Re: [PATCH linux-next v5 08/13] drivers/mfd: Add PECI client mfd driver

[Lee Jones <lee.jones@linaro.org>]

On Mon, 18 Jun 2018, Jae Hyun Yoo wrote:

> On 6/17/2018 10:59 PM, Lee Jones wrote:
> > On Thu, 14 Jun 2018, Jae Hyun Yoo wrote:
> > 
> > > Thanks for the review. Please see my inline answers.
> > > 
> > > On 6/12/2018 11:30 PM, Lee Jones wrote:
> > > > On Fri, 01 Jun 2018, Jae Hyun Yoo wrote:
> > > > 
> > > > > This commit adds PECI client mfd driver.
> > > > > 
> > > > > Signed-off-by: Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
> > > > > Cc: Andrew Jeffery <andrew@aj.id.au>
> > > > > Cc: James Feist <james.feist@linux.intel.com>
> > > > > Cc: Jason M Biils <jason.m.bills@linux.intel.com>
> > > > > Cc: Joel Stanley <joel@jms.id.au>
> > > > > Cc: Vernon Mauery <vernon.mauery@linux.intel.com>
> > > > > ---
> > > > >    drivers/mfd/Kconfig             |  11 ++
> > > > >    drivers/mfd/Makefile            |   1 +
> > > > >    drivers/mfd/peci-client.c       | 205 ++++++++++++++++++++++++++++++++
> > > > >    include/linux/mfd/peci-client.h |  60 ++++++++++
> > > > >    4 files changed, 277 insertions(+)
> > > > >    create mode 100644 drivers/mfd/peci-client.c
> > > > >    create mode 100644 include/linux/mfd/peci-client.h

[...]

> > > > > +/**
> > > > > + * Architectures other than x86 cannot include the header file so define these
> > > > > + * at here. These are needed for detecting type of client x86 CPUs behind a PECI
> > > > > + * connection.
> > > > > + */
> > > > > +#define INTEL_FAM6_HASWELL_X   0x3F
> > > > > +#define INTEL_FAM6_BROADWELL_X 0x4F
> > > > > +#define INTEL_FAM6_SKYLAKE_X   0x55
> > > > > +#endif
> > > > > +
> > > > > +#define LOWER_NIBBLE_MASK      GENMASK(3, 0)
> > > > > +#define UPPER_NIBBLE_MASK      GENMASK(7, 4)
> > > > > +
> > > > > +#define CPU_ID_MODEL_MASK      GENMASK(7, 4)
> > > > > +#define CPU_ID_FAMILY_MASK     GENMASK(11, 8)
> > > > > +#define CPU_ID_EXT_MODEL_MASK  GENMASK(19, 16)
> > > > > +#define CPU_ID_EXT_FAMILY_MASK GENMASK(27, 20)
> > > > 
> > > > In the case of X86 based devices, are these being redefined?
> > > > 
> > > 
> > > No define even in x86 arch build. These masks just for PECI use cases.
> > > Also, the CPUs in this implementation is not for local CPUs, but for
> > > remote CPUs which are connected through PECI interface. It also means
> > > that this code can be running on non-x86 kernel too.
> > 
> > This is starting to sound like a 'remoteproc' driver, no?
> 
> This is driver for remote Intel CPUs that are behind in PECI connection.

Sounds like 'remoteproc' to me.

> > > > > +enum cpu_gens {
> > > > > +	CPU_GEN_HSX = 0, /* Haswell Xeon */
> > > > > +	CPU_GEN_BRX,     /* Broadwell Xeon */
> > > > > +	CPU_GEN_SKX,     /* Skylake Xeon */
> > > > > +};
> > > > > +
> > > > > +static struct mfd_cell peci_functions[] = {
> > > > > +	{
> > > > > +		.name = "peci-cputemp",
> > > > > +		.of_compatible = "intel,peci-cputemp",
> > > > > +	},
> > > > > +	{
> > > > > +		.name = "peci-dimmtemp",
> > > > > +		.of_compatible = "intel,peci-dimmtemp",
> > > > > +	},
> > > > > +};
> > > > 
> > > > A couple of temp sensors?  This isn't looking very MFD-like.
> > > > 
> > > > What makes this an MFD?
> > > > 
> > > 
> > > Currently it has only a couple of temp sensors but it's just one of
> > > PECI function. Other PECI functions will be added later so it's the
> > > reason why it should be an MFD. Please see the following PECI sideband
> > > functions that I introduced in the cover letter of this patch set.
> > > 
> > > * Processor and DRAM thermal management
> > > * Platform Manageability
> > > * Processor Interface Tuning and Diagnostics
> > > * Failure Analysis
> > 
> > Are these all devices in their own right?
> > 
> > Will they each have drivers associated with them?
> > 
> > Is there a datasheet for this PECI device?
> > 
> 
> Temperature monitoring driver which I'm trying to upstream should be
> added into hwmon subsystem, but other function drivers should be added
> as a platform driver or as a something else, so it is the reason why I
> made this MFD driver because these function drivers are separated but
> use the same device - the remote CPU - actually. Datasheet is available
> through http://www.intel.com/design/literature.htm with an NDA process.
> Intel is providing the datasheet to HW vendors.

I logged in an searched for "PECI".  These were my results:

  https://i.imgur.com/y86S96I.png

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
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