On virt_to_phys doubts.

[mind entropy]

On Sat, Sep 13, 2014 at 2:01 PM, Miles MH Chen <orca.chen at 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 at 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.
>>
>> _______________________________________________
>> Kernelnewbies mailing list
>> Kernelnewbies at kernelnewbies.org
>> http://lists.kernelnewbies.org/mailman/listinfo/kernelnewbies
>
>

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.