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SubjectRe: [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@gmail.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

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