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Date: Mon, 29 Aug 2022 11:33:45 -0700
From: Justin Ledford <justinledford@...gle.com>
To: Guenter Roeck <linux@...ck-us.net>
Cc: Jean Delvare <jdelvare@...e.com>, Jonathan Corbet <corbet@....net>,
linux-hwmon@...r.kernel.org, linux-doc@...r.kernel.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] hwmon: (max31790) add fanN_enable
On Mon, Aug 29, 2022 at 11:08 AM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On 8/29/22 10:15, Justin Ledford wrote:
> > On Mon, Aug 29, 2022 at 9:11 AM Guenter Roeck <linux@...ck-us.net> wrote:
> >>
> >> On Mon, Aug 29, 2022 at 08:09:21AM -0700, Justin Ledford wrote:
> >>> The tach input isn't enabled in the device by default. So the only way
> >>> to start using the fan input sensors is to set the regulator mode
> >>> through the driver to RPM mode and then back to whatever mode you
> >>> actually want to use. The I2C interface to the device doesn't couple
> >>> the tach input to the regulator mode so I don't think it makes sense
> >>> for the driver to do this either.
> >>>
> >> Please don't top-post.
> >>
> >> The above does not answer my question why fan_config[] wound need to
> >> be updated repeatedly.
> >>
> >> Guenter
> >>
> >>> On Mon, Aug 29, 2022 at 6:20 AM Guenter Roeck <linux@...ck-us.net> wrote:
> >>>>
> >>>> On Mon, Aug 29, 2022 at 02:43:51AM +0000, Justin Ledford wrote:
> >>>>> The MAX31790 has a tach input enable bit in each fan's configuration
> >>>>> register. This is only enabled by the driver if RPM mode is selected,
> >>>>> but the driver doesn't provide a way to independently enable tachometer
> >>>>> input regardless of the regulator mode.
> >>>>>
> >>>>> By adding the fanN_enable sysfs files, we can decouple the tach input
> >>>>> from the regulator mode. Also update the documentation.
> >>>>>
> >>>>> Signed-off-by: Justin Ledford <justinledford@...gle.com>
> >>>>> ---
> >>>>> Documentation/hwmon/max31790.rst | 1 +
> >>>>> drivers/hwmon/max31790.c | 44 +++++++++++++++++++++++++++-----
> >>>>> 2 files changed, 38 insertions(+), 7 deletions(-)
> >>>>>
> >>>>> diff --git a/Documentation/hwmon/max31790.rst b/Documentation/hwmon/max31790.rst
> >>>>> index 7b097c3b9b90..33c5c7330efc 100644
> >>>>> --- a/Documentation/hwmon/max31790.rst
> >>>>> +++ b/Documentation/hwmon/max31790.rst
> >>>>> @@ -38,6 +38,7 @@ Sysfs entries
> >>>>> fan[1-12]_input RO fan tachometer speed in RPM
> >>>>> fan[1-12]_fault RO fan experienced fault
> >>>>> fan[1-6]_target RW desired fan speed in RPM
> >>>>> +fan[1-6]_enable RW enable or disable the tachometer input
> >>>>> pwm[1-6]_enable RW regulator mode, 0=disabled (duty cycle=0%), 1=manual mode, 2=rpm mode
> >>>>> pwm[1-6] RW read: current pwm duty cycle,
> >>>>> write: target pwm duty cycle (0-255)
> >>>>> diff --git a/drivers/hwmon/max31790.c b/drivers/hwmon/max31790.c
> >>>>> index 7e9362f6dc29..3ae02be4b41e 100644
> >>>>> --- a/drivers/hwmon/max31790.c
> >>>>> +++ b/drivers/hwmon/max31790.c
> >>>>> @@ -118,6 +118,12 @@ static struct max31790_data *max31790_update_device(struct device *dev)
> >>>>> goto abort;
> >>>>> data->target_count[i] = rv;
> >>>>> }
> >>>>> +
> >>>>> + rv = i2c_smbus_read_byte_data(client,
> >>>>> + MAX31790_REG_FAN_CONFIG(i));
> >>>>> + if (rv < 0)
> >>>>> + goto abort;
> >>>>> + data->fan_config[i] = rv;
> >>>>
> >>>> Why is this needed ?
> >>>>
> >>>> Guenter
> >>>>
> >
> > This is needed in case the fan_config is changed outside the driver
> > with something like i2ctransfer, so that the driver reports the actual
> > state of the device, rather than the state at the time of the last
> > write originating from the driver.
