linux-kernel - Re: [PATCH v5 4/4] misc: tps6594-pfsm: Add driver for TI TPS6594 PFSM

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Date:   Thu, 30 Mar 2023 17:45:44 +0200
From:   Julien Panis <jpanis@...libre.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     lee@...nel.org, robh+dt@...nel.org,
        krzysztof.kozlowski+dt@...aro.org, corbet@....net, arnd@...db.de,
        derek.kiernan@...inx.com, dragan.cvetic@...inx.com,
        yi.l.liu@...el.com, jgg@...pe.ca, razor@...ckwall.org,
        stephen@...workplumber.org, prabhakar.csengg@...il.com,
        contact@...rsion.fr, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-doc@...r.kernel.org,
        sterzik@...com, u-kumar1@...com, eblanc@...libre.com,
        jneanne@...libre.com
Subject: Re: [PATCH v5 4/4] misc: tps6594-pfsm: Add driver for TI TPS6594 PFSM



On 3/30/23 10:35, Greg KH wrote:
> On Thu, Mar 30, 2023 at 10:20:06AM +0200, Julien Panis wrote:
>> This PFSM controls the operational modes of the PMIC:
>> - STANDBY and LP_STANDBY,
>> - ACTIVE state,
>> - MCU_ONLY state,
>> - RETENTION state, with or without DDR and/or GPIO retention.
>> Depending on the current operational mode, some voltage domains
>> remain energized while others can be off.
>>
>> This PFSM is also used to trigger a firmware update, and provides
>> R/W access to device registers.
> What userspace code uses these new ioctls?  Do you have a pointer to it
> anywhere?

I will provide a user app in 'samples' directory in v6.

>
>> --- /dev/null
>> +++ b/include/uapi/linux/tps6594_pfsm.h
>> @@ -0,0 +1,45 @@
>> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
>> +/*
>> + * Userspace ABI for TPS6594 PMIC Pre-configurable Finite State Machine
>> + *
>> + * Copyright (C) 2023 BayLibre Incorporated - https://www.baylibre.com/
>> + */
>> +
>> +#ifndef __TPS6594_PFSM_H
>> +#define __TPS6594_PFSM_H
>> +
>> +#include <linux/const.h>
>> +#include <linux/ioctl.h>
>> +#include <linux/types.h>
>> +
>> +/* PFSM state definitions */
>> +enum pfsm_state {
>> +	PMIC_ACTIVE_STATE,
>> +	PMIC_MCU_ONLY_STATE,
>> +	PMIC_RETENTION_STATE
>> +};
>> +
>> +/**
>> + * struct pmic_state - PMIC state identification
>> + * @state:   PFSM destination state
>> + * @options: options for destination state
>> + */
>> +struct pmic_state {
>> +	enum pfsm_state state;
>> +	__u8 options;
>> +};
>> +
>> +/* Commands */
>> +#define	PMIC_BASE			'P'
>> +
>> +#define	PMIC_GOTO_STANDBY		_IO(PMIC_BASE, 0)
>> +#define	PMIC_GOTO_LP_STANDBY		_IO(PMIC_BASE, 1)
>> +#define	PMIC_UPDATE_PGM			_IO(PMIC_BASE, 2)
>> +#define	PMIC_SET_STATE			_IOW(PMIC_BASE, 3, struct pmic_state)
>> +
>> +/* Options for destination state */
>> +#define PMIC_GPIO_RETENTION		_BITUL(0)
>> +#define PMIC_DDR_RETENTION		_BITUL(1)
>> +#define PMIC_MCU_ONLY_STARTUP_DEST	_BITUL(2)
> Please read Documentation/driver-api/ioctl.rst which says:
>
> * Bitfields and enums generally work as one would expect them to,
>    but some properties of them are implementation-defined, so it is
>    better to avoid them completely in ioctl interfaces.
>
> For a brand-new ioctl interface, you did both of these unrecommended
> things.  Why set yourself for complexity when you do not need to?

I will fix that. Thank you for your feedback.

Julien