Message-Id: <20140731032527.D2C5AC40A02@trevor.secretlab.ca>
Date:	Wed, 30 Jul 2014 21:25:27 -0600
From:	Grant Likely <grant.likely@...retlab.ca>
To:	Rob Herring <robherring2@...il.com>
Cc:	Vineet Gupta <Vineet.Gupta1@...opsys.com>,
	linux-next <linux-next@...r.kernel.org>,
	Anton Kolesov <Anton.Kolesov@...opsys.com>,
	lkml <linux-kernel@...r.kernel.org>,
	greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	"linux-serial@...r.kernel.org" <linux-serial@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: ARC fails to boot on linux-next of 20140711

On Sat, 26 Jul 2014 15:10:28 -0500, Rob Herring <robherring2@...il.com> wrote:
> On Sat, Jul 26, 2014 at 11:50 AM, Grant Likely
> <grant.likely@...retlab.ca> wrote:
> > On Sat, 26 Jul 2014 06:52:36 +0000, Vineet Gupta <Vineet.Gupta1@...opsys.com> wrote:
> >> Hi Rob,
> >>
> >> On Friday 25 July 2014 07:45 PM, Rob Herring wrote:
> >> > On Fri, Jul 25, 2014 at 6:02 AM, Vineet Gupta
> >> > <Vineet.Gupta1@...opsys.com> wrote:
> >> >> > Hi Grant,
> >> >> >
> >> >> > linux-next has a series for arc_uart (via tty tree) which converts it to generic
> >> >> > earlycon and specifies console via /chosen/stdout-path vs.  an explicit param in
> >> >> > /chose/bootargs
> >> >> >
> >> >> > 2014-06-24 9da433c0a0b5 ARC: [arcfpga] stdout-path now suffices for earlycon/console
> >> >> >
> >> >> > This relied on prev commit of yours (from linux next of 20140711), which seem to
> >> >> > have disappeared now.
> >> >> >
> >> >> > 2014-03-27 a9296cf2d0b6 of: Create of_console_check() for selecting a console
> >> >> > specified in /chosen
> >> >> > 2014-03-27 cfa9cacc5dd3 of: Enable console on serial ports specified by
> >> >> > /chosen/stdout-path
> >> >> >
> >> >> > Is there a specific reason for dropping these patches (or perhaps a merge to be
> >> >> > merged). I cherry-picked both but still doesn't work.
> >> >> >
> >> >> > Can you please advise next step forward, before I go off debugging with those
> >> >> > patches in.
> >> > There's an issue that if you have stdout-path and "earlycon" on the
> >> > command line, the kernel will switch to tty0 and disable the earlycon.
> >> >
> >> > This is the "fix", but I don't like adding the DT dependency into generic code:
> >> >
> >> > @@ -2382,7 +2386,7 @@ void register_console(struct console *newcon)
> >> >                 if (newcon->setup == NULL ||
> >> >                     newcon->setup(newcon, NULL) == 0) {
> >> >                         newcon->flags |= CON_ENABLED;
> >> > -                       if (newcon->device) {
> >> > +                       if (newcon->device  && !of_stdout) {
> >> >                                 newcon->flags |= CON_CONSDEV;
> >> >                                 preferred_console = 0;
> >> >                         }
> >>
> >> The DT settings relevant for ARC, which enable generic-earlycon and
> >> console-with-stdout-path are as follows
> >>
> >>         chosen {
> >>                 bootargs = "earlycon";
> >>                 stdout-path = &arcuart0;
> >>         };
> >>
> >> ....
> >>                 arcuart0: serial@...c1000 {
> >>                         compatible = "snps,arc-uart";
> >>
> >> And it works w/o above hunk, provided the 2 patches from Grant exist in linux-next
> >> which they don't at the moment. I'm pretty confused how the hunk above comes into
> >> picture.
> >>
> >> And if not then I will have to get the ARC std-out patch reverted in tty-next as
> >> it is broken.
> >
> > You need to revert it anyway, the dependency chain is broken. Just
> > because something is in linux-next doesn't mean it will be merged.
> > Dependencies must always be in the branch to which you commit.
> >
> > If that doesn't happen (like here) then bisecting is broken and the
> > dependencies may not actually get merged.
> >
> > When this happens, what you're supposed to do is tell the maintainers
> > what commits the patch depends on so that it can be applied to the
> > correct tree. In this case I could take it through my devicetree branch
> > that contains the console patches.
> >
> > If a patch depends on commits in several branches then it is a bit more
> > complex. What we usually do is create a new branch that merges in each
> > branch that is depended on, and then apply the commit on top of that.
> >
> > As for the console patches, I'm only going to be putting them back if I
> > can devise a good fix for the earlycon duplication issue.
> 
> There is also a simple work-around. You have to specify the console
> when you use earlycon. For example, you can add "earlycon
> console=ttyAMA0" instead of just earlycon. To summarize, this is the
> state of combinations of console params:
> 
> Working:
> stdout-path
> console=blah
> stdout-path + console=blah
> earlycon=blah
> 
> Not working:
> stdout-path + earlycon
> 
> Also, it is a developer only feature which is new. You will be aware
> of an issue because the earlycon starts output and then stops on
> switching to tty0 versus complete silence which could be anything.

Fair enough. Okay, I'm going to put it back into linux-next. The proper
fix can come later.

> There are other landmines in this area already. For example, setting
> earlycon on ARM will break the boot because an ioremap is attempted
> before paging_init. This is nothing new, but has always been the case
> if the 8250 driver was enabled.

We should not allow earlycon to be selectable on ARM until this is
fixed. Can you do a patch for this?

g.
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