Re: [PATCH v16 09/10] drm/panel: Use of_find_backlight helper

[Noralf TrÃnnes]

Den 18.01.2018 13.07, skrev Meghana Madhyastha:
> On Tue, Jan 16, 2018 at 06:08:53PM +0100, Noralf TrÃnnes 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@xxxxxxxxx>
> > > ---
> > >   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,
ÂÂÂ ÂÂÂ ÂÂÂ ÂÂÂ Â struct module *owner)
{
...
ÂÂÂ if (drv->probe)
ÂÂÂ ÂÂÂ drv->driver.probe = mipi_dsi_drv_probe;
...
}

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

ÂÂÂ 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)
{
...
ÂÂÂ } else if (drv->probe) {
ÂÂÂ ÂÂÂ ret = drv->probe(dev);
ÂÂÂ ÂÂÂ if (ret)
ÂÂÂ ÂÂÂ ÂÂÂ goto probe_failed;
ÂÂÂ }
...
probe_failed:
...
ÂÂÂ 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:

ÂÂÂÂÂÂÂ 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;