On Wed, 17 May 2017, Sudip Mukherjee wrote:
> It is possible to update the backlight power and the brightness using
> the sysfs and on writing it either returns the count or if the callback
> function does not exist then returns the error code 'ENXIO'.
>
> We have a situation where the userspace client is writing to the sysfs
> to update the power and since the callback function exists the client
> receives the return value as count and considers the operation to be
> successful. That is correct as the write to the sysfs was successful.
> But there is no way to know if the actual operation was done or not.
>
> backlight_update_status() returns the error code if it fails. Pass that
> to the userspace client who is trying to update the power so that the
> client knows that the operation failed.
>
> Acked-by: Daniel Thompson <daniel.thompson@xxxxxxxxxx>
> Signed-off-by: Sudip Mukherjee <sudip.mukherjee@xxxxxxxxxxxxxxx>
> ---
>
> v5: dropped the ternary condition
> v4: ABI comment removed from commit message
> v3: remove rc = 0, and update rc with count in else condition.
> v2: update power with old value on failure.
>
> drivers/video/backlight/backlight.c | 15 ++++++++++-----
> 1 file changed, 10 insertions(+), 5 deletions(-)
Applied, thanks.
> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 288318a..8049e76 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -134,7 +134,7 @@ static ssize_t bl_power_store(struct device *dev, struct device_attribute *attr,
> {
> int rc;
> struct backlight_device *bd = to_backlight_device(dev);
> - unsigned long power;
> + unsigned long power, old_power;
>
> rc = kstrtoul(buf, 0, &power);
> if (rc)
> @@ -145,10 +145,16 @@ static ssize_t bl_power_store(struct device *dev, struct device_attribute *attr,
> if (bd->ops) {
> pr_debug("set power to %lu\n", power);
> if (bd->props.power != power) {
> + old_power = bd->props.power;
> bd->props.power = power;
> - backlight_update_status(bd);
> + rc = backlight_update_status(bd);
> + if (rc)
> + bd->props.power = old_power;
> + else
> + rc = count;
> + } else {
> + rc = count;
> }
> - rc = count;
> }
> mutex_unlock(&bd->ops_lock);
>
> @@ -176,8 +182,7 @@ int backlight_device_set_brightness(struct backlight_device *bd,
> else {
> pr_debug("set brightness to %lu\n", brightness);
> bd->props.brightness = brightness;
> - backlight_update_status(bd);
> - rc = 0;
> + rc = backlight_update_status(bd);
> }
> }
> mutex_unlock(&bd->ops_lock);
--
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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