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

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Date:   Tue, 25 Oct 2016 18:47:00 -0400
From:   "Jingoo Han" <jingoohan1@...il.com>
To:     "'Lukasz Majewski'" <l.majewski@...ess.pl>
Cc:     "'Thierry Reding'" <thierry.reding@...il.com>,
        "'Lee Jones'" <lee.jones@...aro.org>,
        "'Jean-Christophe Plagniol-Villard'" <plagnioj@...osoft.com>,
        "'Tomi Valkeinen'" <tomi.valkeinen@...com>,
        <linux-pwm@...r.kernel.org>, <linux-fbdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>,
        "'Fabio Estevam'" <fabio.estevam@....com>,
        "'Fabio Estevam'" <festevam@...il.com>,
        "'Liu Ying'" <Ying.Liu@...escale.com>
Subject: Re: [PATCH] video: backlight: pwm_bl: Initialize fb_bl_on[x] and use_count during pwm_backlight_probe()

On Monday, October 24, 2016, Lukasz Majewski wrote:
> 
> Hi Jingoo,
> 
> > On Saturday, October 22, 2016, Lukasz Majewski wrote:
> > >
> > > The commit: a55944ca82d287ca099ca90413af857af9086773 has posed some
> > > extra

Please add the 'subject' of patch as below.

The commit a55944ca82d2 ("backlight: update bd state & fb_blank properties when necessary ")
has posted some extra.

Best regards,
Jingoo Han


> >
> > Please add the subject of the patch, in order to let people know
> > which patch you mention exactly. Please loot at other commits that
> > fixed bugs or behavior
> > of other patches.
> 
> Thanks for the tip.
> 
> The mentioned patch:
> 
> commit a55944ca82d287ca099ca90413af857af9086773
> Author: Liu Ying <Ying.Liu@...escale.com>
> Date:   Thu Apr 3 14:48:54 2014 -0700
> 
>     backlight: update bd state & fb_blank properties when necessary
> 
>     We don't have to update the state and fb_blank properties of a
> backlight
>     device every time a blanking or unblanking event comes because they
> may
>     have already been what we want.  Another thought is that one backlight
>     device may be shared by multiple framebuffers.  The backlight driver
>     should take the backlight device as a resource shared by all the
>     associated framebuffers.
> 
>     This patch adds some logic to record each framebuffer's backlight
> usage
>     to determine the backlight device use count and whether the two
>     properties should be updated or not.  To be more specific, only one
>     unblank operation on a certain blanked framebuffer may increase the
>     backlight device's use count by one, while one blank operation on a
>     certain unblanked framebuffer may decrease the use count by one,
> because
>     the userspace is likely to unblank an unblanked framebuffer or blank a
>     blanked framebuffer.
> 
> 
> Could you provide more feedback regarding provided fix?
> 
> Thanks in advance,
> 
> Łukasz Majewski
> 
> >
> > > 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.
> > >
> > >
> > > Signed-off-by: Lukasz Majewski <l.majewski@...ess.pl>
> > > ---
> > > The patch has been tested on i.MX6q with vanilla 4.7 and 4.8
> > > kernels. It applies on 4.9-rcX SHA1:
> > > dcd4693cf47801b7d988ea897519de90dfd25d17.
> > >
> > > ---
> > >  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 8040fd6..def39e8 100644
> > > --- a/drivers/video/backlight/pwm_bl.c
> > > +++ b/drivers/video/backlight/pwm_bl.c
> > > @@ -203,7 +203,7 @@ 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); @@ - 349,6 +349,14 @@ 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);
> > > --
> > > 2.1.4
> >
> >