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From: Nikolaus Voss <nv@vosn.de>
To: Hans de Goede <hdegoede@redhat.com>
Cc: Thierry Reding <thierry.reding@gmail.com>,
	Andy Shevchenko <andriy.shevchenko@linux.intel.com>,
	"linux-pwm@vger.kernel.org" <linux-pwm@vger.kernel.org>,
	"linux-acpi@vger.kernel.org" <linux-acpi@vger.kernel.org>,
	"youling257@gmail.com" <youling257@gmail.com>,
	nikolaus.voss@loewensteinmedical.de
Subject: Re: [PATCH 5.3 regression fix] pwm: Fallback to the static lookup-list when acpi_pwm_get fails
Date: Mon, 5 Aug 2019 11:31:27 +0200 (CEST)	[thread overview]
Message-ID: <alpine.DEB.2.20.1908050935570.62587@fox.voss.local> (raw)
In-Reply-To: <20190730154848.5164-1-hdegoede@redhat.com>

Hi Hans,

On Tue, 30 Jul 2019, 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.

Ok, I didn't find any pwm_add_table() calls in the x86 directory, so I 
thought the fallback matching is only for non-DT/non-ACPI systems. If it 
is used for ACPI nodes without PWM controller binding, it maybe should 
apply to DT nodes without PWM controller binding, too?

It would be structurally cleaner as DT and ACPI handling was symmetrical.

Niko

>
> 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
> --
> 2.21.0
>
>

  parent reply	other threads:[~2019-08-05  9:31 UTC|newest]

Thread overview: 8+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-07-30 15:48 [PATCH 5.3 regression fix] pwm: Fallback to the static lookup-list when acpi_pwm_get fails Hans de Goede
2019-07-30 16:08 ` Andy Shevchenko
2019-08-05  9:31 ` Nikolaus Voss [this message]
2019-08-05  9:55   ` Hans de Goede
2019-08-05 10:11     ` Nikolaus Voss
2019-08-08 10:19 ` Hans de Goede
2019-08-08 11:21   ` Thierry Reding
2019-08-08 12:14     ` Hans de Goede

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