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Subject: Re: [RFC 2/4] sh: ecovec24: conditionally register backlight device
From:   John Paul Adrian Glaubitz <glaubitz@physik.fu-berlin.de>
In-Reply-To: <20180317092516.g5p5ybka57abyhex@apu3b>
Date:   Sat, 17 Mar 2018 19:21:17 +0900
Cc:     Dmitry Torokhov <dmitry.torokhov@gmail.com>,
        Laurent Pinchart <laurent.pinchart@ideasonboard.com>,
        Lee Jones <lee.jones@linaro.org>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        Jingoo Han <jingoohan1@gmail.com>, linux-fbdev@vger.kernel.org,
        linux-kernel@vger.kernel.org, linux-sh@vger.kernel.org,
        Yoshinori Sato <ysato@users.sourceforge.jp>,
        Rich Felker <dalias@libc.org>,
        Linus Walleij <linus.walleij@linaro.org>
Content-Transfer-Encoding: 8BIT
Message-Id: <02834805-5053-4BDC-9256-DF1AFFEC8630@physik.fu-berlin.de>
References: <20180315224202.96668-1-dmitry.torokhov@gmail.com> <20180315224202.96668-3-dmitry.torokhov@gmail.com> <20180316100748.GH16424@w540> <20180316233800.GA32310@dtor-ws> <20180317092516.g5p5ybka57abyhex@apu3b>
To:     jacopo mondi <jacopo@jmondi.org>
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk


> On Mar 17, 2018, at 6:25 PM, jacopo mondi <jacopo@jmondi.org> wrote:
> 
> Hi Dmitry,
> 
>> On Fri, Mar 16, 2018 at 04:38:00PM -0700, Dmitry Torokhov wrote:
>> 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.
> 
> Yes, it is a SuperH 4 based development board. It is old for sure. I'm
> also working on removing some stuff the ecovec board file is the only
> user of...

Umh, but I’m still using the SH7724 Evovec board. Please don’t remove support for that.

The SuperH port of the Linux kernel is still maintained.

Adrian

> 
>>> 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?
>> 
> 
> That if backlight device registration fails we do not register all
> other devices. But yes that may be a bit too harsh, isn't it?
> 
>>> 
>>> 
>>>> +    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.
> 
> You are very correct, sorry for the fuss.
> 
>> 
>>> 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?
> 
> As the function returned an error code for 'platform_add_devices()' I
> thought we may want to return one as well. That's why I proposed to
> invert the registration order :)
> 
> All minor nits btw,  sorry for jumping up, I understand this is an
> RFC and ecovec board file is not the real juice of this series ;)
> 
> Ping me if I can help with testing as I've the board.
> 
> Thanks
>   j
> 
>> 
>> Thanks.
>> 
>> -- 
>> Dmitry
> --
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