Re: [PATCH v2] iio/adc: ingenic: fix (MIPS) ingenic-adc build errors

[Russell King (Oracle)]

On Fri, Nov 12, 2021 at 04:39:04PM -0800, Randy Dunlap wrote:
> On 11/12/21 9:29 AM, Jonathan Cameron wrote:
> > On Tue,  9 Nov 2021 18:37:55 -0800
> > Randy Dunlap <rdunlap@xxxxxxxxxxxxx> 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 <rdunlap@xxxxxxxxxxxxx>
> > > Reported-by: kernel test robot <lkp@xxxxxxxxx>
> > > Cc: Artur Rojek <contact@xxxxxxxxxxxxxx>
> > > Cc: Paul Cercueil <paul@xxxxxxxxxxxxxxx>
> > > Cc: linux-mips@xxxxxxxxxxxxxxx
> > > Cc: Jonathan Cameron <jic23@xxxxxxxxxx>
> > > Cc: Lars-Peter Clausen <lars@xxxxxxxxxx>
> > > Cc: linux-iio@xxxxxxxxxxxxxxx
> > > Cc: Florian Fainelli <f.fainelli@xxxxxxxxx>
> > > Cc: Andy Shevchenko <andy.shevchenko@xxxxxxxxx>
> > 
> > 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.
> 
> I'm all for that (above), but it's a mess.
> 
> > 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.
> 
> CONFIG_BCM63XX=y
> # CONFIG_MACH_INGENIC_SOC is not set
> CONFIG_INGENIC_ADC=y
> CONFIG_HAVE_CLK=y
> 
> 
> According to the build error messages (above), clk_get_parent()
> is missing. Looking at <linux/clk.h>, for CONFIG_HAVE_CLK=y,
> there is a prototype for clk_get_parent(), and if CONFIG_HAVE_CLK
> is not set, there is a stub for it.
> 
> Now look at drivers/clk/clk.c and drivers/clk/Makefile:
> 
> clk_get_parent() is defined in clk.c, which is built when
> CONFIG_COMMON_CLK=y, but that is not set in this .config file.
> 
> CONFIG_HAVE_CLK=y, but that doesn't get clk_get_parent()
> compiled.
> 
> So to me it is a disparity or incongruity between HAVE_CLK and COMMON_CLK.

HAVE_CLK means we have the clk API implemented. COMMON_CLK is one such
implementation, and HAVE_LEGACY_CLK is another group of implementations.

BCM63XX has its own implementation and uses HAVE_LEGACY_CLK, which can
be found in arch/mips/bcm63xx/clk.c.

If it doesn't support parent clocks, then it should provide a stub
clk_get_parent() that returns NULL at the very least.

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