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I'm studying on writing embedded linux driver, and decided to fire a few GPIOs to make sure I understand the book (LDD3, chap9.4.1) correctly. I am able to control the correct GPIO pins as intended (making it high and low, I probed with a multimeter); however, I tested 2 pieces of code, one with request_mem_region() , and one without. I'm expecting the one without will fail, but both is working just fine. Code with request_mem_region : if( request_mem_region( PIN3_CONF_PHYS, MAPPED_SIZE_GPIO_CONF,DEVICE_NAME ) == NULL ) { printk( KERN_ALERT "GPIO_140_141_conf_phys error:%s: unable to obtain I/O memory address 0x%08llX\n", DEVICE_NAME, PIN3_CONF_PHYS ); return -EBUSY; } pin3_conf = (u32)ioremap( PIN3_CONF_PHYS, MAPPED_SIZE_GPIO_CONF); pin4_conf = (u32)ioremap( PIN4_CONF_PHYS, MAPPED_SIZE_GPIO_CONF); pin5_conf = (u32)ioremap( PIN5_CONF_PHYS, MAPPED_SIZE_GPIO_CONF); pin6_conf = (u32)ioremap( PIN6_CONF_PHYS, MAPPED_SIZE_GPIO_CONF); //----------------------------------------------------------------- if( request_mem_region( GPIO_BANK5_PHYS, MAPPED_SIZE_GPIO_5,DEVICE_NAME ) == NULL ) { printk( KERN_ALERT "error:%s: unable to obtain I/O memory address 0x%08llX\n", DEVICE_NAME, GPIO_BANK5_PHYS ); return -EBUSY; } gpio_virt = (u32)ioremap( GPIO_BANK5_PHYS, MAPPED_SIZE_GPIO_5 ); //some iowrite32() functions continue... Code without request_mem_region() : pin3_conf = (u32)ioremap( PIN3_CONF_PHYS, MAPPED_SIZE_GPIO_CONF); pin4_conf = (u32)ioremap( PIN4_CONF_PHYS, MAPPED_SIZE_GPIO_CONF); pin5_conf = (u32)ioremap( PIN5_CONF_PHYS, MAPPED_SIZE_GPIO_CONF); pin6_conf = (u32)ioremap( PIN6_CONF_PHYS, MAPPED_SIZE_GPIO_CONF); gpio_virt = (u32)ioremap( GPIO_BANK5_PHYS, MAPPED_SIZE_GPIO_5 ); //some iowrite32() funct

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