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SubjectRe: [PATCH 2/4] hwmon: Use subdir-ccflags-* to inherit debug flag
On Fri, Feb 05, 2021 at 10:28:32AM -0800, Guenter Roeck wrote:
> On Fri, Feb 05, 2021 at 05:44:13PM +0800, Yicong Yang wrote:
> > From: Junhao He <hejunhao2@hisilicon.com>
> >
> > Use subdir-ccflags-* instead of ccflags-* to inherit the debug
> > settings from Kconfig when traversing subdirectories.
> >
> > Suggested-by: Bjorn Helgaas <bhelgaas@google.com>
> > Signed-off-by: Junhao He <hejunhao2@hisilicon.com>
> > Signed-off-by: Yicong Yang <yangyicong@hisilicon.com>
>
> What problem does this fix ? Maybe I am missing it, but I don't see
> DEBUG being used in a subdirectory of drivers/hwmon.

It's my fault for raising this question [1]. Yicong fixed a real
problem in drivers/pci, where we are currently using

ccflags-$(CONFIG_PCI_DEBUG) := -DDEBUG

so CONFIG_PCI_DEBUG=y turns on debug in drivers/pci, but not in the
subdirectories. That's surprising to users.

So my question was whether we should default to using subdir-ccflags
for -DDEBUG in general, and only use ccflags when we have
subdirectories that have their own debug options, e.g.,

drivers/i2c/Makefile:ccflags-$(CONFIG_I2C_DEBUG_CORE) := -DDEBUG
drivers/i2c/algos/Makefile:ccflags-$(CONFIG_I2C_DEBUG_ALGO) := -DDEBUG
drivers/i2c/busses/Makefile:ccflags-$(CONFIG_I2C_DEBUG_BUS) := -DDEBUG
drivers/i2c/muxes/Makefile:ccflags-$(CONFIG_I2C_DEBUG_BUS) := -DDEBUG

I mentioned drivers/hwmon along with a few others that have
subdirectories, do not have per-subdirectory debug options, and use
ccflags. I didn't try to determine whether those subdirectories
currently use -DDEBUG.

In the case of drivers/hwmon, several drivers do use pr_debug(),
and CONFIG_HWMON_DEBUG_CHIP=y turns those on. But if somebody
were to add pr_debug() to drivers/hwmon/occ/common.c, for example,
CONFIG_HWMON_DEBUG_CHIP=y would *not* turn it on. That sounds
surprising to me, but if that's what you intend, that's totally fine.

[1] https://lore.kernel.org/r/20210204161048.GA68790@bjorn-Precision-5520

> > ---
> > drivers/hwmon/Makefile | 2 +-
> > 1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/hwmon/Makefile b/drivers/hwmon/Makefile
> > index 09a86c5..1c0c089 100644
> > --- a/drivers/hwmon/Makefile
> > +++ b/drivers/hwmon/Makefile
> > @@ -201,5 +201,5 @@ obj-$(CONFIG_SENSORS_XGENE) += xgene-hwmon.o
> > obj-$(CONFIG_SENSORS_OCC) += occ/
> > obj-$(CONFIG_PMBUS) += pmbus/
> >
> > -ccflags-$(CONFIG_HWMON_DEBUG_CHIP) := -DDEBUG
> > +subdir-ccflags-$(CONFIG_HWMON_DEBUG_CHIP) := -DDEBUG
> >
> > --
> > 2.8.1
> >

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