Re: [PATCH 5.3 regression fix] pwm: Fallback to the static lookup-list when acpi_pwm_get fails

[Hans de Goede <hdegoede@redhat.com>]

Thierry,

Ping? This fixes a somewhat serious regression in 5.3, can we please get
this queued up for merging into 5.3 ?

Regards,

Hans

On 30-07-19 17:48, 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.Thieer
> 
> 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.
> 
> BugLink: https://bugs.freedesktop.org/show_bug.cgi?id=96571
> Reported-by: youling257@gmail.com
> Fixes: 4a6ef8e37c4d ("pwm: Add support referencing PWMs from ACPI")
> Cc: Nikolaus Voss <nikolaus.voss@loewensteinmedical.de>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
>   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
>