On Nov 30 2016 or thereabouts, Brian Norris wrote:
> We need to power on the digitizer before using it, and it's also nice to
> save power in suspend by disabling it. Support an optional "vdd-supply"
> and wire it up for the new Wacom device.
> 
> Wacom recommended waiting up to 100ms after powering on before trying to
> access this device.
> 
> Signed-off-by: Brian Norris <briannor...@chromium.org>
> Signed-off-by: Caesar Wang <w...@rock-chips.com>
> Cc: Jiri Kosina <ji...@kernel.org>
> Cc: linux-in...@vger.kernel.org
> ---
> v1 was a few months back. I finally got around to rewriting it based on
> DT binding feedback.
> 
> v2:
>  * support compatible property for wacom, with specific "vdd-supply" name
>  * support the 100ms delay needed for this digitizer
>  * target regulator support only at specific device
> 
>  Documentation/devicetree/bindings/input/hid-over-i2c.txt | 6 +++++-
>  drivers/hid/i2c-hid/i2c-hid.c | 70 
> ++++++++++++++++++++++++++++++++++++++++++-
>  include/linux/i2c/i2c-hid.h   |  6 ++++
>  2 files changed, 75 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/hid/i2c-hid/i2c-hid.c b/drivers/hid/i2c-hid/i2c-hid.c
> index b3ec4f2de875..1bc174f3a788 100644
> --- a/drivers/hid/i2c-hid/i2c-hid.c
> +++ b/drivers/hid/i2c-hid/i2c-hid.c
> @@ -37,7 +37,9 @@
>  #include <linux/mutex.h>
>  #include <linux/acpi.h>
>  #include <linux/of.h>
> +#include <linux/of_device.h>
>  #include <linux/gpio/consumer.h>
> +#include <linux/regulator/consumer.h>
>  
>  #include <linux/i2c/i2c-hid.h>
>  
> @@ -918,10 +920,25 @@ static inline int i2c_hid_acpi_pdata(struct i2c_client 
> *client,
>  #endif
>  
>  #ifdef CONFIG_OF
> +
> +/* of_device_id match data */
> +struct i2c_hid_of_data {
> +     /* Name of supply regulator. */
> +     const char *supply_name;
> +     /* Delay required after powering on device before it is usable. */
> +     int init_delay_ms;
> +};
> +
> +static const struct i2c_hid_of_data wacom_w9013_data = {

Why is the struct "wacom" specific?
If the vdd line is required, I don't see why there is a need to specify
that this is a Wacom specifics. Then Elan, SYnaptics will want the same
and we won't be able to to follow.

> +     .supply_name            = "vdd",
> +     .init_delay_ms          = 100,

If the purpose of this declaration is to set the delay, why isn't this
something provided by the device tree?

> +};
> +
>  static int i2c_hid_of_probe(struct i2c_client *client,
>               struct i2c_hid_platform_data *pdata)
>  {
>       struct device *dev = &client->dev;
> +     const struct i2c_hid_of_data *data = of_device_get_match_data(dev);
>       u32 val;
>       int ret;
>  
> @@ -937,10 +954,33 @@ static int i2c_hid_of_probe(struct i2c_client *client,
>       }
>       pdata->hid_descriptor_address = val;
>  
> +     if (data) {
> +             pdata->init_delay_ms = data->init_delay_ms;
> +             if (data->supply_name) {
> +                     pdata->supply = 
> devm_regulator_get_optional(&client->dev,
> +                                                                 
> data->supply_name);
> +                     if (IS_ERR(pdata->supply)) {
> +                             ret = PTR_ERR(pdata->supply);
> +                             pdata->supply = NULL;
> +                             if (ret == -EPROBE_DEFER)
> +                                     return ret;
> +                             if (ret == -ENODEV)
> +                                     return 0;
> +                             dev_err(dev, "Failed to get %s regulator: %d\n",
> +                                     data->supply_name, ret);
> +                             return ret;
> +                     }
> +             }
> +     }
> +
>       return 0;
>  }
>  
>  static const struct of_device_id i2c_hid_of_match[] = {
> +     {
> +             .compatible = "wacom,w9013",
> +             .data = &wacom_w9013_data,
> +     },

NACK, see 1/2

I don't really like the v2. IMO, v1 was less intrusive (though it was
missing the init_delay_ms).
I believe it's possible to have a generic device tree description which
doesn't require us to adapt the driver for each and every device.

