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SubjectRe: [PATCH v2 RESEND] video: backlight: pwm_bl: Initialize fb_bl_on[x] and use_count during pwm_backlight_probe()
Dear All,

> Thierry, Jingoo,
>
> Please respond to Lukasz.

Yes, your response is more than welcome....... :-)

Thanks in advance,

Łukasz Majewski

>
> On Mon, 26 Dec 2016, Lukasz Majewski wrote:
>
> > 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.
> >
> > Signed-off-by: Lukasz Majewski <l.majewski@majess.pl>
> > ---
> > The patch has been tested on i.MX6q with vanilla 4.9 kernel.
> > It applies on 4.10-rc1.
> > ---
> > 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);
>

Best regards,

Lukasz Majewski

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