On Sat, Sep 13, 2014 at 2:01 PM, Miles MH Chen <orca.chen@gmail.com> wrote:

Hi,

Do you know the value of PHYS_OFFSET of your platform? PHYS_OFFSET defines the starting physical address of your DRAM.

physical address = kmalloc'ed address - PAGE_OFFSET + PHYS_OFFSET

MH

On Sat, Sep 13, 2014 at 4:02 PM, mind entropy <mindentropy@gmail.com> wrote:

...

Hi,

I want to know the physical address [just for debugging and info.Not for DMA etc] of a particular virtual address allocated via kmalloc.

I am running the below code on S3C2440 with 64MB of RAM. The /proc/meminfo returns

MemTotal: 59164 kB MemFree: 35884 kB MemAvailable: 47148 kB

I run the following module for printing the addresses. [This module is only for test. So excuse if I have cut corners].

------------------------------------------------

#include <linux/init.h> #include <linux/kernel.h> #include <linux/printk.h> #include <linux/module.h> #include <linux/gfp.h> #include <linux/types.h> #include <linux/mm.h> #include <linux/mm_types.h> #include <linux/slab.h>

static int vm_mem_test_init(void) {

void *km;

printk(KERN_ALERT "vm mem test init\n");

km = kmalloc(1,GFP_KERNEL);

if(km == NULL) { printk(KERN_ALERT "Could not kmalloc\n"); return -1; } else { printk(KERN_ALERT "Allocated\n"); printk(KERN_ALERT "Virtual addr : %x\n",(unsigned int)km); printk(KERN_ALERT "Kernel physical addr : 0x%x\n",virt_to_phys(km)); kfree(km); }

return 0;

}

The output for the following is:

Virtual addr : c2c080e0 Kernel physical addr : 0x32c080e0

-----------------------------------------------------------

The kernel physical address is wrong as I only have 64MB. Should I be doing a kernel page table walk to get the associated physical address?

Thanks Gautam.

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Miles, I tried printing it. The output is as follows: Kernel physical addr : 0x32d01fe0 Platform phys offset : 0x30000000 Page offset : 0xc0553fb4 The S3C2440 is an ARM9TDMI processor. -Gautam.

On Sat, Sep 13, 2014 at 7:13 PM, Miles MH Chen <orca.chen@gmail.com> wrote:

Kernel physical addr : 0x32d01fe0 Platform phys offset : 0x30000000 Page offset : 0xc0553fb4

The page offset looks weird, since 32bit kernel has 2/2 or 3/1 or 1/3 user/kernel virtual address split. It is not reasonable to have 0xc0553fb4 as page offset. You should c0000000 for 3/1 split.

My fault. I had done "0x%llx" in printk. Now I just did a %x and it shows as 0xc0000000. -Gautam.

Thanks. It set a byte in RAM and checked it using md.b in u-boot. -Gautam. On Sat, Sep 13, 2014 at 10:20 PM, Miles MH Chen <orca.chen@gmail.com> wrote:

ok, now we can say the virt_to_phys returns a correct physical address. 0x32d01fe0. It is a physical address, not a simple offset in dram. Your 64Mb dram has physical address within 0x30000000 ~ 0x34000000.

MH

2014/9/13 下午9:52 於 "mind entropy" <mindentropy@gmail.com> 寫道：

...

On Sat, Sep 13, 2014 at 7:13 PM, Miles MH Chen <orca.chen@gmail.com> wrote:

...

Kernel physical addr : 0x32d01fe0 Platform phys offset : 0x30000000 Page offset : 0xc0553fb4

The page offset looks weird, since 32bit kernel has 2/2 or 3/1 or 1/3 user/kernel virtual address split. It is not reasonable to have 0xc0553fb4 as page offset. You should c0000000 for 3/1 split.

My fault. I had done "0x%llx" in printk. Now I just did a %x and it shows as 0xc0000000.

-Gautam.