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

[Randy Dunlap <rdunlap@infradead.org>]

On 11/13/21 12:34 AM, Russell King (Oracle) wrote:
> 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@infradead.org> 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@infradead.org>
>>>> Reported-by: kernel test robot <lkp@intel.com>
>>>> Cc: Artur Rojek <contact@artur-rojek.eu>
>>>> 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 <andy.shevchenko@gmail.com>
>>>
>>> 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.
> 

Russell- thanks for the explanation.
That works nicely.

Jonathan, I'll send a different patch.

-- 
~Randy