From: Andy Lutomirski <luto@amacapital.net>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Boaz Harrosh <boaz@plexistor.com>,
One Thousand Gnomes <gnomes@lxorguk.ukuu.org.uk>,
Rui Wang <ruiv.wang@gmail.com>, Jean Delvare <jdelvare@suse.de>,
Alun Evans <alun@badgerous.net>, Robert Elliott <Elliott@hp.com>,
"linux-i2c@vger.kernel.org" <linux-i2c@vger.kernel.org>,
Wolfram Sang <wsa@the-dreams.de>,
Mauro Carvalho Chehab <m.chehab@samsung.com>,
Paul Bolle <pebolle@tiscali.nl>, Tony Luck <tony.luck@intel.com>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 1/2] i2c_imc: New driver for Intel's iMC, found on LGA2011 chips
Date: Tue, 17 Mar 2015 13:14:43 -0700 [thread overview]
Message-ID: <CALCETrXvBxcZCyupHM6trb2Gv99MH9-HVG7ZuNGE2OPMZ7d7hA@mail.gmail.com> (raw)
In-Reply-To: <5503B59B.2020502@roeck-us.net>
On Mar 13, 2015 9:15 PM, "Guenter Roeck" <linux@roeck-us.net> wrote:
>
> On 03/09/2015 01:55 PM, Andy Lutomirski wrote:
>>
>> Sandy Bridge Xeon and Extreme chips have integrated memory
>> controllers with (rather limited) onboard SMBUS masters. This
>> driver gives access to the bus.
>>
>> There are various groups working on standardizing a way to arbitrate
>> access to the bus between the OS, SMM firmware, a BMC, hardware
>> thermal control, etc. In the mean time, running this driver is
>> unsafe except under special circumstances. Nonetheless, this driver
>> has real users.
>>
>> As a compromise, the driver will refuse to load unless
>> i2c_imc.allow_unsafe_access=Y. When safe access becomes available,
>> we can leave this option as a way for legacy users to run the
>> driver, and we'll allow the driver to load by default if safe bus
>> access is available.
>>
>> Signed-off-by: Andy Lutomirski <luto@amacapital.net>
>> ---
>> drivers/i2c/busses/Kconfig | 17 ++
>> drivers/i2c/busses/Makefile | 1 +
>> drivers/i2c/busses/i2c-imc.c | 567 +++++++++++++++++++++++++++++++++++++++++++
>> 3 files changed, 585 insertions(+)
>> create mode 100644 drivers/i2c/busses/i2c-imc.c
>>
>> diff --git a/drivers/i2c/busses/Kconfig b/drivers/i2c/busses/Kconfig
>> index ab838d9e28b6..50e3d79122dd 100644
>> --- a/drivers/i2c/busses/Kconfig
>> +++ b/drivers/i2c/busses/Kconfig
>> @@ -149,6 +149,23 @@ config I2C_ISMT
>> This driver can also be built as a module. If so, the module will be
>> called i2c-ismt.
>>
>> +config I2C_IMC
>> + tristate "Intel iMC (LGA 2011) SMBus Controller"
>> + depends on PCI && X86
>> + help
>> + If you say yes to this option, support will be included for the Intel
>> + Integrated Memory Controller SMBus host controller interface. This
>> + controller is found on LGA 2011 Xeons and Core i7 Extremes.
>> +
>> + There are currently no systems on which the kernel knows that it can
>> + safely enable this driver. For now, you need to pass this driver a
>> + scary module parameter, and you should only pass that parameter if you
>> + have a special motherboard and know exactly what you are doing.
>> + Special motherboards include the Supermicro X9DRH-iF-NV.
>> +
>
> I think the current approach of issuing warnings here and in the driver on load
> is the wrong one. For the most part, users will just run with distributions.
> If a distribution enables the driver, it will end up being used, warning or not.
>
> A much better approach, in my opinion, would be to only enable the driver for
> systems where it is known (or presumed) to be good, such as the Supermicro board
> mentioned above. This can be done with DMI data.
>
> For other boards, a 'force' module parameter can be added. This would ensure
> that the user _has_ to do something manually to load the driver. The warning
> on load would then only be displayed if the force module parameter is set.
>
This driver already has that: that's what "allow_unsafe_access" does.
I wouldn't be opposed to adding a DMI whitelist, although I really
don't want DMI entries to proliferate.
> Having said that, I am still not convinced that the driver should be in the kernel
> to start with. Browsing through Intel's datasheets, the registers are supported
> in E5-2600 v1, v2, and v3. However, in v3 Intel added a note saying that the registers
> should not be accessed by the OS directly, but only through the bios. Given that,
> and if that is possible, it might make more sense to rely on ACPI. It would then
> be up to the board and/or BIOS vendor to decide if the information should be available
> to the OS or not.
I think the plan is to add something to ACPI to tell us when we can
use these registers. Unfortunately I'm not privy to whatever the ACPI
committee is doing.
--Andy
next prev parent reply other threads:[~2015-03-17 20:15 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-09 20:55 [PATCH v2 0/2] i2c_imc: New driver, at long last Andy Lutomirski
2015-03-09 20:55 ` [PATCH v2 1/2] i2c_imc: New driver for Intel's iMC, found on LGA2011 chips Andy Lutomirski
2015-03-14 4:14 ` Guenter Roeck
2015-03-17 20:14 ` Andy Lutomirski [this message]
2015-06-17 13:18 ` Wolfram Sang
2015-06-17 15:12 ` Guenter Roeck
2015-03-09 20:55 ` [PATCH v2 2/2] i2c, i2c_imc: Add DIMM bus code Andy Lutomirski
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