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Questions tagged [ioremap]

`ioremap()` maps bus memory into CPU space for memory mapped I/O in the Linux kernel

void __iomem *ioremap(unsigned long port, unsigned long size) is the function in the Linux kernel that maps bus memory into CPU space. It will perform a platform specific sequence of operations to make bus memory CPU accessible via the read{b,w,l} write{b,w,l} functions and the other memory mapped I/O helper functions. The returned address is not guaranteed to be usable directly as a virtual address.

Cache behavior through the newly established mapping could be one of but are not limited to:

  • Uncached
  • Write-back
  • Write Combining

References

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Why shouldn't I use ioremap on system memory for ARMv6+?

I need to reserve a large buffer of physically contiguous RAM from the kernel and be able to gaurantee that the buffer will always use a specific, hard-coded physical address. This buffer should remain reserved for the kernel's entire lifetime. I…
Woodrow Barlow
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What is meant by holes in the memory Linux?

I have come across a term - holes in the memory in Linux. I believe this is the memory that is I/O remapped. Is my understanding correct?
dexterous
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Using writel to write 4 bit to ioremap-ed memory address

I'm new to kernel programming, and now trying to write some values to a 32-bit GPIO register in a device driver. The I/O is ioremap()-ed to a memory address. The problem is, I don't know how writel()/writeb()/writew() writes bits to the…
Chung Lun Yuen
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map reserver memory at boot to user space using remap_pfn_range

I am trying to map reserved memory (30M with offset of 2G) at boot time (boot kernel parameters mem=2G memmap=30M$2G) to user space using the remap_pfn_range, bellow is my driver code: #include #include #include…
Mondher123
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Unexpected changes in data written to a physical memory address

The platform is MIPS, and the kernel is linux 2.6.31. First, I reserve 8M RAM zone, out of total RAM of 64M, so the kernel only uses 56M RAM zone. Second, I use the ioremap() function to transform the physical address to a virtual address in kernel,…
dovelj
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Kernel driver, ioremap necessary in MMU-less system?

So, I am a total newbie when it comes to kernel drivers and have a question regarding ioremap function. I am writing a driver for accessing some registers defined in a custom VHDL-module on a SoC with a ARM Cortex-M3 and FPGA fabric. Looking at…
user3077663
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Why we can directly access only the 640k-1MB area in a PCI physical addresses?

http://www.mjmwired.net/kernel/Documentation/IO-mapping.txt 153 - remapping and writing: 154 /* 155 * remap framebuffer PCI memory area at 0xFC000000, 156 * size 1MB, so that we can access it: We can directly 157 * access only…
0x90
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How does PCIe Endpoint device memory is mapped into the systems memory map (MMIO)?

How does Linux Kernel or BIOS map the PCIe endpoint device memory into systems MMIO space ? Is there any API to achieve it ? Lets assume that when writing a Linux device driver for a PCIe endpoint device, How can we map PCIe device memory into MMIO…
Usr1
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Using physical address as sk_buff data fragment

Is it possible to map physical address as data fragment in sk_buff? I am working on Zynq Ultrascale+ platform (FPGA + ARM SOC). I have memory buffer mapped to physical address. The goal is to efficiently send that data over UDP. By efficiently I…
modimo
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LINUX KERNEL driver hangs/freeze after handling mapped register

I'm completely new developing in LINUX kernel, and I'm having some problems in a new LINUX driver I'm developing. After I map NXP PWM registers using ioremap()/ioremap_nocache() and then I try to write to the register mappend my system…
Jonathan Guizar
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What is the effect of using ioremap on physical address already ioremapped by a driver?

I am trying to use the ARM watchdog thorough kernel space. I have a watchdog driver which is statically built and deployed in the kernel. The memory remapped by the driver is seen in /proc/iomem. cat /proc/iomem | grep wdt ff567000-ff567018 :…
nishad kamdar
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list ioremap() mapped addresses in Kernel

As you might know it is possible to list all the mapped physical addresses and their respected virtual addresses for user space applications using /proc/$pid/maps Is there any way to do the same and find virtual addresses of all mapped physical…
Sama Azari
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ioremap - Unable to handle kernel paging request at virtual address XXXXXXXX

I am attempting to access a given memory-region on an am335x-processor in Linux. The idea is to first designate physical addresses, then access said addresses using ioremap. I have been googling the issue for some time, but cannot seem to find any…
Tom
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Is the second parameter in ioremap() gives the size in number of bits for a register- Linux?

My NEC microcontroller has a timer controller register 8-bits - Do, I need to pass 8 in the second parameter of ioremap? After reading the spec, I got to know the following property of it. Address |Function Register Name |Symbol |R/W…
dexterous
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what is the meaning of mapping virtual address to physical address?

I am using "ioremap" to map the address of a GPIO port in the datasheet of Ti AM3359 . The code is running fine. Problem: 1> The problem is , why do we need to map the virtual address to physical address? Is it because physical address is the…
Virendra Kumar
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