On Tue,  9 Nov 2021 18:37:55 -0800
Randy Dunlap [off-list ref] wrote:

MIPS does not always provide clk*() interfaces and there are no
always-present stubs for them, so depending on "MIPS || COMPILE_TEST"
is not strong enough to prevent build errors.

Likewise MACH_INGENIC_SOC || COMPILE_TEST is not strong enough
since if only COMPILE_TEST=y (with some other MIPS MACH_ or CPU or
BOARD setting), there are still the same build errors.

It looks like depending on MACH_INGENIC is the only thing that is
sufficient here in order to prevent build errors.

mips-linux-ld: drivers/iio/adc/ingenic-adc.o: in function `jz4770_adc_init_clk_div':
ingenic-adc.c:(.text+0xe4): undefined reference to `clk_get_parent'
mips-linux-ld: drivers/iio/adc/ingenic-adc.o: in function `jz4725b_adc_init_clk_div':
ingenic-adc.c:(.text+0x1b8): undefined reference to `clk_get_parent'

Fixes: 1a78daea107d ("IIO: add Ingenic JZ47xx ADC driver.")
Signed-off-by: Randy Dunlap <redacted>
Reported-by: kernel test robot <redacted>
Cc: Artur Rojek <redacted>
Cc: Paul Cercueil <paul@crapouillou.net>
Cc: linux-mips@vger.kernel.org
Cc: Jonathan Cameron <jic23@kernel.org>
Cc: Lars-Peter Clausen <lars@metafoo.de>
Cc: linux-iio@vger.kernel.org
Cc: Florian Fainelli <f.fainelli@gmail.com>
Cc: Andy Shevchenko <redacted>

I'm a bit confused.  There are stubs in include/linux/clk.h for these.
Why do those not apply here? Are these platforms built with CONFIG_CLK but
don't provide all the functions?

That sounds highly error prone and rather defeats the object of the
stubs.  Could we either provide the missing stubs, or solve this some other
way.  I'm not keen to massively cut the build coverage this driver is getting
by dropping COMPILE_TEST if there is any route to avoid doing so.

Based on the guess than any platform with clks must be able to turn them on
I grepped for int clk_enable() and there seem to be only two possiblities
bcm63xx and lantiq as sources of the build breakage.

Jonathan