[PATCH] drm/panel-simple: take i2c adapter module reference

[PATCH] drm/panel-simple: take i2c adapter module reference

[Johan Hovold]

The i2c subsystem currently blocks during adapter deregistration
whenever there are consumers holding a reference.

Switch to using of_get_i2c_adapter_by_node() which also takes a
reference to the adapter module so that an attempt to unload the module
while in use fails gracefully instead of blocking uninterruptibly.

Signed-off-by: Johan Hovold <johan@kernel.org>
---
 drivers/gpu/drm/panel/panel-simple.c | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
index c09bf3db5e78..f58e83aa4ebe 100644
--- a/drivers/gpu/drm/panel/panel-simple.c
+++ b/drivers/gpu/drm/panel/panel-simple.c
@@ -701,7 +701,7 @@ static struct panel_simple *panel_simple_probe(struct device *dev)
 
 	ddc = of_parse_phandle(dev->of_node, "ddc-i2c-bus", 0);
 	if (ddc) {
-		panel->ddc = of_find_i2c_adapter_by_node(ddc);
+		panel->ddc = of_get_i2c_adapter_by_node(ddc);
 		of_node_put(ddc);
 
 		if (!panel->ddc)
@@ -746,7 +746,7 @@ static struct panel_simple *panel_simple_probe(struct device *dev)
 	pm_runtime_disable(dev);
 free_ddc:
 	if (panel->ddc)
-		put_device(&panel->ddc->dev);
+		i2c_put_adapter(panel->ddc);
 
 	return ERR_PTR(err);
 }
@@ -791,7 +791,7 @@ static void panel_simple_remove(struct device *dev)
 	pm_runtime_dont_use_autosuspend(dev);
 	pm_runtime_disable(dev);
 	if (panel->ddc)
-		put_device(&panel->ddc->dev);
+		i2c_put_adapter(panel->ddc);
 }
 
 static const struct drm_display_mode ampire_am_1280800n3tzqw_t00h_mode = {
-- 
2.54.0

Re: [PATCH] drm/panel-simple: take i2c adapter module reference

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:
- [Low] Calling `i2c_put_adapter()` breaks the build when `CONFIG_I2C` is not enabled.
--

--- Patch [1]: [PATCH] drm/panel-simple: take i2c adapter module reference ---
commit 78f8d3d7539288c8e1940d04e2aff6503a3592b4
Author: Johan Hovold <johan@kernel.org>

drm/panel-simple: take i2c adapter module reference

This patch changes the panel-simple driver to use of_get_i2c_adapter_by_node()
instead of of_find_i2c_adapter_by_node(). This ensures the i2c adapter module
reference is taken, preventing uninterruptible blocking during deregistration.
The teardown paths are updated to use i2c_put_adapter() instead of put_device().

> diff --git a/drivers/gpu/drm/panel/panel-simple.c b/drivers/gpu/drm/panel/panel-simple.c
> index 5c169fdf265c1..79bd6bbec7bde 100644
> --- a/drivers/gpu/drm/panel/panel-simple.c
> +++ b/drivers/gpu/drm/panel/panel-simple.c

[ ... ]

> @@ -746,7 +746,7 @@ static struct panel_simple *panel_simple_probe(struct device *dev)
>  	pm_runtime_disable(dev);
>  free_ddc:
>  	if (panel->ddc)
> -		put_device(&panel->ddc->dev);
> +		i2c_put_adapter(panel->ddc);

[Severity: Low]
Does this cause a build failure when CONFIG_I2C is disabled?

Looking at include/linux/i2c.h, it appears the declaration for i2c_put_adapter()
is guarded by IS_ENABLED(CONFIG_I2C), but there is no corresponding empty stub
provided in the fallback block for when I2C is disabled.

Since this driver can be built without CONFIG_I2C, calling i2c_put_adapter()
unconditionally here in panel_simple_probe() might result in an undefined
reference during linking or an implicit declaration error.

>  
>  	return ERR_PTR(err);
>  }

[ ... ]

> @@ -791,7 +791,7 @@ static void panel_simple_remove(struct device *dev)
>  	pm_runtime_dont_use_autosuspend(dev);
>  	pm_runtime_disable(dev);
>  	if (panel->ddc)
> -		put_device(&panel->ddc->dev);
> +		i2c_put_adapter(panel->ddc);

[Severity: Low]
The same potential build issue with CONFIG_I2C=n applies here in
panel_simple_remove().

>  }
>  
>  static const struct drm_display_mode ampire_am_1280800n3tzqw_t00h_mode = {

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260716132334.1565183-1-johan@kernel.org?part=1