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Date:   Tue, 31 Jul 2018 08:01:17 +0100
From:   Lee Jones <lee.jones@linaro.org>
To:     Jae Hyun Yoo <jae.hyun.yoo@linux.intel.com>
Cc:     Rob Herring <robh+dt@kernel.org>, Jean Delvare <jdelvare@suse.com>,
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Subject: Re: [PATCH v7 08/12] mfd: intel-peci-client: Add PECI client MFD
 driver
Message-ID: <20180731070117.GE4662@dell>
References: <20180723214751.1733-1-jae.hyun.yoo@linux.intel.com>
 <20180723214751.1733-9-jae.hyun.yoo@linux.intel.com>
 <20180727082611.GE4628@dell>
 <acffdfef-cb20-4208-5297-d94bac5ecb1b@linux.intel.com>
 <CAL_JsqL7WkDOaegwmBDqLkRh0JfCo7O2krONVstjWMUsLiJMrg@mail.gmail.com>
 <7ab43253-1154-6e2f-b216-69b0d44b470a@linux.intel.com>
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On Mon, 30 Jul 2018, Jae Hyun Yoo wrote:

> Hi Rob,
> 
> On 7/30/2018 3:10 PM, Rob Herring wrote:
> > On Fri, Jul 27, 2018 at 11:36 AM Jae Hyun Yoo
> > <jae.hyun.yoo@linux.intel.com> wrote:
> > > 
> > > Hi Lee,
> > > 
> > > On 7/27/2018 1:26 AM, Lee Jones wrote:
> > > > On Mon, 23 Jul 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: Lee Jones <lee.jones@linaro.org>
> > > > > Cc: Rob Herring <robh+dt@kernel.org>
> > > > > 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                   |  14 ++
> > > > >    drivers/mfd/Makefile                  |   1 +
> > > > >    drivers/mfd/intel-peci-client.c       | 182 ++++++++++++++++++++++++++
> > > > >    include/linux/mfd/intel-peci-client.h |  81 ++++++++++++
> > > > >    4 files changed, 278 insertions(+)
> > > > >    create mode 100644 drivers/mfd/intel-peci-client.c
> > > > >    create mode 100644 include/linux/mfd/intel-peci-client.h
> > > > > 
> > > > > diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
> > > > > index f3fa516011ec..e38b591479d4 100644
> > > > > --- a/drivers/mfd/Kconfig
> > > > > +++ b/drivers/mfd/Kconfig
> > > > > @@ -595,6 +595,20 @@ config MFD_INTEL_MSIC
> > > > >         Passage) chip. This chip embeds audio, battery, GPIO, etc.
> > > > >         devices used in Intel Medfield platforms.
> > > > > 
> > > > > +config MFD_INTEL_PECI_CLIENT
> > > > > +    bool "Intel PECI client"
> > > > > +    depends on (PECI || COMPILE_TEST)
> > > > > +    select MFD_CORE
> > > > > +    help
> > > > > +      If you say yes to this option, support will be included for the
> > > > > +      multi-funtional Intel PECI (Platform Environment Control Interface)
> > > > > +      client. PECI is a one-wire bus interface that provides a communication
> > > > > +      channel from PECI clients in Intel processors and chipset components
> > > > > +      to external monitoring or control devices.
> > > > > +
> > > > > +      Additional drivers must be enabled in order to use the functionality
> > > > > +      of the device.
> > > > > +
> > > > >    config MFD_IPAQ_MICRO
> > > > >       bool "Atmel Micro ASIC (iPAQ h3100/h3600/h3700) Support"
> > > > >       depends on SA1100_H3100 || SA1100_H3600
> > > > > diff --git a/drivers/mfd/Makefile b/drivers/mfd/Makefile
> > > > > index 2852a6042ecf..29e2cacc58bd 100644
> > > > > --- a/drivers/mfd/Makefile
> > > > > +++ b/drivers/mfd/Makefile
> > > > > @@ -203,6 +203,7 @@ obj-$(CONFIG_MFD_INTEL_LPSS)     += intel-lpss.o
> > > > >    obj-$(CONFIG_MFD_INTEL_LPSS_PCI)   += intel-lpss-pci.o
> > > > >    obj-$(CONFIG_MFD_INTEL_LPSS_ACPI)  += intel-lpss-acpi.o
> > > > >    obj-$(CONFIG_MFD_INTEL_MSIC)       += intel_msic.o
> > > > > +obj-$(CONFIG_MFD_INTEL_PECI_CLIENT) += intel-peci-client.o
> > > > >    obj-$(CONFIG_MFD_PALMAS)   += palmas.o
> > > > >    obj-$(CONFIG_MFD_VIPERBOARD)    += viperboard.o
> > > > >    obj-$(CONFIG_MFD_RC5T583)  += rc5t583.o rc5t583-irq.o
> > > > > diff --git a/drivers/mfd/intel-peci-client.c b/drivers/mfd/intel-peci-client.c
> > > > > new file mode 100644
> > > > > index 000000000000..d7702cf1ea50
> > > > > --- /dev/null
> > > > > +++ b/drivers/mfd/intel-peci-client.c
> > > > > @@ -0,0 +1,182 @@
> > > > > +// SPDX-License-Identifier: GPL-2.0
> > > > > +// Copyright (c) 2018 Intel Corporation
> > > > > +
> > > > > +#include <linux/bitfield.h>
> > > > > +#include <linux/mfd/core.h>
> > > > > +#include <linux/mfd/intel-peci-client.h>
> > > > > +#include <linux/module.h>
> > > > > +#include <linux/peci.h>
> > > > > +#include <linux/of_device.h>
> > > > > +
> > > > > +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",
> > > > > +    },
> > > > > +};
> > > > 
> > > > The more I look at this driver, the less I think it fits into MFD.
> > > > 
> > > > What's stopping you from registering these devices directly from DT?
> > > > 
> > > 
> > > Because DT doesn't allow 2 nodes at the same address so Rob suggested
> > > MFD for this case.
> > 
> > Only after I first suggested you create cpu and dimm sensors from a
> > single hwmon driver. Perhaps you should figure out how to fix the
> > problem with delayed registration. Perhaps you can register the
> > sensor, but just delay returning actual data until it is ready.
> > 
> 
> The actual reason why I divided the single hwmon driver into two is for
> using recommended hwmon API set which doesn't allow incremental
> creation of sysfs attributes at run time - using of
> 'devm_hwmon_device_register_with_info' is suggested by Guenter instead
> of using other deprecated APIs.
> 
> The reason why the delayed registration is needed is, BMC kernel cannot
> know how many DIMM are installed in remote machine before the machine
> completing memory training and testing in POST. So dimm temp driver
> cannot create hwmon attributes in advance.
> 
> My thought is, this way is the best to address these requirements.

As I've previously explained, I do not think this is a good fit for
MFD.  Since this whole PECI piece is a bit, let's say 'niche', perhaps
it's better to contain the client within the PECI subsystem too.  You
can then use the platform_device_add() API to register devices as and
when required.

-- 
Lee Jones [李琼斯]
Linaro Services Technical Lead
Linaro.org │ Open source software for ARM SoCs
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