linux-kernel - Re: [PATCH v2 3/3] hwmon: pmbus: mpq8785: force direct mode for VID VOUT on MPQ8785/MPQ8786

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <07c39c3e-f82d-4ec0-b7fc-6ca9721d246d@roeck-us.net>
Date: Thu, 5 Feb 2026 08:58:37 -0800
From: Guenter Roeck <linux@...ck-us.net>
To: carl.lee@....com
Cc: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Charles Hsu <ythsu0511@...il.com>, linux-hwmon@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	peter.shen@....com, colin.huang2@....com
Subject: Re: [PATCH v2 3/3] hwmon: pmbus: mpq8785: force direct mode for VID
 VOUT on MPQ8785/MPQ8786

On Thu, Feb 05, 2026 at 06:01:39PM +0800, Carl Lee via B4 Relay wrote:
> From: Carl Lee <carl.lee@....com>
> 
> According to MPQ8785/MPQ8786 datasheet, VID mode configuration is
> the same as direct mode configuration. Therefore, when VOUT is
> reported in VID mode, it must be forced to use direct format.
> 

Why "must" ? Yes, the LSB is the same, at least for MPQ8785,
but that doesn't mean that the mode _must_ be overwritten. Maybe
I am missing it, but as far as I can see the datasheet doesn't
say that the VID mode configuration is the same as direct mode
configuration. It says that the _LSB_ is the same for both modes.

I _think_ the problem may be that the output voltages are not really
reported as VID values but as raw voltages, but the datasheet is a bit
vague in that regard. It talks about LSB values but doesn't exactly
say how voltages are reported, and for READ_VIN it is most definitely
wrong ("This bit is in VID mode with 25mv/LSB" doesn't make any sense).

Thanks,
Guenter

> Signed-off-by: Carl Lee <carl.lee@....com>
> ---
>  drivers/hwmon/pmbus/mpq8785.c | 20 ++++++++++++++++++++
>  1 file changed, 20 insertions(+)
> 
> diff --git a/drivers/hwmon/pmbus/mpq8785.c b/drivers/hwmon/pmbus/mpq8785.c
> index f35534836cb8..d6624af076c3 100644
> --- a/drivers/hwmon/pmbus/mpq8785.c
> +++ b/drivers/hwmon/pmbus/mpq8785.c
> @@ -48,6 +48,25 @@ static int mpq8785_identify(struct i2c_client *client,
>  	return 0;
>  };
>  
> +static int mpq8785_read_byte_data(struct i2c_client *client, int page, int reg)
> +{
> +	int ret;
> +
> +	switch (reg) {
> +	case PMBUS_VOUT_MODE:
> +		ret = pmbus_read_byte_data(client, page, reg);
> +		if (ret < 0)
> +			return ret;
> +
> +		if ((ret >> 5) == 1)
> +			return PB_VOUT_MODE_DIRECT;
> +	default:
> +		return -ENODATA;
> +	}
> +
> +	return ret;
> +}
> +
>  static int mpm82504_read_word_data(struct i2c_client *client, int page,
>  				   int phase, int reg)
>  {
> @@ -133,6 +152,7 @@ static int mpq8785_probe(struct i2c_client *client)
>  	case mpq8785:
>  	case mpq8786:
>  		info->identify = mpq8785_identify;
> +		info->read_byte_data = mpq8785_read_byte_data;
>  		break;
>  	default:
>  		return -ENODEV;
> 
> -- 
> 2.34.1
> 
>