> >
>
> That is not a concern or valid argument. With such an argument,
> not a single I2C (or, for that matter, any other) register would
> be cacheable, and much of the caching code in the kernel would
> not work. Anyone hacking around any driver in the system would
> be on their own. One could even argue that such hacking should
> be undone if possible because it may have severe and unexpected
> impact on any driver operation.
>
> Guenter
>
Thank you for the feedback, that makes sense. I will send an updated
patch with this chunk removed.
> >>>>> }
> >>>>>
> >>>>> data->last_updated = jiffies;
> >>>>> @@ -202,6 +208,9 @@ static int max31790_read_fan(struct device *dev, u32 attr, int channel,
> >>>>> }
> >>>>> mutex_unlock(&data->update_lock);
> >>>>> return 0;
> >>>>> + case hwmon_fan_enable:
> >>>>> + *val = !!(data->fan_config[channel] & MAX31790_FAN_CFG_TACH_INPUT_EN);
> >>>>> + return 0;
> >>>>> default:
> >>>>> return -EOPNOTSUPP;
> >>>>> }
> >>>>> @@ -214,7 +223,7 @@ static int max31790_write_fan(struct device *dev, u32 attr, int channel,
> >>>>> struct i2c_client *client = data->client;
> >>>>> int target_count;
> >>>>> int err = 0;
> >>>>> - u8 bits;
> >>>>> + u8 bits, fan_config;
> >>>>> int sr;
> >>>>>
> >>>>> mutex_lock(&data->update_lock);
> >>>>> @@ -243,6 +252,23 @@ static int max31790_write_fan(struct device *dev, u32 attr, int channel,
> >>>>> MAX31790_REG_TARGET_COUNT(channel),
> >>>>> data->target_count[channel]);
> >>>>> break;
> >>>>> + case hwmon_fan_enable:
> >>>>> + fan_config = data->fan_config[channel];
> >>>>> + if (val == 0) {
> >>>>> + fan_config &= ~MAX31790_FAN_CFG_TACH_INPUT_EN;
> >>>>> + } else if (val == 1) {
> >>>>> + fan_config |= MAX31790_FAN_CFG_TACH_INPUT_EN;
> >>>>> + } else {
> >>>>> + err = -EINVAL;
> >>>>> + break;
> >>>>> + }
> >>>>> + if (fan_config != data->fan_config[channel]) {
> >>>>> + err = i2c_smbus_write_byte_data(client, MAX31790_REG_FAN_CONFIG(channel),
> >>>>> + fan_config);
> >>>>> + if (!err)
> >>>>> + data->fan_config[channel] = fan_config;
> >>>>> + }
> >>>>> + break;
> >>>>> default:
> >>>>> err = -EOPNOTSUPP;
> >>>>> break;
> >>>>> @@ -270,6 +296,10 @@ static umode_t max31790_fan_is_visible(const void *_data, u32 attr, int channel)
> >>>>> !(fan_config & MAX31790_FAN_CFG_TACH_INPUT))
> >>>>> return 0644;
> >>>>> return 0;
> >>>>> + case hwmon_fan_enable:
> >>>>> + if (channel < NR_CHANNEL)
> >>>>> + return 0644;
> >>>>> + return 0;
> >>>>> default:
> >>>>> return 0;
> >>>>> }
> >>>>> @@ -423,12 +453,12 @@ static umode_t max31790_is_visible(const void *data,
> >>>>>
> >>>>> static const struct hwmon_channel_info *max31790_info[] = {
> >>>>> HWMON_CHANNEL_INFO(fan,
> >>>>> - HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
> >>>>> - HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
> >>>>> - HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
> >>>>> - HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
> >>>>> - HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
> >>>>> - HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT,
> >>>>> + HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
> >>>>> + HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
> >>>>> + HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
> >>>>> + HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
> >>>>> + HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
> >>>>> + HWMON_F_INPUT | HWMON_F_TARGET | HWMON_F_FAULT | HWMON_F_ENABLE,
> >>>>> HWMON_F_INPUT | HWMON_F_FAULT,
> >>>>> HWMON_F_INPUT | HWMON_F_FAULT,
> >>>>> HWMON_F_INPUT | HWMON_F_FAULT,
> >>>>> --
> >>>>> 2.37.2.672.g94769d06f0-goog
> >>>>>
>
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