Hi Sakari,
On Wed, Aug 26, 2020 at 02:54:27PM +0300, Sakari Ailus wrote:
> Enable drivers to tell ACPI that there's no need to power on a device for
> probe. Drivers should still perform this by themselves if there's a need
> to. In some cases powering on the device during probe is undesirable, and
> this change enables a driver to choose what fits best for it.
>
> Add a field called "flags" into struct i2c_driver for driver flags, and a
> flag I2C_DRV_FL_ALLOW_LOW_POWER_PROBE to tell a driver supports probe in
> low power state.
>
> Signed-off-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> ---
> drivers/i2c/i2c-core-base.c | 18 +++++++++++++++---
> include/linux/i2c.h | 14 ++++++++++++++
> 2 files changed, 29 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/i2c/i2c-core-base.c b/drivers/i2c/i2c-core-base.c
> index 34a9609f256da..f2683790eb0d2 100644
> --- a/drivers/i2c/i2c-core-base.c
> +++ b/drivers/i2c/i2c-core-base.c
> @@ -436,6 +436,15 @@ static int i2c_smbus_host_notify_to_irq(const struct i2c_client *client)
> return irq > 0 ? irq : -ENXIO;
> }
>
> +static bool allow_low_power_probe(struct device *dev)
> +{
> + struct i2c_driver *driver = to_i2c_driver(dev->driver);
> +
> + return driver->flags & I2C_DRV_FL_ALLOW_LOW_POWER_PROBE &&
> + is_acpi_node(dev_fwnode(dev)) &&
> + device_property_present(dev, "allow-low-power-probe");
So, I wondered about potential DT usage and I read the discussion about
that in v5 which concluded that for the DT case, the drivers can make
use of the binding individually. I can agree to that, but then the name
of the binding is probably problematic. 'allow-*' sounds like
configuration but DT is for describing HW. So, I think something in the
range of 'keep-low-power' or so might be better suited. Grepping shows
there already is a generic binding "low-power-enable". Not sure, if it
really fits, because here it is more about 'keeping' rather than
enabling. Or?
> +/**
> + * enum i2c_driver_flags - Flags for an I2C device driver
> + *
> + * @I2C_DRV_FL_ALLOW_LOW_POWER_PROBE: Let the ACPI driver manage the device's
> + * power state during probe and remove
> + */
> +enum i2c_driver_flags {
> + I2C_DRV_FL_ALLOW_LOW_POWER_PROBE = BIT(0),
> +};
> +
> /**
> * struct i2c_driver - represent an I2C device driver
> * @class: What kind of i2c device we instantiate (for detect)
> @@ -231,6 +242,7 @@ enum i2c_alert_protocol {
> * @detect: Callback for device detection
> * @address_list: The I2C addresses to probe (for detect)
> * @clients: List of detected clients we created (for i2c-core use only)
> + * @flags: A bitmask of flags defined in &enum i2c_driver_flags
> *
> * The driver.owner field should be set to the module owner of this driver.
> * The driver.name field should be set to the name of this driver.
> @@ -289,6 +301,8 @@ struct i2c_driver {
> int (*detect)(struct i2c_client *client, struct i2c_board_info *info);
> const unsigned short *address_list;
> struct list_head clients;
> +
> + unsigned int flags;
Here I wonder if all this is really I2C specific? I could imagine this
being useful for other busses as well, so maybe 'struct device_driver'
is a better place?
Thanks for this work!
All the best,
Wolfram
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