> >>     console (but not an earlycon)
> >>   + fixed earlycon= documentation related required behavior fixed by
> >>     this patch
> >>
> >>  Documentation/kernel-parameters.txt  | 18 ++++++++++++++---
> >>  drivers/tty/serial/8250/8250_core.c  | 38 +++++++++++++++++++++++++++++++++---
> >>  drivers/tty/serial/8250/8250_early.c | 19 ------------------
> >>  3 files changed, 50 insertions(+), 25 deletions(-)
> >>
> >> diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
> >> index bfcb1a6..1facf0b 100644
> >> --- a/Documentation/kernel-parameters.txt
> >> +++ b/Documentation/kernel-parameters.txt
> >> @@ -713,10 +713,18 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> >>  
> >>  		uart[8250],io,<addr>[,options]
> >>  		uart[8250],mmio,<addr>[,options]
> >> +		uart[8250],mmio32,<addr>[,options]
> >> +		uart[8250],0x<addr>[,options]
> >>  			Start an early, polled-mode console on the 8250/16550
> >>  			UART at the specified I/O port or MMIO address,
> >> -			switching to the matching ttyS device later.  The
> >> -			options are the same as for ttyS, above.
> >> +			switching to the matching ttyS device later.
> >> +			MMIO inter-register address stride is either 8-bit
> >> +			(mmio) or 32-bit (mmio32).
> >> +			If none of [io|mmio|mmio32], <addr> is assumed to be
> >> +			equivalent to 'mmio'. 'options' are specified in the
> >> +			same format described for ttyS above; if unspecified,
> >> +			the h/w is not re-initialized.
> >> +
> >>  		hvc<n>	Use the hypervisor console device <n>. This is for
> >>  			both Xen and PowerPC hypervisors.
> >>  
> >> @@ -944,11 +952,15 @@ bytes respectively. Such letter suffixes can also be entirely omitted.
> >>  		uart[8250],io,<addr>[,options]
> >>  		uart[8250],mmio,<addr>[,options]
> >>  		uart[8250],mmio32,<addr>[,options]
> >> +		uart[8250],0x<addr>[,options]
> >>  			Start an early, polled-mode console on the 8250/16550
> >>  			UART at the specified I/O port or MMIO address.
> >>  			MMIO inter-register address stride is either 8-bit
> >>  			(mmio) or 32-bit (mmio32).
> >> -			The options are the same as for ttyS, above.
> >> +			If none of [io|mmio|mmio32], <addr> is assumed to be
> >> +			equivalent to 'mmio'. 'options' are specified in the
> >> +			same format described for "console=ttyS<n>"; if
> >> +			unspecified, the h/w is not initialized.
> >>  
> >>  		pl011,<addr>
> >>  			Start an early, polled-mode console on a pl011 serial
> >> diff --git a/drivers/tty/serial/8250/8250_core.c b/drivers/tty/serial/8250/8250_core.c
> >> index e0fb5f0..f59c7a0 100644
> >> --- a/drivers/tty/serial/8250/8250_core.c
> >> +++ b/drivers/tty/serial/8250/8250_core.c
> >> @@ -3447,6 +3447,22 @@ static int univ8250_console_setup(struct console *co, char *options)
> >>  	return serial8250_console_setup(up, options);
> >>  }
> >>  
> >> +/* FIXME: this is broken on most other 8250 h/w */
> > 
> > What do you mean by "most other"?  What hardware does this work for?
> > What is it broken for?  What is someone supposed to think/do with this
> > comment?
> 
> It's a direct copy of the existing behavior for 8250 earlycon, which is
> broken for h/w with non-standard divisor registers. That's basically
> _every_ new design, because that's what vendors need to extend to support
> modern bitrates.
> 
> Affected h/w that I know of includes: 8250_dw, exar xr17v35 cards, omap8250,
> omap15xx, intel byt, intel mid.
> 
> But it was already broken for these and so not a regression.

Sorry, I know the function is a copy, you haven't broken anything that
wasn't already broken.  I see this comment as a "rant", but we might as
well turn that "rant" into something descriptive to let other people
know what is really going on here.

Sound reasonable?

thanks,

greg k-h