linux-kernel - Re: [RFC 2/4] sh: ecovec24: conditionally register backlight device

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Date:   Fri, 16 Mar 2018 16:38:00 -0700
From:   Dmitry Torokhov <dmitry.torokhov@...il.com>
To:     jacopo mondi <jacopo@...ndi.org>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Lee Jones <lee.jones@...aro.org>,
        Daniel Thompson <daniel.thompson@...aro.org>,
        Jingoo Han <jingoohan1@...il.com>, linux-fbdev@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-sh@...r.kernel.org,
        Yoshinori Sato <ysato@...rs.sourceforge.jp>,
        Rich Felker <dalias@...c.org>,
        Linus Walleij <linus.walleij@...aro.org>
Subject: Re: [RFC 2/4] sh: ecovec24: conditionally register backlight device

Hi Jacopo,

On Fri, Mar 16, 2018 at 11:07:48AM +0100, jacopo mondi wrote:
> Hello Dmitry
> 
> FYI I am brushing the ecovec board these days as well
> https://www.spinics.net/lists/linux-sh/msg52536.html
> 

What is the ecovec board BTW? Is it some devkit or what? It seems quite
old to me.

> And I have a board to test with but without any display panel, I'm
> afraid.
> 
> On Thu, Mar 15, 2018 at 03:42:00PM -0700, Dmitry Torokhov wrote:
> > Commit fe79f919f47e ("sh: ecovec24: Use gpio-backlight") removed custom
> > backlight support and switched over to generic gpio-backlight driver. The
> > comment when we run with DVI states "no backlight", but setting
> > gpio_backlight_data.fbdev to NULL actually makes gpio-backlight to react to
> > events from any framebuffer device, not ignore them.
> >
> > We want to get rid of platform data in favor of generic device properties
> > in gpio_backlight driver, so we can not have kernel pointers passed around
> > to tie the framebuffer device to backlight. Assuming that the intent of the
> > above referenced commit was to indeed not export backlight when using DVI,
> > let's switch to conditionally registering backlight device so it is not
> > present at all in DVI case.
> >
> > Signed-off-by: Dmitry Torokhov <dmitry.torokhov@...il.com>
> > ---
> >  arch/sh/boards/mach-ecovec24/setup.c | 24 +++++++++++++++++-------
> >  1 file changed, 17 insertions(+), 7 deletions(-)
> >
> > diff --git a/arch/sh/boards/mach-ecovec24/setup.c b/arch/sh/boards/mach-ecovec24/setup.c
> > index 6f929abe0b50f..67633d2d42390 100644
> > --- a/arch/sh/boards/mach-ecovec24/setup.c
> > +++ b/arch/sh/boards/mach-ecovec24/setup.c
> > @@ -368,7 +368,6 @@ static struct platform_device lcdc_device = {
> >  };
> >
> >  static struct gpio_backlight_platform_data gpio_backlight_data = {
> > -	.fbdev = &lcdc_device.dev,
> >  	.gpio = GPIO_PTR1,
> >  	.def_value = 1,
> >  	.name = "backlight",
> > @@ -987,7 +986,6 @@ static struct platform_device *ecovec_devices[] __initdata = {
> >  	&usb1_common_device,
> >  	&usbhs_device,
> >  	&lcdc_device,
> > -	&gpio_backlight_device,
> >  	&ceu0_device,
> >  	&ceu1_device,
> >  	&keysc_device,
> > @@ -1077,6 +1075,8 @@ static int __init arch_setup(void)
> >  {
> >  	struct clk *clk;
> >  	bool cn12_enabled = false;
> > +	bool use_backlight = false;
> > +	int error;
> >
> >  	/* register board specific self-refresh code */
> >  	sh_mobile_register_self_refresh(SUSP_SH_STANDBY | SUSP_SH_SF |
> > @@ -1193,9 +1193,6 @@ static int __init arch_setup(void)
> >  		lcdc_info.ch[0].lcd_modes		= ecovec_dvi_modes;
> >  		lcdc_info.ch[0].num_modes		= ARRAY_SIZE(ecovec_dvi_modes);
> >
> > -		/* No backlight */
> > -		gpio_backlight_data.fbdev = NULL;
> > -
> >  		gpio_set_value(GPIO_PTA2, 1);
> >  		gpio_set_value(GPIO_PTU1, 1);
> >  	} else {
> > @@ -1217,6 +1214,8 @@ static int __init arch_setup(void)
> >  		/* enable TouchScreen */
> >  		i2c_register_board_info(0, &ts_i2c_clients, 1);
> >  		irq_set_irq_type(IRQ0, IRQ_TYPE_LEVEL_LOW);
> > +
> > +		use_backlight = true;
> >  	}
> >
> >  	/* enable CEU0 */
> > @@ -1431,8 +1430,19 @@ static int __init arch_setup(void)
> >  	gpio_set_value(GPIO_PTG4, 1);
> >  #endif
> >
> > -	return platform_add_devices(ecovec_devices,
> > -				    ARRAY_SIZE(ecovec_devices));
> > +	error = platform_add_devices(ecovec_devices,
> > +				      ARRAY_SIZE(ecovec_devices));
> 
> I would invert this.
> Register the backlight first, then all other devices.

We could do that, but why would that be better?

> 
> 
> > +	if (error)
> > +		return error;
> > +
> > +	if (use_backlight) {
> > +		error = platform_device_add(&gpio_backlight_device);
> > +		if (error)
> > +			pr_warn("%s: failed to register backlight: %d\n",
> > +				error);
> 
> Could you use dev_warn here? Also the format is wrong, I assume you

I would rather not, as the backlight device would be in unknown state
here, and using dev_warn with device that has not been fully registered
does not give any benefits. There is also no ambiguity as there is only
one backlight.

> are missing a '__func__' as second function argument.

I'll fix this.

> 
> Also, you may want to return error.

How would caller handle this error? Should we kill all successfully
registered devices on error adding backlight?

Thanks.

-- 
Dmitry