# \[PATCH\] backlight: Add of\_find\_backlight\_by\_node() function - Subsystems: FRAMEBUFFER LAYER, BACKLIGHT CLASS/SUBSYSTEM, THE REST - Maintainers: Helge Deller, Lee Jones, Daniel Thompson, Jingoo Han, Linus Torvalds - List: linux-fbdev - 7 messages, 3 authors - Page: https://ratatoskr.run/linux-fbdev/2012/11/3954290/t ## \[PATCH\] backlight: Add of\_find\_backlight\_by\_node() function - From: Thierry Reding \ - Date: 2012-11-09 14:04:57 - Message: https://ratatoskr.run/linux-fbdev/2012/11/3954290.md ```text This function finds the struct backlight_device for a given device tree node. A dummy function is provided so that it safely compiles out if OF support is disabled. Signed-off-by: Thierry Reding --- drivers/video/backlight/backlight.c | 17 +++++++++++++++++ include/linux/backlight.h | 10 ++++++++++ 2 files changed, 27 insertions(+) diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c index 297db2f..0d1ed4f 100644 --- a/drivers/video/backlight/backlight.c +++ b/drivers/video/backlight/backlight.c @@ -370,6 +370,23 @@ void backlight_device_unregister(struct backlight_device *bd) } EXPORT_SYMBOL(backlight_device_unregister); +#if IS_ENABLED(CONFIG_OF) +static int of_parent_match(struct device *dev, void *data) +{ + return dev->parent && dev->parent->of_node = data; +} + +struct backlight_device *of_find_backlight_by_node(struct device_node *node) +{ + struct device *dev; + + dev = class_find_device(backlight_class, NULL, node, of_parent_match); + + return dev ? to_backlight_device(dev) : NULL; +} +EXPORT_SYMBOL(of_find_backlight_by_node); +#endif + static void __exit backlight_class_exit(void) { class_destroy(backlight_class); diff --git a/include/linux/backlight.h b/include/linux/backlight.h index 5ffc6dd..11840e9 100644 --- a/include/linux/backlight.h +++ b/include/linux/backlight.h @@ -134,4 +134,14 @@ struct generic_bl_info { void (*kick_battery)(void); }; +#if IS_ENABLED(CONFIG_OF) +struct backlight_device *of_find_backlight_by_node(struct device_node *node); +#else +static inline struct backlight_device * +of_find_backlight_by_node(struct device_node *node) +{ + return NULL; +} +#endif + #endif -- 1.8.0 ``` ## Re: \[PATCH\] backlight: Add of\_find\_backlight\_by\_node() function - From: Jingoo Han \ - Date: 2012-11-15 01:30:20 - Message: https://ratatoskr.run/linux-fbdev/2012/11/3957107.md ```text On Friday, November 09, 2012 11:05 PM Thierry Reding wrote > > This function finds the struct backlight_device for a given device tree > node. A dummy function is provided so that it safely compiles out if OF > support is disabled. > > Signed-off-by: Thierry Reding CC'ed Andrew Morton Hi Thierry Reding, The patch itself looks good. Could you explain when this API is used? Thank you. Best regards, Jingoo Han > --- > drivers/video/backlight/backlight.c | 17 +++++++++++++++++ > include/linux/backlight.h | 10 ++++++++++ > 2 files changed, 27 insertions(+) > > diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c > index 297db2f..0d1ed4f 100644 > --- a/drivers/video/backlight/backlight.c > +++ b/drivers/video/backlight/backlight.c > @@ -370,6 +370,23 @@ void backlight_device_unregister(struct backlight_device *bd) > } > EXPORT_SYMBOL(backlight_device_unregister); > > +#if IS_ENABLED(CONFIG_OF) > +static int of_parent_match(struct device *dev, void *data) > +{ > + return dev->parent && dev->parent->of_node = data; > +} > + > +struct backlight_device *of_find_backlight_by_node(struct device_node *node) > +{ > + struct device *dev; > + > + dev = class_find_device(backlight_class, NULL, node, of_parent_match); > + > + return dev ? to_backlight_device(dev) : NULL; > +} > +EXPORT_SYMBOL(of_find_backlight_by_node); > +#endif > + > static void __exit