Cheers,
Benjamin

>       { .compatible = "hid-over-i2c" },
>       {},
>  };
> @@ -983,6 +1023,17 @@ static int i2c_hid_probe(struct i2c_client *client,
>               ihid->pdata = *platform_data;
>       }
>  
> +     if (ihid->pdata.supply) {
> +             ret = regulator_enable(ihid->pdata.supply);
> +             if (ret < 0) {
> +                     dev_err(&client->dev, "Failed to enable regulator: 
> %d\n",
> +                             ret);
> +                     return ret;
> +             }
> +             if (ihid->pdata.init_delay_ms)
> +                     msleep(ihid->pdata.init_delay_ms);
> +     }
> +
>       if (client->irq > 0) {
>               ihid->irq = client->irq;
>       } else if (ACPI_COMPANION(&client->dev)) {
> @@ -1100,6 +1151,9 @@ static int i2c_hid_remove(struct i2c_client *client)
>       if (ihid->desc)
>               gpiod_put(ihid->desc);
>  
> +     if (ihid->pdata.supply)
> +             regulator_disable(ihid->pdata.supply);
> +
>       kfree(ihid);
>  
>       acpi_dev_remove_driver_gpios(ACPI_COMPANION(&client->dev));
> @@ -1152,6 +1206,11 @@ static int i2c_hid_suspend(struct device *dev)
>               else
>                       hid_warn(hid, "Failed to enable irq wake: %d\n",
>                               wake_status);
> +     } else if (ihid->pdata.supply) {
> +             ret = regulator_disable(ihid->pdata.supply);
> +             if (ret < 0)
> +                     hid_warn(hid, "Failed to disable supply: %d\n",
> +                              ret);
>       }
>  
>       return 0;
> @@ -1165,7 +1224,16 @@ static int i2c_hid_resume(struct device *dev)
>       struct hid_device *hid = ihid->hid;
>       int wake_status;
>  
> -     if (device_may_wakeup(&client->dev) && ihid->irq_wake_enabled) {
> +     if (!device_may_wakeup(&client->dev)) {
> +             if (ihid->pdata.supply) {
> +                     ret = regulator_enable(ihid->pdata.supply);
> +                     if (ret < 0)
> +                             hid_warn(hid, "Failed to enable supply: %d\n",
> +                                      ret);
> +                     if (ihid->pdata.init_delay_ms)
> +                             msleep(ihid->pdata.init_delay_ms);
> +             }
> +     } else if (ihid->irq_wake_enabled) {
>               wake_status = disable_irq_wake(ihid->irq);
>               if (!wake_status)
>                       ihid->irq_wake_enabled = false;
> diff --git a/include/linux/i2c/i2c-hid.h b/include/linux/i2c/i2c-hid.h
> index 7aa901d92058..97688cde4a91 100644
> --- a/include/linux/i2c/i2c-hid.h
> +++ b/include/linux/i2c/i2c-hid.h
> @@ -14,9 +14,13 @@
>  
>  #include <linux/types.h>
>  
> +struct regulator;
> +
>  /**
>   * struct i2chid_platform_data - used by hid over i2c implementation.
>   * @hid_descriptor_address: i2c register where the HID descriptor is stored.
> + * @supply: regulator for powering on the device.
> + * @init_delay_ms: delay after powering on before device is usable.
>   *
>   * Note that it is the responsibility of the platform driver (or the acpi 5.0
>   * driver, or the flattened device tree) to setup the irq related to the 
> gpio in
> @@ -31,6 +35,8 @@
>   */
>  struct i2c_hid_platform_data {
>       u16 hid_descriptor_address;
> +     struct regulator *supply;
> +     int init_delay_ms;
>  };
>  
>  #endif /* __LINUX_I2C_HID_H */
> -- 
> 2.8.0.rc3.226.g39d4020
> 

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