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SubjectRe: [PATCH] pmbus: added possibility to change timeout for device update
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On 11/02/2017 04:31 AM, Romain Porte wrote:
> By default the time before really updating a device is hardcoded to one second
> in the pmbus_core.c file (HZ). This patch proposes a new configuration entry
> that allows to tune the timeout value before updating a device. It defaults
> to one second in order to stay compatible with the previous behavior, but can
> now be changed if needed.
>
> Performing faster than one second sensor reads in userspace is what motivates
> this patch.
>
> Reviewed-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>

NACK, I'd rather drop the caching entirely, and possibly convert the driver to
regmap for caching non-volatile registers.

Guenter

> ---
> drivers/hwmon/pmbus/Kconfig | 15 +++++++++++++++
> drivers/hwmon/pmbus/pmbus_core.c | 5 ++++-
> 2 files changed, 19 insertions(+), 1 deletion(-)
>
> diff --git a/drivers/hwmon/pmbus/Kconfig b/drivers/hwmon/pmbus/Kconfig
> index 40019325b517..5d865e3d0cb1 100644
> --- a/drivers/hwmon/pmbus/Kconfig
> +++ b/drivers/hwmon/pmbus/Kconfig
> @@ -14,6 +14,21 @@ menuconfig PMBUS
>
> if PMBUS
>
> +config PMBUS_DEV_CACHE_MS
> + int "PMBus device read cache in milliseconds"
> + default 1000
> + help
> + This options allows you to control how much time should a device
> + be stored in cache before being updated. If you attempt to read
> + a sensor value from the device before this cache time is elapsed,
> + then you will get a cached value and the driver will not update
> + the device values.
> +
> + This option is using jiffies under the hood and thus is not very
> + precise. Setting this option to more than zero will perform a delay
> + of at least one jiffie. Setting this option to zero will lead to
> + no delay, thus forcing to perform an update on every read.
> +
> config SENSORS_PMBUS
> tristate "Generic PMBus devices"
> default y
> diff --git a/drivers/hwmon/pmbus/pmbus_core.c b/drivers/hwmon/pmbus/pmbus_core.c
> index 302f0aef59de..2df0bc5a46f1 100644
> --- a/drivers/hwmon/pmbus/pmbus_core.c
> +++ b/drivers/hwmon/pmbus/pmbus_core.c
> @@ -414,9 +414,12 @@ static struct pmbus_data *pmbus_update_device(struct device *dev)
> struct pmbus_data *data = i2c_get_clientdata(client);
> const struct pmbus_driver_info *info = data->info;
> struct pmbus_sensor *sensor;
> + unsigned long timeout;
>
> mutex_lock(&data->update_lock);
> - if (time_after(jiffies, data->last_updated + HZ) || !data->valid) {
> + timeout = data->last_updated +
> + (HZ * CONFIG_PMBUS_DEV_CACHE_MS + 999) / 1000;
> + if (time_after(jiffies, timeout) || !data->valid) {
> int i, j;
>
> for (i = 0; i < info->pages; i++) {
>

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