backlight_class_exit(void) > { > class_destroy(backlight_class); > diff --git a/include/linux/backlight.h b/include/linux/backlight.h > index 5ffc6dd..11840e9 100644 > --- a/include/linux/backlight.h > +++ b/include/linux/backlight.h > @@ -134,4 +134,14 @@ struct generic_bl_info { > void (*kick_battery)(void); > }; > > +#if IS_ENABLED(CONFIG_OF) > +struct backlight_device *of_find_backlight_by_node(struct device_node *node); > +#else > +static inline struct backlight_device * > +of_find_backlight_by_node(struct device_node *node) > +{ > + return NULL; > +} > +#endif > + > #endif > -- > 1.8.0 > > -- > To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html ``` ## Re: \[PATCH\] backlight: Add of\_find\_backlight\_by\_node() function - From: Thierry Reding \ - Date: 2012-11-15 06:51:48 - Message: https://ratatoskr.run/linux-fbdev/2012/11/3957337.md ```text On Thu, Nov 15, 2012 at 10:30:11AM +0900, Jingoo Han wrote: > On Friday, November 09, 2012 11:05 PM Thierry Reding wrote > > > > This function finds the struct backlight_device for a given device tree > > node. A dummy function is provided so that it safely compiles out if OF > > support is disabled. > > > > Signed-off-by: Thierry Reding > > CC'ed Andrew Morton Yes, the backlight subsystem isn't very well maintained, so I should have added Andrew in the first place. Thanks. > > Hi Thierry Reding, > > The patch itself looks good. > Could you explain when this API is used? > Thank you. I use this for the upcoming Tegra DRM driver in order to hook up the backlight with the DRM driver via DT to allow switching off the backlight when the corresponding DRM output is switched of using DPMS. Basically what you have is something like this in the device tree: display { ... backlight = <&backlight>; ... } Then you call something along these lines: np = of_parse_phandle(display, "backlight", 0); if (np) { backlight = of_find_backlight_by_node(np); of_node_put(np); } And then use the standard backlight API on the returned pointer. Thierry ``` ## Re: \[PATCH\] backlight: Add of\_find\_backlight\_by\_node() function - From: Jingoo Han \ - Date: 2012-11-15 08:58:40 - Message: https://ratatoskr.run/linux-fbdev/2012/11/3957433.md ```text On Thursday, November 15, 2012 3:52 PM Thierry Reding wrote > On Thu, Nov 15, 2012 at 10:30:11AM +0900, Jingoo Han wrote: > > On Friday, November 09, 2012 11:05 PM Thierry Reding wrote > > > > > > This function finds the struct backlight_device for a given device tree > > > node. A dummy function is provided so that it safely compiles out if OF > > > support is disabled. > > > > > > Signed-off-by: Thierry Reding > > > > CC'ed Andrew Morton > > Yes, the backlight subsystem isn't very well maintained, so I should > have added Andrew in the first place. Thanks. > > > > > Hi Thierry Reding, > > > > The patch itself looks good. > > Could you explain when this API is used? > > Thank you. > > I use this for the upcoming Tegra DRM driver in order to hook up the > backlight with the DRM driver via DT to allow switching off the > backlight when the corresponding DRM output is switched of using DPMS. > Basically what you have is something like this in the device tree: > > display { > ... > > backlight = <&backlight>; > > ... > } > > Then you call something along these lines: > > np = of_parse_phandle(display, "backlight", 0); > if (np) { > backlight = of_find_backlight_by_node(np); > of_node_put(np); > } > > And then use the standard backlight API on the returned pointer. OK, I see how this API can be called. AS you mentioned, it will allow Tegra DRM driver to use the backlight driver. Acked-by: Jingoo Han Best regards, Jingoo Han > > Thierry ``` ## Re: \[PATCH\] backlight: Add of\_find\_backlight\_by\_node() function - From: Thierry Reding \ - Date: 