linux-kernel - Re: [PATCH 2/4] hwmon: Use subdir-ccflags-* to inherit debug flag

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Date:   Mon, 8 Feb 2021 18:51:57 +0800
From:   Yicong Yang <yangyicong@...ilicon.com>
To:     Bjorn Helgaas <helgaas@...nel.org>,
        Guenter Roeck <linux@...ck-us.net>
CC:     <gregkh@...uxfoundation.org>, <jdelvare@...e.com>,
        <giometti@...eenne.com>, <abbotti@....co.uk>,
        <hsweeten@...ionengravers.com>, <kw@...ux.com>,
        <linux-kernel@...r.kernel.org>, <linux-pm@...r.kernel.org>,
        <linux-hwmon@...r.kernel.org>, <devel@...verdev.osuosl.org>,
        <linux-kbuild@...r.kernel.org>, <masahiroy@...nel.org>,
        <michal.lkml@...kovi.net>, <prime.zeng@...wei.com>,
        <linuxarm@...neuler.org>
Subject: Re: [PATCH 2/4] hwmon: Use subdir-ccflags-* to inherit debug flag

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@...ilicon.com>
>>>
>>> Use subdir-ccflags-* instead of ccflags-* to inherit the debug
>>> settings from Kconfig when traversing subdirectories.
>>>
>>> Suggested-by: Bjorn Helgaas <bhelgaas@...gle.com>
>>> Signed-off-by: Junhao He <hejunhao2@...ilicon.com>
>>> Signed-off-by: Yicong Yang <yangyicong@...ilicon.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
>>>
> 
> .
>