linux-kernel - Re: [PATCH v3 3/6] hwmon: (pmbus/core) add wp module param

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Message-ID: <1jjzdj5qyy.fsf@starbuckisacylon.baylibre.com>
Date: Mon, 04 Nov 2024 09:43:33 +0100
From: Jerome Brunet <jbrunet@...libre.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Jean Delvare <jdelvare@...e.com>,  Jonathan Corbet <corbet@....net>,
  Patrick Rudolph <patrick.rudolph@...ements.com>,  Naresh Solanki
 <naresh.solanki@...ements.com>,  Rob Herring <robh@...nel.org>,  Krzysztof
 Kozlowski <krzk+dt@...nel.org>,  Conor Dooley <conor+dt@...nel.org>,
  Delphine CC Chiu <Delphine_CC_Chiu@...ynn.com>,
  linux-hwmon@...r.kernel.org,  linux-kernel@...r.kernel.org,
  linux-doc@...r.kernel.org,  devicetree@...r.kernel.org,
  linux-i2c@...r.kernel.org
Subject: Re: [PATCH v3 3/6] hwmon: (pmbus/core) add wp module param

On Fri 01 Nov 2024 at 08:08, Guenter Roeck <linux@...ck-us.net> wrote:

> On Thu, Oct 24, 2024 at 08:10:37PM +0200, Jerome Brunet wrote:
>> Add a module parameter to force the write protection mode of pmbus chips.
>> 
>> 2 protections modes are provided to start with:
>> * 0: Remove the write protection if possible
>> * 1: Enable full write protection if possible
>> 
>> Of course, if the parameter is not provided, the default write protection
>> status of the pmbus chips is left untouched.
>> 
>> Suggested-by: Guenter Roeck <linux@...ck-us.net>
>> Signed-off-by: Jerome Brunet <jbrunet@...libre.com>
>> ---
>>  Documentation/admin-guide/kernel-parameters.txt |  4 ++
>>  drivers/hwmon/pmbus/pmbus_core.c                | 74 ++++++++++++++++++-------
>>  2 files changed, 59 insertions(+), 19 deletions(-)
>> 
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
>> index 1518343bbe2237f1d577df5656339d6224b769be..aa79242fe0a9238f618182289f18563ed63cba1c 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -4733,6 +4733,10 @@
>>  			Format: { parport<nr> | timid | 0 }
>>  			See also Documentation/admin-guide/parport.rst.
>>  
>> +	pmbus.wp=	[HW] PMBus Chips write protection forced mode
>> +			Format: { 0 | 1 }
>> +			See drivers/hwmon/pmbus/pmbus_core.c
>> +
>
> I have always seen that file as applicable for core kernel parameters,
> not for driver kernel parameters. I can not accept a global change like
> this without guidance. Please explain why it is desirable to have this
> parameter documented here and not in driver documentation.

No reason other than trying to document things the best I can.
Other subsystemw are documenting things in here too, I just did the same

See 'regulator_ignore_unused' for example.

I don't mind dropping this hunk if you prefer it that way.

>
>>  	pmtmr=		[X86] Manual setup of pmtmr I/O Port.
>>  			Override pmtimer IOPort with a hex value.
>>  			e.g. pmtmr=0x508
>> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
>> index 7bdd8f2ffcabc51500437182f411e9826cd7a55d..ce697ca03de01c0e5a352f8f6b72671137721868 100644
>> --- a/drivers/hwmon/pmbus/pmbus_core.c
>> +++ b/drivers/hwmon/pmbus/pmbus_core.c
>> @@ -31,6 +31,20 @@
>>  #define PMBUS_ATTR_ALLOC_SIZE	32
>>  #define PMBUS_NAME_SIZE		24
>>  
>> +/*
>> + * PMBus write protect forced mode:
>> + * PMBus may come up with a variety of write protection configuration.
>> + * 'pmbus_wp' may be used if a particular write protection is necessary.
>> + * The ability to actually alter the protection may also depend on the chip
>> + * so the actual runtime write protection configuration may differ from
>> + * the requested one. pmbus_core currently support the following value:
>> + * - 0: write protection removed
>> + * - 1: write protection fully enabled, including OPERATION and VOUT_COMMAND
>> + *      registers. Chips essentially become read-only with this.
>
> Would it be desirable to also suppport the ability to set the output voltage
> but not limits (PB_WP_VOUT) ?

I was starting simple, it is doable sure.
It is not something I will be able to test on actual since does not
support that.

Do you want me to add "2: write protection enable execpt for VOUT_COMMAND." ?

>
> Guenter

-- 
Jerome