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Subject: Re: [PATCH v16 09/10] drm/panel: Use of_find_backlight helper
To:     Meghana Madhyastha <meghana.madhyastha@gmail.com>,
        Lee Jones <lee.jones@linaro.org>,
        Daniel Thompson <daniel.thompson@linaro.org>,
        Jingoo Han <jingoohan1@gmail.com>,
        Thierry Reding <thierry.reding@gmail.com>,
        Tomi Valkeinen <tomi.valkeinen@ti.com>,
        Daniel Vetter <daniel.vetter@intel.com>,
        Sean Paul <seanpaul@chromium.org>,
        dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
References: <cover.1516098341.git.meghana.madhyastha@gmail.com>
 <d44db943ccd6680c060060b263b2ec8c44e9ff1b.1516098341.git.meghana.madhyastha@gmail.com>
 <af25028c-8134-8178-d3fa-2cb76baaf3aa@tronnes.org>
 <20180118120732.GC4864@meghana-HP-Pavilion-Notebook>
From:   =?UTF-8?Q?Noralf_Tr=c3=b8nnes?= <noralf@tronnes.org>
Message-ID: <938045f6-e404-b26e-138b-7eb5ef456975@tronnes.org>
Date:   Thu, 18 Jan 2018 15:51:12 +0100
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Den 18.01.2018 13.07, skrev Meghana Madhyastha:
> On Tue, Jan 16, 2018 at 06:08:53PM +0100, Noralf Trønnes wrote:
>> Den 16.01.2018 11.36, skrev Meghana Madhyastha:
>>> Replace of_find_backlight_by_node and of the code around it
>>> with of_find_backlight helper to avoid repetition of code.
>>>
>>> Signed-off-by: Meghana Madhyastha <meghana.madhyastha@gmail.com>
>>> ---
>>>   drivers/gpu/drm/panel/panel-innolux-p079zca.c   | 10 +++-------
>>>   drivers/gpu/drm/panel/panel-sharp-lq101r1sx01.c | 10 +++-------
>>>   drivers/gpu/drm/panel/panel-sharp-ls043t1le01.c | 10 +++-------
>>>   3 files changed, 9 insertions(+), 21 deletions(-)
>>>
>>> diff --git a/drivers/gpu/drm/panel/panel-innolux-p079zca.c b/drivers/gpu/drm/panel/panel-innolux-p079zca.c
>>> index 4c1b29eec..a69b0530f 100644
>>> --- a/drivers/gpu/drm/panel/panel-innolux-p079zca.c
>>> +++ b/drivers/gpu/drm/panel/panel-innolux-p079zca.c
>>> @@ -230,14 +230,10 @@ static int innolux_panel_add(struct innolux_panel *innolux)
>>>   		innolux->enable_gpio = NULL;
>>>   	}
>>> -	np = of_parse_phandle(dev->of_node, "backlight", 0);
>>> -	if (np) {
>>> -		innolux->backlight = of_find_backlight_by_node(np);
>>> -		of_node_put(np);
>>> +	innolux->backlight = devm_of_find_backlight(np);
>> This driver isn't broken like tinydrm was, so it does put the backlight
>> device on cleanup like it should. So when you're using the devm_ version,
>> the result is a double put. Just remove the put_device() in
>> innolux_panel_add/del() and you're good.
> I have a quick question here. So devm_of_find_backlight automatically
> does a put_device on detachment of the driver. However in this case,
> put_device is called when panel_add is not successful (i.e when it
> returns a negative value here). So is devm's release mechanism still
> invoked here ?

As long as the error is propagated back up the chain, which it is in this
case, devres_release_all() is called and the resources are released.