2012-11-16 20:56:48 - Message: https://ratatoskr.run/linux-fbdev/2012/11/3958539.md ```text On Thu, Nov 15, 2012 at 05:58:35PM +0900, Jingoo Han wrote: > On Thursday, November 15, 2012 3:52 PM Thierry Reding wrote > > On Thu, Nov 15, 2012 at 10:30:11AM +0900, Jingoo Han wrote: > > > On Friday, November 09, 2012 11:05 PM Thierry Reding wrote > > > > > > > > This function finds the struct backlight_device for a given device tree > > > > node. A dummy function is provided so that it safely compiles out if OF > > > > support is disabled. > > > > > > > > Signed-off-by: Thierry Reding > > > > > > CC'ed Andrew Morton > > > > Yes, the backlight subsystem isn't very well maintained, so I should > > have added Andrew in the first place. Thanks. > > > > > > > > Hi Thierry Reding, > > > > > > The patch itself looks good. > > > Could you explain when this API is used? > > > Thank you. > > > > I use this for the upcoming Tegra DRM driver in order to hook up the > > backlight with the DRM driver via DT to allow switching off the > > backlight when the corresponding DRM output is switched of using DPMS. > > Basically what you have is something like this in the device tree: > > > > display { > > ... > > > > backlight = <&backlight>; > > > > ... > > } > > > > Then you call something along these lines: > > > > np = of_parse_phandle(display, "backlight", 0); > > if (np) { > > backlight = of_find_backlight_by_node(np); > > of_node_put(np); > > } > > > > And then use the standard backlight API on the returned pointer. > > OK, I see how this API can be called. > AS you mentioned, it will allow Tegra DRM driver to use > the backlight driver. > > Acked-by: Jingoo Han Andrew, any chance we could still get this in for the 3.8 merge window? Thierry ``` ## Re: \[PATCH\] backlight: Add of\_find\_backlight\_by\_node() function - From: Andrew Morton \ - Date: 2012-11-16 21:16:48 - Message: https://ratatoskr.run/linux-fbdev/2012/11/3958544.md ```text On Fri, 9 Nov 2012 15:04:38 +0100 Thierry Reding [ref] wrote: > This function finds the struct backlight_device for a given device tree > node. A dummy function is provided so that it safely compiles out if OF > support is disabled. > > Signed-off-by: Thierry Reding > --- > drivers/video/backlight/backlight.c | 17 +++++++++++++++++ > include/linux/backlight.h | 10 ++++++++++ > 2 files changed, 27 insertions(+) > > diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c > index 297db2f..0d1ed4f 100644 > --- a/drivers/video/backlight/backlight.c > +++ b/drivers/video/backlight/backlight.c > @@ -370,6 +370,23 @@ void backlight_device_unregister(struct backlight_device *bd) > } > EXPORT_SYMBOL(backlight_device_unregister); > > +#if IS_ENABLED(CONFIG_OF) Using IS_ENABLED() was odd. We'll never support CONFIG_OF=m, so can't we use plain old "#ifdef CONFIG_OF" here? --- a/drivers/video/backlight/backlight.c~backlight-add-of_find_backlight_by_node-function-fix +++ a/drivers/video/backlight/backlight.c @@ -370,7 +370,7 @@ void backlight_device_unregister(struct } EXPORT_SYMBOL(backlight_device_unregister); -#if IS_ENABLED(CONFIG_OF) +#ifdef CONFIG_OF static int of_parent_match(struct device *dev, void *data) { return dev->parent && dev->parent->of_node = data; --- a/include/linux/backlight.h~backlight-add-of_find_backlight_by_node-function-fix +++ a/include/linux/backlight.h @@ -134,7 +134,7 @@ struct generic_bl_info { void (*kick_battery)(void); }; -#if IS_ENABLED(CONFIG_OF) +#ifdef CONFIG_OF struct backlight_device *of_find_backlight_by_node(struct device_node *node); #else static inline struct backlight_device * _ > +static int of_parent_match(struct device *dev, void *data) > +{ > + return dev->parent && dev->parent->of_node = data; > +} > + > +struct backlight_device *of_find_backlight_by_node(struct device_node *node) > +{ > + struct device *dev; > + > + dev = class_find_device(backlight_class, NULL, node, of_parent_match); > + > + return dev ? to_backlight_device(dev) : NULL; > +} > +EXPORT_SYMBOL(of_find_backlight_by_node); It's a global, exported-to-modules function. We should document such major interfaces. Unless they are dead trivial, but I don't think this one is that simple. The semantics of the return value could be explained, and callers should be told that of_find_backlight_by_node() took a ref on the returned device, and that they need to run put_device(retval->dev), if retval was not NULL. And anything else which might be useful. ``` ## Re: \[PATCH\] backlight: Add of\_find\_backlight\_by\_node() function - From: Thierry Reding \ - Date: 2012-11-16 21:34:28 - Message: https://ratatoskr.run/linux-fbdev/2012/11/3958548.md ```text On Fri, Nov 16, 2012 at 01:16:45PM -0800, Andrew Morton wrote: > On Fri, 9 Nov 2012 15:04:38 +0100 > Thierry Reding [ref] wrote: > > > This function finds the struct backlight_device for a given device tree > > node. A dummy function is provided so that it safely compiles out if OF > > support is disabled. > > > > Signed-off-by: Thierry Reding > > --- > > drivers/video/backlight/backlight.c | 17 +++++++++++++++++ > > include/linux/backlight.h | 10 ++++++++++ > > 2 files changed, 27 insertions(+) > > > > diff --git a/drivers/video/backlight/backlight.c b/drivers/video/backlight/backlight.c > > index 297db2f..0d1ed4f 100644 > > --- a/drivers/video/backlight/backlight.c > > +++ b/drivers/video/backlight/backlight.c > > @@ -370,6 +370,23 @@ void backlight_device_unregister(struct backlight_device *bd) > > } > > EXPORT_SYMBOL(backlight_device_unregister); > > > > +#if IS_ENABLED(CONFIG_OF) > > Using IS_ENABLED() was odd. We'll never support CONFIG_OF=m, so can't > we use plain old "#ifdef CONFIG_OF" here? > > --- a/drivers/video/backlight/backlight.c~backlight-add-of_find_backlight_by_node-function-fix > +++ a/drivers/video/backlight/backlight.c > @@ -370,7 +370,7 @@ void backlight_device_unregister(struct > } > EXPORT_SYMBOL(backlight_device_unregister); > > -#if IS_ENABLED(CONFIG_OF) > +#ifdef CONFIG_OF > static int of_parent_match(struct device *dev, void *data) > { > return dev->parent && dev->parent->of_node == data; > --- a/include/linux/backlight.h~backlight-add-of_find_backlight_by_node-function-fix > +++ a/include/linux/backlight.h > @@ -134,7 +134,7 @@ struct generic_bl_info { > void (*kick_battery)(void); > }; > > -#if IS_ENABLED(CONFIG_OF) > +#ifdef CONFIG_OF > struct backlight_device *of_find_backlight_by_node(struct device_node *node); > #else > static inline struct backlight_device * > _ Yes, that should work. > > +static int of_parent_match(struct device *dev, void *data) > > +{ > > + return dev->parent && dev->parent->of_node == data; > > +} > > + > > +struct backlight_device *of_find_backlight_by_node(struct device_node *node) > > +{ > > + struct device *dev; > > + > > + dev = class_find_device(backlight_class, NULL, node, of_parent_match); > > + > > + return dev ? to_backlight_device(dev) : NULL; > > +} > > +EXPORT_SYMBOL(of_find_backlight_by_node); > > It's a global, exported-to-modules function. We should document such > major interfaces. Unless they are dead trivial, but I don't think this > one is that simple. The semantics of the return value could be > explained, and callers should be told that of_find_backlight_by_node() > took a ref on the returned device, and that they need to run > put_device(retval->dev), if retval was not NULL. > > And anything else which might be useful. Yes, I should have thought about that. I'll add some proper kerneldoc and repost. Thanks for reviewing, Thierry ```