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SubjectRe: [PATCH v2] video: backlight: pwm_bl: Initialize fb_bl_on[x] and use_count during pwm_backlight_probe()
Adding Jingoo.

On Tue, 01 Nov 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 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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