-----Original Message-----
From: Guenter Roeck <redacted> On Behalf Of Guenter Roeck
Sent: Thursday, November 16, 2023 6:46 AM
To: Delphine_CC_Chiu/WYHQ/Wiwynn <Delphine_CC_Chiu@wiwynn.com>
Cc: patrick@stwcx.xyz; Jean Delvare <jdelvare@suse.com>; Jonathan Corbet
[off-list ref]; Rob Herring [off-list ref]; Krzysztof Kozlowski
[off-list ref]; Conor Dooley [off-list ref];
linux-i2c@vger.kernel.org; linux-hwmon@vger.kernel.org;
devicetree@vger.kernel.org; linux-kernel@vger.kernel.org;
linux-doc@vger.kernel.org
Subject: Re: [PATCH v2 2/2] hwmon: pmbus: Add ltc4286 driver

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On Wed, Nov 15, 2023 at 08:42:22AM +0000,
Delphine_CC_Chiu/WYHQ/Wiwynn wrote:

quoted

quoted

-----Original Message-----
From: Guenter Roeck <redacted> On Behalf Of Guenter Roeck
Sent: Tuesday, November 7, 2023 11:30 AM
To: Delphine_CC_Chiu/WYHQ/Wiwynn

[off-list ref];

quoted

quoted

patrick@stwcx.xyz; Jean Delvare [off-list ref]; Jonathan Corbet
[off-list ref]
Cc: Rob Herring <robh+dt@kernel.org>; Krzysztof Kozlowski
[off-list ref]; Conor Dooley
[off-list ref]; linux-i2c@vger.kernel.org;
linux-hwmon@vger.kernel.org; devicetree@vger.kernel.org;
linux-kernel@vger.kernel.org; linux-doc@vger.kernel.org
Subject: Re: [PATCH v2 2/2] hwmon: pmbus: Add ltc4286 driver

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On 11/6/23 19:08, Delphine_CC_Chiu/WYHQ/Wiwynn wrote:

quoted

quoted

-----Original Message-----
From: Guenter Roeck <redacted> On Behalf Of Guenter
Roeck
Sent: Tuesday, October 31, 2023 9:47 PM
To: Delphine_CC_Chiu/WYHQ/Wiwynn

[off-list ref];

quoted

quoted

quoted

quoted

patrick@stwcx.xyz; Jean Delvare [off-list ref]; Jonathan
Corbet [off-list ref]
Cc: Rob Herring <robh+dt@kernel.org>; Krzysztof Kozlowski
[off-list ref]; Conor Dooley
[off-list ref]; linux-i2c@vger.kernel.org;
linux-hwmon@vger.kernel.org; devicetree@vger.kernel.org;
linux-kernel@vger.kernel.org; linux-doc@vger.kernel.org
Subject: Re: [PATCH v2 2/2] hwmon: pmbus: Add ltc4286 driver

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On 10/30/23 23:46, Delphine_CC_Chiu/WYHQ/Wiwynn wrote:
[ ... ]

quoted

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+
+     ret = of_property_read_u32(client->dev.of_node,
+

"shunt-resistor-micro-ohms",

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&rsense);

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+     if (ret < 0)
+             return ret;
+
+     if (rsense == 0)
+             return -EINVAL;
+
+     info = &ltc4286_info;
+
+     /* Default of VRANGE_SELECT = 1, 102.4V */
+     if (device_property_read_bool(&client->dev,

"adi,vrange-select-25p6")) {

What if the adi,vrange-select-25p6 property is not provided,
but the chip is programmed for this range ?

The binding document tells programmers how to fill the dts.
Thus, programmers must fill this property if their system is
25.6 volts voltage

range.

quoted

Sure, but there is no else case, meaning VRANGE_SELECT is
unmodified in that case. There is no guarantee that the chip is in its

power-on state.

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The else case is in v2 ltc4286.c line 133 It means that the
voltage range for programmer is 102.4 volts which is default
value, so driver doesn't need to do any change for VRANGE_SELECT bit.

There is no guarantee that the value wasn't changed before the
driver was loaded.

We still can’t get your point.
Could you tell us about your concern here?

I have repeated it several times. You are making assumptions about register
values when the driver is loaded. Those asumptions are wrong since the state
of the chip is unknown when the driver is loaded. Any entty (BIOS, ROMMON,
i2cset, some operating system loaded earlier, or even some other driver or
platform code) may have changed those values.

On top of that, as I also have pointed out, LTC4287 supports saving its
configuration data in eeprom. That means that any chip configuration set
during production or anytime later will be retained, meaning any assumption
about chip configuration when the driver is loaded is even more wrong.

OK
We will check the register value first.
Then, we will check the property in dts.

Guenter