[U-Boot] Don't get any interrupts once I boot into Linux

[Benoît Thébaudeau]

Hi Fabio, Greg,

On Friday, September 14, 2012 5:15:17 PM, Fabio Estevam wrote:
> On Fri, Sep 14, 2012 at 12:04 PM, Greg Topmiller
> <Greg.Topmiller at jdsu.com> wrote:
> > I downloaded the V2012.07 version of u-boot from the git.denx.de
> > repository and built it for our target.  U-boot boots up properly
> > and I can use the commands but now when I boot into Linux I don't
> > seem to be getting interrupts.  The Linux kernel hangs in the
> > calculate_delay function waiting for ticks != jiffies.  I do not
> > get the interrupt for the timer.  I have verified that our
> > previous u-boot that is based on the 2009.12 version with
> > Freescale patches does work.  The timer interrupt occurs and
> > jiffies is incremented allowing the loop to exit.  Any help would
> > be appreciated.
> >
> 
> Which board are you using?

Same here with a custom i.MX51-based board and a FSL-based Linux. It works fine
with the FSL-based U-Boot (2009.12).

Some debugging has shown that:
 - The Linux timer is based on GPT.
 - The GPT counter runs fine at 8 Mincrements/s as expected.
 - The interrupt handler is never called.
 - The interrupt is based on output compare, but forcing the OC value a little
   bit after the counter value does not trigger the interrupt handler.
 - Resetting the GPT and clearing its registers prior to Linux timer init does
   not help.
 - There does not seem to be any wait or sleep modes involved.
 - In this loop, CPSR shows supervisor mode with FIQ disabled and IRQ enabled
   (same for both U-Boot versions).
 - This version of Linux does not set VBAR. Neither does the older U-Boot
   contrary to the latest, but setting VBAR to 0 like with the older U-Boot does
   not help.

The differences in system registers between these U-Boots are really small and
seem insignificant. The GPT clock source used by these versions is different,
but that should not be an issue with proper reinitialization in Linux.

The i.MX51 errata don't mention any issue like that, at least for GPT.
ENGcm09114 is similar, but in a very different context.

The next step is to dig into the interrupt controller settings and vectors to
check that Linux sets up everything properly. This issue is very likely caused
by this FSL Linux that unduly relies on the bootloader to initialize something.

Best regards,
Benoît