Add an LED driver example using GPIO #290
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jeremy90307
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examples/led.c
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| /* The major device number. We can not rely on dynamic registration | ||
| * any more. | ||
| */ | ||
| #define MAJOR_NUM 100 |
examples/led.c
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| { | ||
| pr_info("device_open(%p)\n", file); | ||
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| try_module_get(THIS_MODULE); |
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See if try_module_get is required or not.
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I have noticed this issue, such as issue #52, and there are still several examples using it. Let me fix it.
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If we want to remove try_module_get, we also need to stop using register_chrdev and use cdev_init and cdev_add instead.
Because with register_chrdev, we need to manually increase or decrease the module's reference count.
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The try_module_get() function should generally be avoided. The only legitimate use case is when you need to reference another module before interacting with it, such as in file operations code. While try_module_get(THIS_MODULE) appears multiple times in the kernel source code, these instances are typically bugs that need to be fixed rather than examples to follow.
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In my modified code, register_chrdev is not included. Should I use the preprocessor to make the changes?
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Because I saw that cdev already appeared in Linux v2.6.
Use GPIO to control LED on/off and add related GPIO knowledge. Test detail: - Tested on Raspberry Pi 5B with Raspberry Pi OS (Debian 12, Linux version 6.12.1-v8-16k+) - Verify that LED example compiles and loads successfully - Verify that LED turns on and off sucessfully
Add an LED driver example using GPIO and add related knowledge.
Test detail:
Tested on Raspberry Pi 5B with Raspberry Pi OS (Debian 12, Linux version 6.12.1-v8-16k+)
Verify that LED sample compiles and loads successfully
Verify that LED turns on and off sucessfully