During my work in device drivers, I came to know that of_match_table() is to point the tuple of compatibility strings.
However, I couldn't find the importance of of_match_ptr().
1 Answer
of_match_ptr() is a preprocessor macro defined in include/linux/of.h:
#ifdef CONFIG_OF #define of_match_ptr(_ptr) (_ptr) #else /* CONFIG_OF */ #define of_match_ptr(_ptr) NULL #endif /* CONFIG_OF */ When the kernel is compiled with Device Tree and Open Firmware support, i.e. CONFIG_OF=y it will result in the passed pointer. Otherwise it will yield NULL.
Using the macro instead of directly passing the pointer, is to guard the of_match_table member. There are bus drivers which check of_match_table for NULL to not dereference an invalid pointer.
However, many drivers are compiled in-tree with a compile switch defined in their corresponding Kconfig that already depends on CONFIG_OF. For example, the compile switch of a driver for analog device ADV748X video decoder has this dependency:
config VIDEO_ADV748X tristate "Analog Devices ADV748x decoder" depends on VIDEO_V4L2 && I2C depends on OF select MEDIA_CONTROLLER select VIDEO_V4L2_SUBDEV_API select REGMAP_I2C select V4L2_FWNODE help V4L2 subdevice driver for the Analog Devices ADV7481 and ADV7482 HDMI/Analog video decoders. To compile this driver as a module, choose M here: the module will be called adv748x. and omits the macro in drivers/media/i2c/adv748x/adv748x-core.c:
static struct i2c_driver adv748x_driver = { .driver = { .name = "adv748x", .of_match_table = adv748x_of_table, .pm = &adv748x_pm_ops, }, .probe_new = adv748x_probe, .remove = adv748x_remove, }; 
