linux-kernel - Re: [PATCH v2] video: backlight: pwm_bl: Initialize fb_bl_on[x] and use_count during pwm_backlight

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Date:   Thu, 10 Nov 2016 08:16:15 +0000
From:   Lee Jones <lee.jones@...aro.org>
To:     Lukasz Majewski <l.majewski@...ess.pl>
Cc:     Thierry Reding <thierry.reding@...il.com>,
        Jean-Christophe Plagniol-Villard <plagnioj@...osoft.com>,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        linux-pwm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Fabio Estevam <fabio.estevam@....com>,
        Fabio Estevam <festevam@...il.com>,
        linux-fbdev@...r.kernel.org, Liu Ying <Ying.Liu@...escale.com>
Subject: Re: [PATCH v2] video: backlight: pwm_bl: Initialize fb_bl_on[x] and
 use_count during pwm_backlight_probe()

On Tue, 08 Nov 2016, Lukasz Majewski wrote:

> Dear All,
> 
> > The commit a55944ca82d2 ("backlight: update bd state & fb_blank
> > properties when necessary") has posed some extra restrictions on
> > blanking and unblanking frame buffer device.
> > 
> > Unfortunately, pwm_bl driver's probe did not initialize members of
> > struct backlight_device necessary for further blank/unblank operation.
> > 
> > This code in case of initial unblank of backlight device (default 
> > behaviour) sets use_count to 1 and marks this particular backlight
> > device as used by all available fb devices (since it is not known
> > during probe how much and which fb devices will be assigned).
> > 
> > Without this code, the backlight works properly until one tries to
> > blank it manually from sysfs with "echo 1
> > > /sys/class/graphics/fb0/blank". Since fb_bl_on[0] and use_count
> > > were both set to 0, the logic at
> > fb_notifier_callback (@backlight.c) thought that we didn't turn on
> > (unblanked) the backlight device and refuses to disable (blank) it.
> > As a result we see garbage from fb displayed.
> 
> COmments/acks are more than welcome :-)

Ah, it looks like you dropped Jingoo from the list!

I'll reply to the original mail with him in CC.

> > Signed-off-by: Lukasz Majewski <l.majewski@...ess.pl>
> > ---
> > The patch has been tested on i.MX6q with 4.9-rc3
> > SHA1: a909d3e636995ba7c349e2ca5dbb528154d4ac30
> > ---
> > Changes for v2:
> > - Update commit message with proper other commit reference
> > 
> > ---
> >  drivers/video/backlight/pwm_bl.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> > 
> > diff --git a/drivers/video/backlight/pwm_bl.c
> > b/drivers/video/backlight/pwm_bl.c index 1261400..6859ba0 100644
> > --- a/drivers/video/backlight/pwm_bl.c
> > +++ b/drivers/video/backlight/pwm_bl.c
> > @@ -202,7 +202,7 @@ static int pwm_backlight_probe(struct
> > platform_device *pdev) struct pwm_bl_data *pb;
> >  	int initial_blank = FB_BLANK_UNBLANK;
> >  	struct pwm_args pargs;
> > -	int ret;
> > +	int ret, i;
> >  
> >  	if (!data) {
> >  		ret = pwm_backlight_parse_dt(&pdev->dev, &defdata);
> > @@ -348,6 +348,14 @@ static int pwm_backlight_probe(struct
> > platform_device *pdev) 
> >  	bl->props.brightness = data->dft_brightness;
> >  	bl->props.power = initial_blank;
> > +
> > +	if (initial_blank == FB_BLANK_UNBLANK) {
> > +		for (i = 0; i < FB_MAX; i++)
> > +			bl->fb_bl_on[i] = true;
> > +
> > +		bl->use_count = 1;
> > +	}
> > +
> >  	backlight_update_status(bl);
> >  
> >  	platform_set_drvdata(pdev, bl);
> 



-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org │ Open source software for ARM SoCs
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