Re: [PATCH v7 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

[Gary R Hook]

On 05/14/2018 12:50 PM, Randy Dunlap wrote:
> On 05/14/2018 10:20 AM, Gary R Hook wrote:
> > Implement a skeleton framework for debugfs support in the
> > AMD IOMMU.
> >
> > Signed-off-by: Gary R Hook <gary.hook@xxxxxxx>
> > ---
> >   drivers/iommu/Makefile            |    5 +++++
> >   drivers/iommu/amd_iommu_debugfs.c |   39 +++++++++++++++++++++++++++++++++++++
> >   drivers/iommu/amd_iommu_init.c    |    6 ++++--
> >   drivers/iommu/amd_iommu_proto.h   |    6 ++++++
> >   drivers/iommu/amd_iommu_types.h   |    3 +++
> >   5 files changed, 57 insertions(+), 2 deletions(-)
> >   create mode 100644 drivers/iommu/amd_iommu_debugfs.c
> >
> > diff --git a/drivers/iommu/Makefile b/drivers/iommu/Makefile
> > index 74cfbc392862..dd980f7dd8b6 100644
> > --- a/drivers/iommu/Makefile
> > +++ b/drivers/iommu/Makefile
> > @@ -30,3 +30,8 @@ obj-$(CONFIG_EXYNOS_IOMMU) += exynos-iommu.o
> >   obj-$(CONFIG_FSL_PAMU) += fsl_pamu.o fsl_pamu_domain.o
> >   obj-$(CONFIG_S390_IOMMU) += s390-iommu.o
> >   obj-$(CONFIG_QCOM_IOMMU) += qcom_iommu.o
> > +
> > +# This ensures that only the required files are compiled
> > +ifeq ($(CONFIG_IOMMU_DEBUGFS), y)
>
> Most Makefiles don't use a space before the 'y', but since you tested it,
> I guess either way works.

Pretty sure whitespace isn't used as a delimiter in this construct. I 
could be mistaken. But yes, it's perfectly serviceable.

> But why do this in the Makefile at all?  Why not just add another Kconfig
> symbol and simplify the Makefile?
>
> > +obj-$(CONFIG_AMD_IOMMU) += amd_iommu_debugfs.o
> > +endif


This was brought up a few weeks ago in, I believe, version 3 of this 
patch. That question was discussed (because that's what I did the first 
time out), and _someone_ _else_ asked about why I didn't just do it the 
way I've done it here.

Everyone has a preference.

I chose to simplify the choices and avoid multiple symbols, instead 
opting for two switches: choose your device, and decide on Debug FS 
enablement for it. IMO Very simple.

I can't fathom a scenario where this wouldn't work. Is there one?