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

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Message-ID: <89a0e3af-8970-cd80-418d-630841795807@infradead.org>
Date:   Fri, 18 May 2018 09:49:12 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Gary R Hook <gary.hook@....com>, Joerg Roedel <joro@...tes.org>
Cc:     iommu@...ts.linux-foundation.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v7 2/2] iommu/amd: Add basic debugfs infrastructure for
 AMD IOMMU

On 05/18/2018 08:20 AM, Gary R Hook wrote:
> On 05/15/2018 08:46 AM, Joerg Roedel wrote:
>> On Mon, May 14, 2018 at 03:00:50PM -0500, Gary R Hook wrote:
>>> 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.
>>
>> You don't have this problem if you put the code in amd_iommu.c in an
>> IOMMU_DEBUGFS ifdef.
> 
> Of course. My preference, however, is a separate file to avoid size creep. That's why I've done it this way.
> 
> To whit: there have been threads discussing the advisability/acceptability of using #ifdefs for debug code. My take-away was to avoid them. Perhaps I misunderstood.
> 
> So: I don't understand your comment. Is this an observation, or is it an imperative statement? I'd like for a maintainer to clearly indicate what is acceptable, and I'll do it.
> 
> 

Hi,
I looked back at Robin Murphy's comments on April 17:

<quote>
Well, you could do a makefile-level dependency i.e.:

ifeq ($(CONFIG_IOMMU_DEBUG), y)
obj-$(CONFIG_AMD_IOMMU) += amd_iommu_debugfs.o
obj-$(CONFIG_BLAH_IOMMU) += blah_iommu_debugfs.o
...
endif

Or alternatively have an intermediate silent Kconfig option:

config AMD_IOMMU_DEBUG
	def_bool y
	depends on AMD_IOMMU && IOMMU_DEBUG

The makefile option is arguably ugly, but does at least scale better ;)
</quote>


I think the Kconfig option would have been the correct choice.

-- 
~Randy