linux-kernel - Re: [PATCH v8 2/2] iommu/amd: Add basic debugfs infrastructure for AMD IOMMU

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Date:   Mon, 4 Jun 2018 18:23:40 -0700
From:   Randy Dunlap <rdunlap@...radead.org>
To:     Greg KH <greg@...ah.com>, Gary R Hook <gary.hook@....com>
Cc:     iommu@...ts.linux-foundation.org, joro@...tes.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v8 2/2] iommu/amd: Add basic debugfs infrastructure for
 AMD IOMMU

On 05/29/2018 11:39 AM, Greg KH wrote:
> On Tue, May 29, 2018 at 01:23:23PM -0500, Gary R Hook wrote:
>> Implement a skeleton framework for debugfs support in the
>> AMD IOMMU. Add a hidden boolean to Kconfig that is defined
>> for the AMD IOMMU when general IOMMY DebugFS support is
>> enabled.
>>
>> Signed-off-by: Gary R Hook <gary.hook@....com>
>> ---
>>  drivers/iommu/Kconfig             |    4 ++++
>>  drivers/iommu/Makefile            |    1 +
>>  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   |    5 +++++
>>  6 files changed, 59 insertions(+), 2 deletions(-)
>>  create mode 100644 drivers/iommu/amd_iommu_debugfs.c
>>
>> diff --git a/drivers/iommu/Kconfig b/drivers/iommu/Kconfig
>> index f9af25ac409f..ec223f6f4ad4 100644
>> --- a/drivers/iommu/Kconfig
>> +++ b/drivers/iommu/Kconfig
>> @@ -137,6 +137,10 @@ config AMD_IOMMU
>>  	  your BIOS for an option to enable it or if you have an IVRS ACPI
>>  	  table.
>>  
>> +config AMD_IOMMU_DEBUGFS
>> +	def_bool y
> 
> Why default y?  Can you not boot a box without this?  If not, it should
> not be Y.
> 
>> +	depends on AMD_IOMMU && IOMMU_DEBUGFS
>> +
>>  config AMD_IOMMU_V2
>>  	tristate "AMD IOMMU Version 2 driver"
>>  	depends on AMD_IOMMU

Gary,

By far, most driver-debugfs additions are optional and include a user Kconfig prompt
so that user's can choose whether to enable it or not.

I suggest that the way forward is to fix Greg's debugfs_() api comments
and to add a prompt string to AMD_IOMMU_DEBUGFS.


-- 
~Randy