Re: "Kernel logical address" vs "Physical"

Re: "Kernel logical address" vs "Physical"

[ashish anand]

> I have been working on a PPC platform, running Linux 2.2. This platform has
> a register where you can enable different options and where you can control
> several LED's. The vendor mentions that this register is mapped in memory at
> FA400000.
>
> When I write (in a driver)
>
> char *p=0xFA40000;
>
> *p = ..; (I know I should use writeb to be more portable.)
>
> it seems to work; the leds can be manipulated. But as FA400000 is a physical
> address, I thought that it had to be *p=__va(0xFA40000);
>
> Who can help me out? Where do I find a nice document about this?

actually when you refer to adress mentioned 0xFA400000 in driver this address is already virtual adress hence no need to  use __va macro.
this address was originally a physical adress and unaccessible from device untill earlier in code
a call for ioremap would have taken place.
after ioremapping it is a virtual address and can be used nicely in a driver.
transaction for this address would be valid as processor has now a entry for it and would be decoded by host bridge and forwarded to LED.
without ioremapping if you use you will get a kernel panic.

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

Re: "Kernel logical address" vs "Physical"

[ashish anand]

> Thank you for your reply! I am afraid that I am still confused...
>
> You say "actually when you refer to address mentioned 0xFA400000 in driver
> this address is already virtual address". The address 0xFA40000 is an
> address that I found in the documentation of the hardware vendor (Embedded
> Planet, the board is an CLLF_BW32), where there is no reference to any OS.
> The table containing the chip select mappings mentions that the "Control and
> Status register" is mapped at FA40. So I assume that 0xfA400000 is a pure
> physical address. Or is this a false assumption?
>
> When I write "char *p=0xFA40000;" it works.
> When I write "char *p=0xFA40000; p = ioremap(p,1);" I get another pointer
> and it works as well... I suppose this could not work when 0xFA40000 was not
> a physical address. When I use p=__va(p); or p=pa(p); it crashes


documentation is alright.
your documentation says that address 0xF4A00000 is a PHYSICAL address mapped for
 LED.but you will not be able to use this adress from processor without ioremapping.
in mmu of processor thee should be entry for virtual ----> physical addreses.

initially this is not , after using ioremap it is created there.

in your case you are getting virtual address = physical addres , probably because of
ioremap_base in the implementation of ioremap.
your physical address is above ioremap_base.
hence physical = virtual.

now path of your transaction from processor -> host bridge -> LED is clear.
this is all about your confusion.
I don't have any idea about your specific board.

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

Re: "Kernel logical address" vs "Physical"

[ashish anand]

Goddeeris Frederic wrote:
>
> So the key is that by address is above ioremap_base. That I initially got
> away with not using ioremap is a coincidence? Right?
>
> Where could I find a complete discussion of how all this is organized? The
> documents I find are or very vague, or explain a small issue and suppose you
> have already solid knowledge about it.

ioremap_base is not unique for every board.
but 0xfaxxxxxx is above ioremap_base for most of situations.
you have to go for high level browsing of memory initialisation codes
in your source tree and do web surfing.
i don't have any idea if it is orgainsed comprehensively in one place.
you serach in your source tree where the address range containing 0xf4axxxxxxhas been
ioremapped.

on some plateform like SPARC there is "vitual io" there you might not need to ioremap
sort of interface for the address range in that "virtual io window" as there is a entry built already for  virtual --> physical ...anybody should correct me if i am wrong here..

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"Kernel logical address" vs "Physical"

[Goddeeris Frederic]

Hi,

I have a fairly basic question about "Kernel logical address" and "Physical
address".


In the book about Linux Device Drivers (first and second edition) from
Alessandro Rubini I read:

"Logical addresses make up the normal address-space of the kernel. . On most
architectures, logical and their associated physical addresses differ only
by a constant offset." __pa() is used to go from logical address to Physical
address; __va() the other way round.



I have been working on a PPC platform, running Linux 2.2. This platform has
a register where you can enable different options and where you can control
several LED's. The vendor mentions that this register is mapped in memory at
FA400000.

When I write (in a driver)

char *p=0xFA40000;

*p = ..; (I know I should use writeb to be more portable.)

it seems to work; the leds can be manipulated. But as FA400000 is a physical
address, I thought that it had to be *p=__va(0xFA40000);



Who can help me out? Where do I find a nice document about this?



Thanks,

Frederic


** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

RE: "Kernel logical address" vs "Physical"

[Goddeeris Frederic]

Hi,

Thank you for your reply! I am afraid that I am still confused...

You say "actually when you refer to address mentioned 0xFA400000 in driver
this address is already virtual address". The address 0xFA40000 is an
address that I found in the documentation of the hardware vendor (Embedded
Planet, the board is an CLLF_BW32), where there is no reference to any OS.
The table containing the chip select mappings mentions that the "Control and
Status register" is mapped at FA40. So I assume that 0xfA400000 is a pure
physical address. Or is this a false assumption?

When I write "char *p=0xFA40000;" it works.
When I write "char *p=0xFA40000; p = ioremap(p,1);" I get another pointer
and it works as well... I suppose this could not work when 0xFA40000 was not
a physical address. When I use p=__va(p); or p=pa(p); it crashes.

