[ptxdist] boot problem w/ barebox

[Uwe Kleine-König]

Hello,

On Mon, Sep 11, 2017 at 08:47:03PM +0200, Enrico Weigelt, metux IT consult wrote:
> On 11.09.2017 09:16, Uwe Kleine-König wrote:
> 
> > Try adding a #define DEBUG in linux-4.13/arch/arm/boot/compressed/head.S
> > > and make sure enabled DEBUG_LL and selected the right UART in your>
> .config.
> After deep digging in the init code, I've meanwhile fixed it (at least
> with self-compiled 2015 bbx - didn't try newer versions yet). In the end
> was just dt misconfiguration (that wasn't obvious in this dts wood,
> which I ported from the old 4.1-phy tree): the debug uart was disabled.
> 
> This lead to some funny situations:
> 
> * DEBUG_ll worked after fixing the port number (the counting is a bit
>   confusing: ttymxc1 is #2)

CONFIG_DEBUG_IMX_UART_PORT=2 means it should use UART-2 as documented in
the reference manual. But yeah, this is confusing, the problem is that
the hardware guy numbering the UARTS named the first UART UART-1 which
isn't what a kernel hacker would have picked.

> * console works up to the point where the uarts tty drivers are
>   configured. as the uart was disabled in dt, no tty driver was
>   associated (while ll driver was still active), so the clock was
>   disabled on some point, leading to supposedly hangup (actually,
>   just the console was gone)

When the UART tty driver are configured doesn't play a role here. At
some point during boot all unused clocks are disabled and up to then no
driver ensured your uart clock to be used. And maybe you had a real
hangup because writing to an UART with its clock off might have "funny"
effects.

> * hacking out the clock disable lead further to the point where rootfs
>   is mounted and init started

There is no need for a hack, just pass "clk_ignore_unused" on the kernel
command line.

Best regards
Uwe

-- 
Pengutronix e.K.                           | Uwe Kleine-König            |
Industrial Linux Solutions                 | http://www.pengutronix.de/  |