linux-kernel - RE: [PATCH v2 2/2] hwmon: pmbus: Add ltc4286 driver

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Message-ID: <SG2PR04MB55436CFA902895FD5472838AA1A9A@SG2PR04MB5543.apcprd04.prod.outlook.com>
Date:   Tue, 7 Nov 2023 03:08:48 +0000
From:   Delphine_CC_Chiu/WYHQ/Wiwynn <Delphine_CC_Chiu@...ynn.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Delphine_CC_Chiu/WYHQ/Wiwynn <Delphine_CC_Chiu@...ynn.com>,
        "patrick@...cx.xyz" <patrick@...cx.xyz>,
        Jean Delvare <jdelvare@...e.com>,
        Jonathan Corbet <corbet@....net>
CC:     Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Conor Dooley <conor+dt@...nel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "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>
Subject: RE: [PATCH v2 2/2] hwmon: pmbus: Add ltc4286 driver

> -----Original Message-----
> From: Guenter Roeck <groeck7@...il.com> On Behalf Of Guenter Roeck
> Sent: Tuesday, October 31, 2023 9:47 PM
> To: Delphine_CC_Chiu/WYHQ/Wiwynn <Delphine_CC_Chiu@...ynn.com>;
> patrick@...cx.xyz; Jean Delvare <jdelvare@...e.com>; Jonathan Corbet
> <corbet@....net>
> Cc: Rob Herring <robh+dt@...nel.org>; Krzysztof Kozlowski
> <krzysztof.kozlowski+dt@...aro.org>; Conor Dooley <conor+dt@...nel.org>;
> linux-i2c@...r.kernel.org; linux-hwmon@...r.kernel.org;
> devicetree@...r.kernel.org; linux-kernel@...r.kernel.org;
> linux-doc@...r.kernel.org
> Subject: Re: [PATCH v2 2/2] hwmon: pmbus: Add ltc4286 driver
> 
>   Security Reminder: Please be aware that this email is sent by an external
> sender.
> 
> On 10/30/23 23:46, Delphine_CC_Chiu/WYHQ/Wiwynn wrote:
> [ ... ]
> >>
> >>> +
> >>> +     ret = of_property_read_u32(client->dev.of_node,
> >>> +                                "shunt-resistor-micro-ohms",
> >> &rsense);
> >>> +     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.
> >
> 
> 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.

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.
Additionally, we have checked the behavior of VRANGE_SELECT bit with vendor.
Below is the reply from vendor:
[Our question]
If we change the VRANGE_SELECT bit value to 0, the value would return to default after we restart this device?
Or VRANGE_SELECT bit value would never change util someone change its value?
[ADI reply]
chip reset will go back to default. Thanks.

Thus, we must overwrite this bit if the user fill adi,vrange-select-25p6 here whenever driver probes

> 
> Guenter