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    SubjectRe: [PATCH 2/4] hwmon: Use subdir-ccflags-* to inherit debug flag
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    On 2021/2/6 4:08, Bjorn Helgaas wrote:
    > 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.

    i thought CONFIG_HWMON_DEBUG_CHIP=y means to enable debug including the
    subdirectories, so use subdir-ccflags-* will make sure the debug
    message on in the subdirectories, if there will be.

    please let me know if i understand wrong.

    Thanks,
    Yicong

    >
    > [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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