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Date:   Thu, 10 Mar 2022 11:13:42 -0800
From:   Guenter Roeck <linux@roeck-us.net>
To:     Zev Weiss <zev@bewilderbeest.net>
Cc:     Jean Delvare <jdelvare@suse.com>, linux-hwmon@vger.kernel.org,
        Renze Nicolai <renze@rnplus.nl>,
        Oleksandr Natalenko <oleksandr@natalenko.name>,
        openbmc@lists.ozlabs.org, linux-kernel@vger.kernel.org,
        Rob Herring <robh+dt@kernel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>,
        devicetree@vger.kernel.org
Subject: Re: [PATCH v2 0/6] hwmon: (nct6775) Convert to regmap, add i2c
 support
Message-ID: <20220310191342.GB803893@roeck-us.net>
References: <20220309005047.5107-1-zev@bewilderbeest.net>
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In-Reply-To: <20220309005047.5107-1-zev@bewilderbeest.net>
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Hi,

On Tue, Mar 08, 2022 at 04:50:41PM -0800, Zev Weiss wrote:
> Hello,
> 
> This is v2 of my patches to add i2c support to the nct6775 driver.
> 

Just to let you know, I won't have time to review - much less test - the series 
before the commit window opens. Also, it is way too late for the upcoming release;
the changes are substantial enough to warrant a large soak time in linux-next.
The series will have to wait for v5.19.

Guenter

> Changes since v1 [0]:
>  - Added preparatory patch converting driver to regmap API [Guenter]
>  - Replaced ENOSPC with ENOBUFS and removed WARN_ON() in
>    nct6775_add_attr_group() [Guenter]
>  - Added dedicated symbol namespace [Guenter]
>  - Removed nct6775_write_temp() and nct6775_update_device() symbol
>    exports [Guenter]
>  - Reordered patches to put dt-bindings patch first [Krzysztof]
> 
> The nct6775-platform and nct6775-i2c drivers have both been tested on
> the NCT6779D in an ASRock ROMED8HM3 system and the NCT6798 [1] in an
> ASRock X570-D4U (the latter thanks to Renze, CCed); both seem to work
> as expected on both systems.  I don't have access to any asuswmi
> hardware, so testing of the nct6775-platform driver on that to ensure
> it doesn't break there would be appreciated (Oleksandr, perhaps?).
> 
> [0] https://lore.kernel.org/linux-hwmon/20220226133047.6226-1-zev@bewilderbeest.net/
> [1] Though it's physically labeled (mislabeled?) as an NCT6796, for
>     what that's worth.
> 
> A slightly edited version of the previous cover letter follows:
> 
> 
> This patch series augments the existing nct6775 driver with support
> for the hardware's i2c interface; along the way it converts the driver
> to use the regmap API, and splits the LPC-specific platform driver
> into a separate module from the interface-independent core.
> 
> 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.
> 
> 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.
> 
> 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.
> 
> 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,
> testing via manual register accesses (as detailed in [2]) has
> indicated that, as one might hope, the i2c interface has its own
> bank-select register independent of the one used by the LPC interface.
> 
> In terms of code structure, the approach taken in this series is to
> first convert the driver's register accesses to the regmap API, and
> then split the LPC-specific parts of it 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 (essentially just providing its own set of regmap
> read/write callback functions).
> 
> The first patch provides DT bindings for the nct6775, the second
> contains the change to convert all register accesses to use a regmap.
> The third and fourth patches make some relatively small
> infrastructural changes to the driver.  The core/platform driver split
> is in the fifth patch, and the final patch adds the i2c driver itself.
> 
> 
> Thanks,
> Zev
> 
> [2] https://lore.kernel.org/linux-hwmon/YhttzgDtGpcTniyw@hatter.bewilderbeest.net/
> 
> Zev Weiss (6):
>   dt-bindings: hwmon: Add nuvoton,nct6775
>   hwmon: (nct6775) Convert register access to regmap API
>   hwmon: (nct6775) Rearrange attr-group initialization
>   hwmon: (nct6775) Add read-only mode
>   hwmon: (nct6775) Split core and platform driver
>   hwmon: (nct6775) Add i2c driver
> 
>  .../bindings/hwmon/nuvoton,nct6775.yaml       |   48 +
>  MAINTAINERS                                   |   12 +-
>  drivers/hwmon/Kconfig                         |   32 +-
>  drivers/hwmon/Makefile                        |    4 +-
>  drivers/hwmon/{nct6775.c => nct6775-core.c}   | 2310 +++++------------
>  drivers/hwmon/nct6775-i2c.c                   |  179 ++
>  drivers/hwmon/nct6775-platform.c              | 1232 +++++++++
>  drivers/hwmon/nct6775.h                       |  252 ++
>  8 files changed, 2382 insertions(+), 1687 deletions(-)
>  create mode 100644 Documentation/devicetree/bindings/hwmon/nuvoton,nct6775.yaml
>  rename drivers/hwmon/{nct6775.c => nct6775-core.c} (69%)
>  create mode 100644 drivers/hwmon/nct6775-i2c.c
>  create mode 100644 drivers/hwmon/nct6775-platform.c
>  create mode 100644 drivers/hwmon/nct6775.h
> 
> -- 
> 2.35.1
>