Date: Tue, 8 Nov 2016 23:25:25 +0100
From: Lukasz Majewski <l.majewski@majess.pl>
To: Thierry Reding <thierry.reding@gmail.com>,
        Lee Jones <lee.jones@linaro.org>,
        Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>,
        Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: linux-pwm@vger.kernel.org, linux-kernel@vger.kernel.org,
        Fabio Estevam <fabio.estevam@nxp.com>,
        Fabio Estevam <festevam@gmail.com>, <linux-fbdev@vger.kernel.org>,
        Liu Ying <Ying.Liu@freescale.com>
Subject: Re: [PATCH v2] video: backlight: pwm_bl: Initialize fb_bl_on[x] and
 use_count during pwm_backlight_probe()
Message-ID: <20161108232525.639ea49f@jawa>
In-Reply-To: <1477985147-18835-1-git-send-email-l.majewski@majess.pl>
References: <1477169904-14997-1-git-send-email-l.majewski@majess.pl>
        <1477985147-18835-1-git-send-email-l.majewski@majess.pl>
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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.
>=20
> Unfortunately, pwm_bl driver's probe did not initialize members of
> struct backlight_device necessary for further blank/unblank operation.
>=20
> This code in case of initial unblank of backlight device (default=20
> 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).
>=20
> 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 :-)

Best regards,
=C5=81ukasz Majewski

>=20
> 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
>=20
> ---
>  drivers/video/backlight/pwm_bl.c | 10 +++++++++-
>  1 file changed, 9 insertions(+), 1 deletion(-)
>=20
> 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 =3D FB_BLANK_UNBLANK;
>  	struct pwm_args pargs;
> -	int ret;
> +	int ret, i;
> =20
>  	if (!data) {
>  		ret =3D pwm_backlight_parse_dt(&pdev->dev, &defdata);
> @@ -348,6 +348,14 @@ static int pwm_backlight_probe(struct
> platform_device *pdev)=20
>  	bl->props.brightness =3D data->dft_brightness;
>  	bl->props.power =3D initial_blank;
> +
> +	if (initial_blank =3D=3D FB_BLANK_UNBLANK) {
> +		for (i =3D 0; i < FB_MAX; i++)
> +			bl->fb_bl_on[i] =3D true;
> +
> +		bl->use_count =3D 1;
> +	}
> +
>  	backlight_update_status(bl);
> =20
>  	platform_set_drvdata(pdev, bl);


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