linux-kernel - Re: [PATCH 09/15] staging: fbtft: fb_ssd1351.c: Introduce backlight_is

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Date:   Mon, 9 Jan 2023 08:04:08 +0100
From:   Stephen Kitt <steve@....org>
To:     Sam Ravnborg <sam@...nborg.org>
Cc:     Sam Ravnborg via B4 Submission Endpoint 
        <devnull+sam.ravnborg.org@...nel.org>,
        Alexandre Belloni <alexandre.belloni@...tlin.com>,
        linux-staging@...ts.linux.dev,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-fbdev@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Paul Mackerras <paulus@...ba.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Helge Deller <deller@....de>, Lee Jones <lee@...nel.org>,
        Miguel Ojeda <ojeda@...nel.org>,
        Antonino Daplas <adaplas@...il.com>,
        linux-omap@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        Robin van der Gracht <robin@...tonic.nl>,
        Nicolas Ferre <nicolas.ferre@...rochip.com>,
        Jingoo Han <jingoohan1@...il.com>,
        linuxppc-dev@...ts.ozlabs.org,
        Claudiu Beznea <claudiu.beznea@...rochip.com>
Subject: Re: [PATCH 09/15] staging: fbtft: fb_ssd1351.c: Introduce
 backlight_is_blank()

Hi Sam,

On Sun, 8 Jan 2023 21:29:43 +0100, Sam Ravnborg <sam@...nborg.org> wrote:
> On Sun, Jan 08, 2023 at 08:28:17PM +0100, Stephen Kitt wrote:
> > On Sat, 07 Jan 2023 19:26:23 +0100, Sam Ravnborg via B4 Submission
> > Endpoint <devnull+sam.ravnborg.org@...nel.org> wrote:
> >   
> > > From: Sam Ravnborg <sam@...nborg.org>
> > > 
> > > Avoiding direct access to backlight_properties.props.
> > > 
> > > Access to the deprecated props.fb_blank replaced by
> > > backlight_is_blank(). Access to props.power is dropped - it was only
> > > used for debug.
> > > 
> > > Signed-off-by: Sam Ravnborg <sam@...nborg.org>
> > > Cc: Stephen Kitt <steve@....org>
> > > Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
> > > Cc: Daniel Thompson <daniel.thompson@...aro.org>
> > > Cc: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> > > Cc: linux-fbdev@...r.kernel.org
> > > ---
> > >  drivers/staging/fbtft/fb_ssd1351.c | 9 +++------
> > >  1 file changed, 3 insertions(+), 6 deletions(-)
> > > 
> > > diff --git a/drivers/staging/fbtft/fb_ssd1351.c
> > > b/drivers/staging/fbtft/fb_ssd1351.c index b8d55aa8c5c7..995fbd2f3dc6
> > > 100644 --- a/drivers/staging/fbtft/fb_ssd1351.c
> > > +++ b/drivers/staging/fbtft/fb_ssd1351.c
> > > @@ -190,15 +190,12 @@ static struct fbtft_display display = {
> > >  static int update_onboard_backlight(struct backlight_device *bd)
> > >  {
> > >  	struct fbtft_par *par = bl_get_data(bd);
> > > -	bool on;
> > > +	bool blank = backlight_is_blank(bd);
> > >  
> > > -	fbtft_par_dbg(DEBUG_BACKLIGHT, par,
> > > -		      "%s: power=%d, fb_blank=%d\n",
> > > -		      __func__, bd->props.power, bd->props.fb_blank);
> > > +	fbtft_par_dbg(DEBUG_BACKLIGHT, par, "%s: blank=%d\n", __func__,
> > > blank); 
> > > -	on = !backlight_is_blank(bd);
> > >  	/* Onboard backlight connected to GPIO0 on SSD1351, GPIO1
> > > unused */
> > > -	write_reg(par, 0xB5, on ? 0x03 : 0x02);
> > > +	write_reg(par, 0xB5, !blank ? 0x03 : 0x02);
> > >  
> > >  	return 0;
> > >  }
> > > 
> > > -- 
> > > 2.34.1  
> > 
> > For debugging purposes here, would there be any point in logging
> > props.state? As in
> > 
> >         fbtft_par_dbg(DEBUG_BACKLIGHT, par,
> > -                     "%s: power=%d, fb_blank=%d\n",
> > -                     __func__, bd->props.power, bd->props.fb_blank);
> > +                     "%s: power=%d, state=%u\n",
> > +                     __func__, bd->props.power, bd->props.state);  
> 
> Thanks for the suggestion - and the reviews!
> 
> I was tempted to just remove the debugging.
> If we require debugging, then this could be added in the backlight core,
> thus everyone would benefit from it.
> 
> The solution above avoid any direct use of backlight_properties
> which I consider a layer violation outside the backlight core.
> (We cannot avoid it today with the current interface - but we can
> minimize it).

Ah yes, ideally backlight_properties should be viewed as an opaque structure,
that makes sense.

Regards,

Stephen

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