Re: [PATCH] PCI: Use subdir-ccflags-* to inherit debug flag

[Bjorn Helgaas]

[+cc Masahiro, Michal, linux-kbuild, linux-kernel]

On Thu, Feb 04, 2021 at 07:30:15PM +0800, Yicong Yang wrote:
> From: Junhao He <hejunhao2@xxxxxxxxxxxxx>
> 
> Use subdir-ccflags-* instead of ccflags-* to inherit the debug
> settings from Kconfig when traversing subdirectories.

So I guess the current behavior is:

  If CONFIG_PCI_DEBUG=y, add -DDEBUG to CFLAGS in the current
  directory, but not in any subdirectories

and the behavior after this patch is:

  If CONFIG_PCI_DEBUG=y, add -DDEBUG to CFLAGS in the current
  directory and any subdirectories

Is that right?  That makes sense to me.  I wonder if any other places
have this issue?

'git grep "^ccflags.*-DDEBUG"' finds a few cases where subdirectories
use their own debug config 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

But some have subdirectories that look like they probably should be
included by using subdir-ccflags, e.g.,

  drivers/base/Makefile:ccflags-$(CONFIG_DEBUG_DRIVER) := -DDEBUG
  drivers/base/power/Makefile:ccflags-$(CONFIG_DEBUG_DRIVER) := -DDEBUG
    # drivers/base/{firmware_loader,regmap,test}/ not included

  drivers/hwmon/Makefile:ccflags-$(CONFIG_HWMON_DEBUG_CHIP) := -DDEBUG
    # drivers/hwmon/{occ,pmbus}/ not included

  drivers/pps/Makefile:ccflags-$(CONFIG_PPS_DEBUG) := -DDEBUG
  drivers/pps/clients/Makefile:ccflags-$(CONFIG_PPS_DEBUG) := -DDEBUG
    # drivers/pps/generators/ not included

There are many more places that add -DDEBUG to ccflags-y that *don't*
have subdirectories.

I wonder the default should be that we use subdir-ccflags all the
time, and use ccflags only when we actually want different
CONFIG_*_DEBUG options for subdirectories.

> Signed-off-by: Junhao He <hejunhao2@xxxxxxxxxxxxx>
> Signed-off-by: Yicong Yang <yangyicong@xxxxxxxxxxxxx>
> ---
>  drivers/pci/Makefile | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/Makefile b/drivers/pci/Makefile
> index 11cc794..d62c4ac 100644
> --- a/drivers/pci/Makefile
> +++ b/drivers/pci/Makefile
> @@ -36,4 +36,4 @@ obj-$(CONFIG_PCI_ENDPOINT)	+= endpoint/
>  obj-y				+= controller/
>  obj-y				+= switch/
>  
> -ccflags-$(CONFIG_PCI_DEBUG) := -DDEBUG
> +subdir-ccflags-$(CONFIG_PCI_DEBUG) := -DDEBUG
> -- 
> 2.8.1
>