linux-kernel - Re: [PATCH 2/2] hwmon: pmbus: adm1275: add adm1281 support

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Message-ID: <1221f2fd-758e-4c10-8551-ed571fb1577f@roeck-us.net>
Date: Thu, 18 Apr 2024 04:55:00 -0700
From: Guenter Roeck <linux@...ck-us.net>
To: "SanBuenaventura, Jose" <Jose.SanBuenaventura@...log.com>
Cc: "linux-hwmon@...r.kernel.org" <linux-hwmon@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	"linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
	Jean Delvare <jdelvare@...e.com>, Rob Herring <robh@...nel.org>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Jonathan Corbet <corbet@....net>,
	Delphine CC Chiu <Delphine_CC_Chiu@...ynn.com>
Subject: Re: [PATCH 2/2] hwmon: pmbus: adm1275: add adm1281 support

On Thu, Apr 18, 2024 at 08:31:42AM +0000, SanBuenaventura, Jose wrote:
> 
> The lines mentioned were added initially because the STATUS_CML read capability
> seems to be only available in the adm1281 and so reading the said register with
> another device shouldn't be permitted.
  ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Why ? Sure, doing so causes the CML bit to be set, but the PMBus core uses
that method throughout to determine if a command/register is supported.
There are exceptions - some chips react badly if an attempt is made to read
unsupported registers. That is not the case for chips in this series, at
least not for the ones where I have evaluation boards. In such cases,
the chip driver should do nothing and let the PMBus core do its job.

> It seems though that the functionality is redundant and is already handled by 
> the PMBus core and maybe these lines can be removed and CML related errors
> can be checked using the status0 and status0_cml debugfs entries.

This has nothing to do with status0 and status0_cml debugfs entries. The
PMBUs core reads STATUS_CML if the CML status bit is set in the status
byte/word to determine if a command is supported or not. This is as
intended. There is nothing special to be done by a chip driver.

Thanks,
Guenter