Hi I am a bit new to Linux and therefore am unable to appreciate exactly the use of various techniques used to map physical memory to user or kernel space. I have come across functions like ioremap(), remap_page_range(), etc. I am still a _bit_ confused as to exactly what to use for our purpose.
I have an MPC8260 target with 128 MB SDRAM (0x00000000 - 0x07FFFFFF), 32 MB FLASH (0xFE000000 - 0xFFFFFFFF). In between, I have some CPLDs and FPGAs mapped at various physical addresses. I wish to access these devices from a user program or from a device driver inserted into the kernel. Please tell me how do I go about it? What I have done right now is to use ioremap() to remap a section of physical memory to kernel virtual memory and try to use it. For example, we have a CPLD whose registers we wish to manipulate. These registers lie in the address range 0x30000000 - 0x300000FF. I map this range as follows: unsigned char *cpld_mem; cpld_mem = (unsigned char *)ioremap(0x30000000, 0x100); Is this correct? After I do this, can I write to and read from the physical memory locations 0x30000000-0x300000FF using writeb() and readb()? Or do I have to use outb() and inb()? Please do clarify my doubts. Also, what is the *highest memory address* as well as *maximum memory size* that I can map to kernel or user space using ioremap()? In other words, can I map any address in the 32-bit address space to kernel virtual space using ioremap()? Also, what chunk size of memory can I map in one go? Please give me some ideas regarding my doubts. I need to get finished with the driver soon. Regards Vijay Padiyar http://www.vijaypadiyar.eu.tf
