[03/12] PM: i2c-designware-platdrv: Use DPM_FLAG_SMART_PREPARE

From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>

Modify i2c-designware-platdrv to set DPM_FLAG_SMART_PREPARE for its
devices and return 0 from the system suspend ->prepare callback
if the device has an ACPI companion object in order to tell the PM
core and middle layers to avoid skipping system suspend/resume
callbacks for the device in that case (which may be problematic,
because the device may be accessed during suspend and resume of
other devices via I2C operation regions then).

Also the pm_runtime_suspended() check in dw_i2c_plat_prepare()
is not necessary any more, because the core does it when setting
power.direct_complete for the device, so drop it.

Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
---
 drivers/i2c/busses/i2c-designware-platdrv.c |   10 +++++++++-
 1 file changed, 9 insertions(+), 1 deletion(-)

On 16 October 2017 at 03:29, Rafael J. Wysocki <rjw@rjwysocki.net> wrote:
> From: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
>
> Modify i2c-designware-platdrv to set DPM_FLAG_SMART_PREPARE for its
> devices and return 0 from the system suspend ->prepare callback
> if the device has an ACPI companion object in order to tell the PM
> core and middle layers to avoid skipping system suspend/resume
> callbacks for the device in that case (which may be problematic,
> because the device may be accessed during suspend and resume of
> other devices via I2C operation regions then).
>
> Also the pm_runtime_suspended() check in dw_i2c_plat_prepare()
> is not necessary any more, because the core does it when setting
> power.direct_complete for the device, so drop it.
>
> Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>
> ---
>  drivers/i2c/busses/i2c-designware-platdrv.c |   10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>
> Index: linux-pm/drivers/i2c/busses/i2c-designware-platdrv.c
> ===================================================================
> --- linux-pm.orig/drivers/i2c/busses/i2c-designware-platdrv.c
> +++ linux-pm/drivers/i2c/busses/i2c-designware-platdrv.c
> @@ -370,6 +370,8 @@ static int dw_i2c_plat_probe(struct plat
>         ACPI_COMPANION_SET(&adap->dev, ACPI_COMPANION(&pdev->dev));
>         adap->dev.of_node = pdev->dev.of_node;
>
> +       dev_pm_set_driver_flags(&pdev->dev, DPM_FLAG_SMART_PREPARE);
> +
>         /* The code below assumes runtime PM to be disabled. */
>         WARN_ON(pm_runtime_enabled(&pdev->dev));
>
> @@ -433,7 +435,13 @@ MODULE_DEVICE_TABLE(of, dw_i2c_of_match)
>  #ifdef CONFIG_PM_SLEEP
>  static int dw_i2c_plat_prepare(struct device *dev)
>  {
> -       return pm_runtime_suspended(dev);
> +       /*
> +        * If the ACPI companion device object is present for this device, it
> +        * may be accessed during suspend and resume of other devices via I2C
> +        * operation regions, so tell the PM core and middle layers to avoid
> +        * skipping system suspend/resume callbacks for it in that case.
> +        */

The above scenario can also happens for non-acpi companion devices.
That makes this comment a bit confusing to me.

> +       return !has_acpi_companion(dev);

I understand it still works by always returning 1 for the non-acpi
case, because the PM core deals with it for the direct_complete path.
However it looks rather odd, especially due to the comment above.

Perhaps returning pm_runtime_suspended() in the other case make this
more clear? Or perhaps clarifying the comment somehow? :-)

>  }
>
>  static void dw_i2c_plat_complete(struct device *dev)
>
>

Kind regards
Uffe