On Tue, Jul 30, 2019 at 05:48:48PM +0200, Hans de Goede wrote:
> Commit 4a6ef8e37c4d ("pwm: Add support referencing PWMs from ACPI")
> made pwm_get unconditionally return the acpi_pwm_get return value if
> the device passed to pwm_get has an ACPI fwnode.
>
> But even if the passed in device has an ACPI fwnode, it does not
> necessarily have the necessary ACPI package defining its pwm bindings,
> especially since the binding / API of this ACPI package has only been
> introduced very recently.
>
> Up until now X86/ACPI devices which use a separate pwm controller for
> controlling their LCD screen's backlight brightness have been relying
> on the static lookup-list to get their pwm.
>
> pwm_get unconditionally returning the acpi_pwm_get return value breaks
> this, breaking backlight control on these devices.
>
> This commit fixes this by making pwm_get fall back to the static
> lookup-list if acpi_pwm_get returns -ENOENT.
>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
Perhaps, we may switch to swnode API instead of lookup tables in the future?
> BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=96571
> Reported-by: youling257@xxxxxxxxx
> Fixes: 4a6ef8e37c4d ("pwm: Add support referencing PWMs from ACPI")
> Cc: Nikolaus Voss <nikolaus.voss@xxxxxxxxxxxxxxxxxxxxx>
> Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
> ---
> drivers/pwm/core.c | 7 +++++--
> 1 file changed, 5 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pwm/core.c b/drivers/pwm/core.c
> index c3ab07ab31a9..8edfac17364e 100644
> --- a/drivers/pwm/core.c
> +++ b/drivers/pwm/core.c
> @@ -882,8 +882,11 @@ struct pwm_device *pwm_get(struct device *dev, const char *con_id)
> return of_pwm_get(dev, dev->of_node, con_id);
>
> /* then lookup via ACPI */
> - if (dev && is_acpi_node(dev->fwnode))
> - return acpi_pwm_get(dev->fwnode);
> + if (dev && is_acpi_node(dev->fwnode)) {
> + pwm = acpi_pwm_get(dev->fwnode);
> + if (!IS_ERR(pwm) || PTR_ERR(pwm) != -ENOENT)
> + return pwm;
> + }
>
> /*
> * We look up the provider in the static table typically provided by
> --
> 2.21.0
>
--
With Best Regards,
Andy Shevchenko
