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Subject: Re: [PATCH 0/5] Add uv_sysfs platform driver
To:     Justin Ernst <justin.ernst@hpe.com>,
        Borislav Petkov <bp@alien8.de>, Ingo Molnar <mingo@redhat.com>,
        Mark Gross <mgross@linux.intel.com>,
        Thomas Gleixner <tglx@linutronix.de>,
        Steve Wahl <steve.wahl@hpe.com>, x86@kernel.org
Cc:     Andy Shevchenko <andy@infradead.org>,
        Darren Hart <dvhart@infradead.org>,
        Dimitri Sivanich <dimitri.sivanich@hpe.com>,
        "H . Peter Anvin" <hpa@zytor.com>,
        Russ Anderson <russ.anderson@hpe.com>,
        linux-kernel@vger.kernel.org, platform-driver-x86@vger.kernel.org,
        Cezary Rojewski <cezary.rojewski@intel.com>,
        Ilya Dryomov <idryomov@gmail.com>,
        Jonathan Cameron <Jonathan.Cameron@huawei.com>,
        Mauro Carvalho Chehab <mchehab+huawei@kernel.org>,
        Vaibhav Jain <vaibhav@linux.ibm.com>
References: <20201117204224.51230-1-justin.ernst@hpe.com>
From:   Hans de Goede <hdegoede@redhat.com>
Message-ID: <99d26b0e-efd7-a32d-7be0-607c98ac2569@redhat.com>
Date:   Wed, 18 Nov 2020 12:00:49 +0100
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Hi,

On 11/17/20 9:42 PM, Justin Ernst wrote:
> Introduce a new platform driver to gather topology information from UV systems
> and expose that information via a sysfs interface at /sys/firmware/sgi_uv/.
> 
> Justin Ernst (5):
>   x86/platform/uv: Remove existing /sys/firmware/sgi_uv/ interface
>   x86/platform/uv: Add and export uv_bios_* functions
>   x86/platform/uv: Add new uv_sysfs platform driver
>   x86/platform/uv: Update ABI documentation of /sys/firmware/sgi_uv/
>   x86/platform/uv: Update MAINTAINERS for uv_sysfs driver

So patch 1/1 drops the existing 

/sys/firmware/sgi_uv/coherence_id
/sys/firmware/sgi_uv/partition_id

sysfs API, then according to patch 4/5 patch 3/5 reintroduces
the /sys/firmware/sgi_uv/partition_id API, but the /sys/firmware/sgi_uv/coherence_id
file is gone for ever ?

I'm not sure what userspace bits (may) depend on this but without more info
this looks like a clear violation of the do not break userspace APIs rule.

So, based on this, I have to nack this series in its current state.

Now if there is a strong believe there are 0 (not a few, but _zero_) users
out there who rely on the /sys/firmware/sgi_uv/coherence_id file then this
might be ok. But then there needs to be a technical analysis of why this is
ok in the commit message of the patch dropping this sysfs file.

Also the commit message of patch 1/5 should mention that
/sys/firmware/sgi_uv/partition_id will be re-introduced later through
another driver.

Regards,

Hans


> 
>  .../ABI/testing/sysfs-firmware-sgi_uv         | 137 ++-
>  MAINTAINERS                                   |   6 +
>  arch/x86/include/asm/uv/bios.h                |  49 +
>  arch/x86/include/asm/uv/uv_geo.h              | 103 +++
>  arch/x86/platform/uv/Makefile                 |   2 +-
>  arch/x86/platform/uv/bios_uv.c                |  54 ++
>  arch/x86/platform/uv/uv_sysfs.c               |  63 --
>  drivers/platform/x86/Kconfig                  |  11 +
>  drivers/platform/x86/Makefile                 |   3 +
>  drivers/platform/x86/uv_sysfs.c               | 853 ++++++++++++++++++
>  10 files changed, 1202 insertions(+), 79 deletions(-)
>  create mode 100644 arch/x86/include/asm/uv/uv_geo.h
>  delete mode 100644 arch/x86/platform/uv/uv_sysfs.c
>  create mode 100644 drivers/platform/x86/uv_sysfs.c
> 
> 
> base-commit: 4ef8451b332662d004df269d4cdeb7d9f31419b5
>