ia64 linux question

ia64 linux question

[ratheesh kannoth]

Hi,

I am running  2.6.29.1 on ia-64 hardware.


when i run  below code in a module

void *ptr =  kmalloc( 10 ,GFP_KERNEL )

i got a valid ptr ( ptr != NULL ) ..but i saw that

ptr == vitr_to_phy(ptr ) == virt_to_bus(ptr )

1. why   the physical and vitrual address  are same ?
2. is this sthing that we can change in kernel config during kernel
compilation ?

-Ratheesh
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Re: ia64 linux question

[Anatoliy Sivov]

Hello Ratheesh,

I have no kernel 2.6.29.1 and any ia-64 harware, but looked on modern  
(3.6) kernel sources.
 From arch/ia64/include/asm/io.h you can see that virt_to_phys and  
virt_to_bus are actually the same function.
It's implementation is to return (unsigned long) address - PAGE_OFFSET.
I guess, PAGE_OFFSET for ia-64 is defined in arch/ia64/include/asm/page.h  
as RGN_BASE(RGN_KERNEL).
RGN_KERNEL is a simple constant (equals 7), which obviously determines  
region. Region number (here, 7) is located in top three bits of 64 bit  
address, so RGN_BASE simply shifts its argument with 61 bit (see RGN_SHIFT  
define).
So, writing in numbers: vitr_to_phys (and virt_to_bus) simply returns  
(unsigned long) address - 0xE000000000000000.
The only way you can get ptr == virt_to_phys(ptr) is incorrectly treating  
operands as 32-bit numbers (i.e. printk("%u", ptr) instead of  
printk("%lu", ptr)).

BR, Anatoliy Sivov

ratheesh kannoth <ratheesh.ksz@gmail.com> писал(а) в своём письме Wed, 14  
Nov 2012 14:11:14 +0400:

> Hi,
>
> I am running  2.6.29.1 on ia-64 hardware.
>
>
> when i run  below code in a module
>
> void *ptr =  kmalloc( 10 ,GFP_KERNEL )
>
> i got a valid ptr ( ptr != NULL ) ..but i saw that
>
> ptr == vitr_to_phy(ptr ) == virt_to_bus(ptr )
>
> 1. why   the physical and vitrual address  are same ?
> 2. is this sthing that we can change in kernel config during kernel
> compilation ?
>
> -Ratheesh
> --
> To unsubscribe from this list: send the line "unsubscribe linux-newbie"  
> in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
> Please read the FAQ at http://www.linux-learn.org/faqs

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