linux-kernel - Re: [PATCH 3/6] backlight/pandora: Stop using BL_CORE

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Date:   Wed, 17 Jan 2018 22:38:19 +0100
From:   Daniel Vetter <daniel@...ll.ch>
To:     Daniel Thompson <daniel.thompson@...aro.org>
Cc:     Daniel Vetter <daniel.vetter@...ll.ch>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Lee Jones <lee.jones@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>,
        Daniel Vetter <daniel.vetter@...el.com>
Subject: Re: [PATCH 3/6] backlight/pandora: Stop using BL_CORE_DRIVER1

Thanks a lot for your comments.

On Wed, Jan 17, 2018 at 04:47:41PM +0000, Daniel Thompson wrote:
> On 17/01/18 14:01, Daniel Vetter wrote:
> > Leaking driver internal tracking into the already massively confusing
> > backlight power tracking is really confusing.
> > 
> > Stop that by allocating a tiny driver private data structure instead.
> > 
> > Cc: Lee Jones <lee.jones@...aro.org>
> > Cc: Daniel Thompson <daniel.thompson@...aro.org>
> > Cc: Jingoo Han <jingoohan1@...il.com>
> > Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
> > ---
> >   drivers/video/backlight/pandora_bl.c | 26 +++++++++++++++++++-------
> >   1 file changed, 19 insertions(+), 7 deletions(-)
> > 
> > diff --git a/drivers/video/backlight/pandora_bl.c b/drivers/video/backlight/pandora_bl.c
> > index a186bc677c7d..6bd159946a47 100644
> > --- a/drivers/video/backlight/pandora_bl.c
> > +++ b/drivers/video/backlight/pandora_bl.c
> > @@ -35,11 +35,15 @@
> >   #define MAX_VALUE 63
> >   #define MAX_USER_VALUE (MAX_VALUE - MIN_VALUE)
> > -#define PANDORABL_WAS_OFF BL_CORE_DRIVER1
> > +struct pandora_private {
> > +	unsigned old_state;
> > +#define PANDORABL_WAS_OFF 1
> 
> Nit, but we using old_state like a bitfield so, BIT(0)?
> 
> 
> > +};
> >   static int pandora_backlight_update_status(struct backlight_device *bl)
> >   {
> >   	int brightness = bl->props.brightness;
> > +	struct pandora_private *priv = bl_get_data(bl);
> >   	u8 r;
> >   	if (bl->props.power != FB_BLANK_UNBLANK)
> > @@ -53,7 +57,7 @@ static int pandora_backlight_update_status(struct backlight_device *bl)
> >   		brightness = MAX_USER_VALUE;
> >   	if (brightness == 0) {
> > -		if (bl->props.state & PANDORABL_WAS_OFF)
> > +		if (priv->old_state & PANDORABL_WAS_OFF)
> >   			goto done;
> >   		/* first disable PWM0 output, then clock */
> > @@ -66,7 +70,7 @@ static int pandora_backlight_update_status(struct backlight_device *bl)
> >   		goto done;
> >   	}
> > -	if (bl->props.state & PANDORABL_WAS_OFF) {
> > +	if (priv->old_state & PANDORABL_WAS_OFF) {
> >   		/*
> >   		 * set PWM duty cycle to max. TPS61161 seems to use this
> >   		 * to calibrate it's PWM sensitivity when it starts.
> > @@ -93,9 +97,9 @@ static int pandora_backlight_update_status(struct backlight_device *bl)
> >   done:
> >   	if (brightness != 0)
> > -		bl->props.state &= ~PANDORABL_WAS_OFF;
> > +		priv->old_state 0;
> >   	else
> > -		bl->props.state |= PANDORABL_WAS_OFF;
> > +		priv->old_state = PANDORABL_WAS_OFF;
> 
> Well, we were using it like a bitfield until this bit...

I had a simple boolean first (because that's all we neeed), but that made
the code less readable. Should I s/1/true/ in the #define? The entire C99
bool tends to be a bit a bikeshed sometimes :-)

> 
> 
> >   	return 0;
> >   }
> > @@ -109,15 +113,23 @@ static int pandora_backlight_probe(struct platform_device *pdev)
> >   {
> >   	struct backlight_properties props;
> >   	struct backlight_device *bl;
> > +	struct pandora_private *priv;
> >   	u8 r;
> > +	priv = devm_kmalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> > +	if (!priv) {
> > +		dev_err(&pdev->dev, "failed to allocate driver private data\n");
> > +		return -ENOMEM;
> > +	}
> > +
> >   	memset(&props, 0, sizeof(props));
> >   	props.max_brightness = MAX_USER_VALUE;
> >   	props.type = BACKLIGHT_RAW;
> >   	bl = devm_backlight_device_register(&pdev->dev, pdev->name, &pdev->dev,
> > -					NULL, &pandora_backlight_ops, &props);
> > +					priv, &pandora_backlight_ops, &props);
> >   	if (IS_ERR(bl)) {
> >   		dev_err(&pdev->dev, "failed to register backlight\n");
> > +		kfree(priv);
> 
> Why can't we rely on devres for cleanup?

Argh, I had kmalloc first and then changed to devm_kmalloc. The kfree here
needs to go indeed.

Cheers, Daniel

> 
> 
> >   		return PTR_ERR(bl);
> >   	}
> > @@ -126,7 +138,7 @@ static int pandora_backlight_probe(struct platform_device *pdev)
> >   	/* 64 cycle period, ON position 0 */
> >   	twl_i2c_write_u8(TWL_MODULE_PWM, 0x80, TWL_PWM0_ON);
> > -	bl->props.state |= PANDORABL_WAS_OFF;
> > +	priv->old_state = PANDORABL_WAS_OFF;
> >   	bl->props.brightness = MAX_USER_VALUE;
> >   	backlight_update_status(bl);
> > 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch