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From:   Oleksandr Natalenko <oleksandr@natalenko.name>
To:     linux-hwmon@vger.kernel.org, Guenter Roeck <linux@roeck-us.net>,
        Jean Delvare <jdelvare@suse.com>,
        Zev Weiss <zev@bewilderbeest.net>
Cc:     openbmc@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        Renze Nicolai <renze@rnplus.nl>,
        Rob Herring <robh+dt@kernel.org>, devicetree@vger.kernel.org
Subject: Re: [PATCH 0/5] hwmon: (nct6775) Add i2c support
Date:   Sun, 27 Feb 2022 01:14:12 +0100
Message-ID: <2620147.mvXUDI8C0e@natalenko.name>
In-Reply-To: <20220226133047.6226-1-zev@bewilderbeest.net>
References: <20220226133047.6226-1-zev@bewilderbeest.net>
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Hello.

On sobota 26. =FAnora 2022 14:30:42 CET Zev Weiss wrote:
> Hello,
>=20
> This patch series augments the existing nct6775 driver with support
> for the hardware's i2c interface.

Is it something I can test on my ASUS Pro WS X570-ACE board as an ordinary =
user, and if so, how?

Thanks.

> Thus far the nct6775 driver has only supported the LPC interface,
> which is the main interface by which the Super-I/O chip is typically
> connected to the host (x86) processor.
>=20
> However, these chips also provide an i2c interface, which can provide
> a way for a BMC to also monitor sensor readings from them.  On some
> systems (such as the ASRock Rack ROMED8HM3 and X570-D4U) this may be
> the only way for the BMC to monitor host CPU temperatures (e.g. to
> indirectly access a TSI interface); this functionality is thus an
> important component of enabling OpenBMC to support such systems.
>=20
> In such an arrangement the Super-I/O chip is simultaneously controlled
> by two independent processors (the host and the BMC) which typically
> do not coordinate their accesses with each other.  In order to avoid
> conflicts between the two, the i2c driver avoids all writes to the
> device, since the BMC's needs with the hardware are merely that it be
> able to retrieve sensor readings.  This allows the host processor to
> remain ultimately in control of the chip and unaware of the BMC's use
> of it at all.
>=20
> The sole exception to the "no writes" rule for the i2c driver is for
> the bank-select register -- while I haven't been able to find any
> explicit statement in the Nuvoton datasheets guaranteeing this, all
> experiments I've done have indicated that, as one might hope, the i2c
> interface has its own bank-select register independent of the one used
> by the LPC interface.
>=20
> In terms of code structure, the approach taken in this series is to
> split the LPC-specific parts of the driver out into a separate module
> (called nct6775-platform), leaving the interface-independent parts in
> a generic driver (called nct6775-core).  The nct6775-i2c driver is
> then added as an additional consumer of the nct6775-core module's
> functionality.
>=20
> The first two patches make some relatively small infrastructural
> changes to the nct6775 driver; the bulk of the core/platform driver
> split is in the third patch.  The final two patches add DT bindings
> and the i2c driver itself.
>=20
> I've tested the nct6775-platform and nct6775-i2c drivers with the
> NCT6779D in an ASRock ROMED8HM3 system (the latter driver on its
> AST2500 BMC); both seem to work as expected.  Broader testing would of
> course be welcome though, as is review feedback.
>=20
>=20
> Thanks,
> Zev
>=20
>=20
> Zev Weiss (5):
>   hwmon: (nct6775) Rearrange attr-group initialization
>   hwmon: (nct6775) Add read-only mode
>   hwmon: (nct6775) Split core and platform driver
>   dt-bindings: hwmon: Add nuvoton,nct6775
>   hwmon: (nct6775) Add i2c driver
>=20
>  .../bindings/hwmon/nuvoton,nct6775.yaml       |   48 +
>  MAINTAINERS                                   |   12 +-
>  drivers/hwmon/Kconfig                         |   32 +-
>  drivers/hwmon/Makefile                        |    4 +-
>  drivers/hwmon/{nct6775.c =3D> nct6775-core.c}   | 1464 +----------------
>  drivers/hwmon/nct6775-i2c.c                   |  191 +++
>  drivers/hwmon/nct6775-platform.c              | 1185 +++++++++++++
>  drivers/hwmon/nct6775.h                       |  233 +++
>  8 files changed, 1763 insertions(+), 1406 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/hwmon/nuvoton,nct67=
75.yaml
>  rename drivers/hwmon/{nct6775.c =3D> nct6775-core.c} (75%)
>  create mode 100644 drivers/hwmon/nct6775-i2c.c
>  create mode 100644 drivers/hwmon/nct6775-platform.c
>  create mode 100644 drivers/hwmon/nct6775.h
>=20
>=20


=2D-=20
Oleksandr Natalenko (post-factum)