On Sat, May 6, 2017 at 12:33 AM, Sudip Mukherjee
<sudipm.mukherjee@xxxxxxxxx> 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.
>
> This is not a change of ABI as the userspace expects an error of ENXIO,
> after this patch the range of errors that are returned to the userspace
> will increase.
One nit.
> @@ -143,12 +143,16 @@ static ssize_t bl_power_store(struct device *dev, struct device_attribute *attr,
> rc = -ENXIO;
> mutex_lock(&bd->ops_lock);
> if (bd->ops) {
> + rc = 0;
You may remove this...
> 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;
> }
> - rc = count;
> + rc = rc ? rc : count;
... and replace this by
} else
rc = count;
--
With Best Regards,
Andy Shevchenko
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