Re: [PATCH] powerpc/time: use feature fixup in __USE_RTC() instead of cpu feature.

Benjamin Herrenschmidt [off-list ref] writes:

On Mon, 2019-08-26 at 21:41 +1000, Michael Ellerman wrote:

quoted

Christophe Leroy [off-list ref] writes:

quoted

sched_clock(), used by printk(), calls __USE_RTC() to know
whether to use realtime clock or timebase.

__USE_RTC() uses cpu_has_feature() which is initialised by
machine_init(). Before machine_init(), __USE_RTC() returns true,
leading to a program check exception on CPUs not having realtime
clock.

In order to be able to use printk() earlier, use feature fixup.
Feature fixups are applies in early_init(), enabling the use of
printk() earlier.

Signed-off-by: Christophe Leroy <redacted>
---
 arch/powerpc/include/asm/time.h | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

The other option would be just to make this a compile time decision, eg.
add CONFIG_PPC_601 and use that to gate whether we use RTC.

Given how many 601 users there are, maybe 1?, I think that would be a
simpler option and avoids complicating the code / binary for everyone
else.

Didn't we ditch 601 support years ago anyway ? We had workaround we
threw out I think...

Paul said his still booted recently.

cheers