Driver callchain passing up the error:
innolux_panel_driver.probe = innolux_panel_probe <- innolux_panel_add <- 
devm_of_find_backlight

This is mipi_dsi setting up the probe hook and calling into it's own 
version:

drivers/gpu/drm/drm_mipi_dsi.c:
int mipi_dsi_driver_register_full(struct mipi_dsi_driver *drv,
                   struct module *owner)
{
...
     if (drv->probe)
         drv->driver.probe = mipi_dsi_drv_probe;
...
}

static int mipi_dsi_drv_probe(struct device *dev)
{
     struct mipi_dsi_driver *drv = to_mipi_dsi_driver(dev->driver);
     struct mipi_dsi_device *dsi = to_mipi_dsi_device(dev);

     return drv->probe(dsi);
}

This is the device-driver core that initiates the probing:

drivers/base/dd.c
static int really_probe(struct device *dev, struct device_driver *drv)
{
...
     } else if (drv->probe) {
         ret = drv->probe(dev);
         if (ret)
             goto probe_failed;
     }
...
probe_failed:
...
     devres_release_all(dev);
...
}

> 	err = drm_panel_add(&innolux->base);
> 	if (err < 0)
> 		goto put_backlight;
>
> 	return 0;
>
> 	put_backlight:
> 		put_device(&innolux->backlight->dev);
> 	return err;
>
> If so then I should change this to
> 	err = drm_panel_add(&innolux->base)
> 	return err;

Yes, and you can drop the variable:

         return drm_panel_add(&innolux->base);

Noralf.

>
> Thanks and regards,
> Meghana
>
>> I haven't checked the other drivers.
>>
>> Noralf.
>>
>> PS:
>> Give people a few days (one week?) to respond before respinning a new
>> version, so we avoid a fragmented discussion.
>>
>>> -		if (!innolux->backlight)
>>> -			return -EPROBE_DEFER;
>>> -	}
>>> +	if (IS_ERR(innolux->backlight))
>>> +		return PTR_ERR(innolux->backlight);
>>>   	drm_panel_init(&innolux->base);
>>>   	innolux->base.funcs = &innolux_panel_funcs;
>>> diff --git a/drivers/gpu/drm/panel/panel-sharp-lq101r1sx01.c b/drivers/gpu/drm/panel/panel-sharp-lq101r1sx01.c
>>> index 1512ec4f3..d5450c9d9 100644
>>> --- a/drivers/gpu/drm/panel/panel-sharp-lq101r1sx01.c
>>> +++ b/drivers/gpu/drm/panel/panel-sharp-lq101r1sx01.c
>>> @@ -329,14 +329,10 @@ static int sharp_panel_add(struct sharp_panel *sharp)
>>>   	if (IS_ERR(sharp->supply))
>>>   		return PTR_ERR(sharp->supply);
>>> -	np = of_parse_phandle(sharp->link1->dev.of_node, "backlight", 0);
>>> -	if (np) {
>>> -		sharp->backlight = of_find_backlight_by_node(np);
>>> -		of_node_put(np);
>>> +	sharp->backlight = devm_of_find_backlight(np);
>>> -		if (!sharp->backlight)
>>> -			return -EPROBE_DEFER;
>>> -	}
>>> +	if (IS_ERR(sharp->backlight))
>>> +		return PTR_ERR(sharp->backlight);
>>>   	drm_panel_init(&sharp->base);
>>>   	sharp->base.funcs = &sharp_panel_funcs;
>>> diff --git a/drivers/gpu/drm/panel/panel-sharp-ls043t1le01.c b/drivers/gpu/drm/panel/panel-sharp-ls043t1le01.c
>>> index a6af3257f..db31d8268 100644
>>> --- a/drivers/gpu/drm/panel/panel-sharp-ls043t1le01.c
>>> +++ b/drivers/gpu/drm/panel/panel-sharp-ls043t1le01.c
>>> @@ -273,14 +273,10 @@ static int sharp_nt_panel_add(struct sharp_nt_panel *sharp_nt)
>>>   		gpiod_set_value(sharp_nt->reset_gpio, 0);
>>>   	}
>>> -	np = of_parse_phandle(dev->of_node, "backlight", 0);
>>> -	if (np) {
>>> -		sharp_nt->backlight = of_find_backlight_by_node(np);
>>> -		of_node_put(np);
>>> +	sharp_nt->backlight = devm_of_find_backlight(np);
>>> -		if (!sharp_nt->backlight)
>>> -			return -EPROBE_DEFER;
>>> -	}
>>> +	if (IS_ERR(sharp_nt->backlight))
>>> +		return PTR_ERR(sharp_nt->backlight);
>>>   	drm_panel_init(&sharp_nt->base);
>>>   	sharp_nt->base.funcs = &sharp_nt_panel_funcs;