linux-kernel - Re: [PATCH] video: backlight: Remove backlight sysfs uevent

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Date:	Tue, 12 Nov 2013 09:18:04 +0900
From:	Jingoo Han <jg1.han@...sung.com>
To:	'Kyungmin Park' <kmpark@...radead.org>,
	'Henrique de Moraes Holschuh' <ibm-acpi@....eng.br>
Cc:	linux-fbdev@...r.kernel.org, linux-kernel@...r.kernel.org,
	kay@...y.org, 'Richard Purdie' <rpurdie@...ys.net>,
	'Jingoo Han' <jg1.han@...sung.com>,
	ibm-acpi-devel@...ts.sourceforge.net,
	platform-driver-x86@...r.kernel.org
Subject: Re: [PATCH] video: backlight: Remove backlight sysfs uevent

On Tuesday, November 12, 2013 8:57 AM, Kyungmin Park wrote:
> 
> From: Kyungmin Park <kyungmin.park@...sung.com>
> 
> The most mobile phones have Ambient Light Sensors and it changes brightness according lux.
> It means it changes backlight brightness frequently by just writing sysfs node, so it generates uevent.
> 
> Usually there's no user to use this backlight changes. But it forks udev worker threads and it takes
> about 5ms. The main problem is that it hurts other process activities. so remove it.
> 
> Kay said
> "Uevents are for the major, low-frequent, global device state-changes,
>  not for carrying-out any sort of measurement data. Subsystems which
>  need that should use other facilities like poll()-able sysfs file or
>  any other subscription-based, client-tracking interface which does not
>  cause overhead if it isn't used. Uevents are not the right thing to
>  use here, and upstream udev should not paper-over broken kernel
>  subsystems."
> 
> Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
> ---
> diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c
> index 94a403a..441272d 100644
> --- a/drivers/video/backlight/backlight.c
> +++ b/drivers/video/backlight/backlight.c
> @@ -88,9 +88,6 @@ static void backlight_generate_event(struct backlight_device *bd,
>  	char *envp[2];
> 
>  	switch (reason) {
> -	case BACKLIGHT_UPDATE_SYSFS:
> -		envp[0] = "SOURCE=sysfs";
> -		break;
>  	case BACKLIGHT_UPDATE_HOTKEY:
>  		envp[0] = "SOURCE=hotkey";
>  		break;
> @@ -172,8 +169,6 @@ static ssize_t brightness_store(struct device *dev,
>  	}
>  	mutex_unlock(&bd->ops_lock);
> 
> -	backlight_generate_event(bd, BACKLIGHT_UPDATE_SYSFS);
> -
>  	return rc;
>  }
>  static DEVICE_ATTR_RW(brightness);
> diff --git a/include/linux/backlight.h b/include/linux/backlight.h
> index 53b7794..d2a27dd 100644
> --- a/include/linux/backlight.h
> +++ b/include/linux/backlight.h
> @@ -29,7 +29,6 @@
> 
>  enum backlight_update_reason {
>  	BACKLIGHT_UPDATE_HOTKEY,
> -	BACKLIGHT_UPDATE_SYSFS,

+cc Henrique de Moraes Holschuh (Maintainer of thinkpad_acpi)

Hi Henrique de Moraes Holschuh,

'thinkpad_acpi.c' uses the 'BACKLIGHT_UPDATE_SYSFS'.
Henrique, can we remove it?

drivers/platform/x86/thinkpad_acpi.c
if (!rc && ibm_backlight_device)
                backlight_force_update(ibm_backlight_device,
                                        BACKLIGHT_UPDATE_SYSFS);

Best regards,
Jingoo Han

>  };
> 
>  enum backlight_type {

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