Regards,
Frederic

-----Original Message-----
From: ashish anand [mailto:ashisha@india.infogain.com]
Sent: vrijdag 14 september 2001 6:50
To: Goddeeris Frederic; linuxppc-embedded@lists.linuxppc.org
Subject: Re: "Kernel logical address" vs "Physical"
Importance: High



> I have been working on a PPC platform, running Linux 2.2. This platform
has
> a register where you can enable different options and where you can
control
> several LED's. The vendor mentions that this register is mapped in memory
at
> FA400000.
>
> When I write (in a driver)
>
> char *p=0xFA40000;
>
> *p = ..; (I know I should use writeb to be more portable.)
>
> it seems to work; the leds can be manipulated. But as FA400000 is a
physical
> address, I thought that it had to be *p=__va(0xFA40000);
>
> Who can help me out? Where do I find a nice document about this?

actually when you refer to adress mentioned 0xFA400000 in driver this
address is already virtual adress hence no need to  use __va macro.
this address was originally a physical adress and unaccessible from device
untill earlier in code
a call for ioremap would have taken place.
after ioremapping it is a virtual address and can be used nicely in a
driver.
transaction for this address would be valid as processor has now a entry for
it and would be decoded by host bridge and forwarded to LED.
without ioremapping if you use you will get a kernel panic.

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

RE: "Kernel logical address" vs "Physical"

[Goddeeris Frederic]

So the key is that by address is above ioremap_base. That I initially got
away with not using ioremap is a coincidence? Right?

Where could I find a complete discussion of how all this is organized? The
documents I find are or very vague, or explain a small issue and suppose you
have already solid knowledge about it.

Thanks,
Frederic

-----Original Message-----
From: ashish anand [mailto:ashisha@india.infogain.com]
Sent: vrijdag 14 september 2001 8:07
To: Goddeeris Frederic; linuxppc-embedded@lists.linuxppc.org
Subject: Re: "Kernel logical address" vs "Physical"
Importance: High



> Thank you for your reply! I am afraid that I am still confused...
>
> You say "actually when you refer to address mentioned 0xFA400000 in driver
> this address is already virtual address". The address 0xFA40000 is an
> address that I found in the documentation of the hardware vendor (Embedded
> Planet, the board is an CLLF_BW32), where there is no reference to any OS.
> The table containing the chip select mappings mentions that the "Control
and
> Status register" is mapped at FA40. So I assume that 0xfA400000 is a pure
> physical address. Or is this a false assumption?
>
> When I write "char *p=0xFA40000;" it works.
> When I write "char *p=0xFA40000; p = ioremap(p,1);" I get another pointer
> and it works as well... I suppose this could not work when 0xFA40000 was
not
> a physical address. When I use p=__va(p); or p=pa(p); it crashes


documentation is alright.
your documentation says that address 0xF4A00000 is a PHYSICAL address mapped
for
 LED.but you will not be able to use this adress from processor without
ioremapping.
in mmu of processor thee should be entry for virtual ----> physical
addreses.

initially this is not , after using ioremap it is created there.

in your case you are getting virtual address = physical addres , probably
because of
ioremap_base in the implementation of ioremap.
your physical address is above ioremap_base.
hence physical = virtual.

now path of your transaction from processor -> host bridge -> LED is clear.
this is all about your confusion.
I don't have any idea about your specific board.

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

RE: "Kernel logical address" vs "Physical"

[Goddeeris Frederic]

Thanks!

-----Original Message-----
From: ashish anand [mailto:ashisha@india.infogain.com]
Sent: vrijdag 14 september 2001 8:50
To: Goddeeris Frederic; linuxppc-embedded@lists.linuxppc.org
Subject: Re: "Kernel logical address" vs "Physical"


Goddeeris Frederic wrote:
>
> So the key is that by address is above ioremap_base. That I initially got
> away with not using ioremap is a coincidence? Right?
>
> Where could I find a complete discussion of how all this is organized? The
> documents I find are or very vague, or explain a small issue and suppose
you
> have already solid knowledge about it.

ioremap_base is not unique for every board.
but 0xfaxxxxxx is above ioremap_base for most of situations.
you have to go for high level browsing of memory initialisation codes
in your source tree and do web surfing.
i don't have any idea if it is orgainsed comprehensively in one place.
you serach in your source tree where the address range containing
0xf4axxxxxxhas been
ioremapped.

on some plateform like SPARC there is "vitual io" there you might not need
to ioremap
sort of interface for the address range in that "virtual io window" as there
is a entry built already for  virtual --> physical ...anybody should correct
me if i am wrong here..

** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/

Re: "Kernel logical address" vs "Physical"

[Dan Malek]

Goddeeris Frederic wrote:
>
> So the key is that by address is above ioremap_base. That I initially got
> away with not using ioremap is a coincidence? Right?

No, it's not a coincidence.  I've written sufficiently about virtual
space mapping on the embedded processors in the past and if you just
search the mailing list archives you will find all of the answers.

The short answer.....on some processors, like the 8xx, there is a
common address space used by many device drivers and functions
unique to this processor.  The granularity of mapping required is
very small, resulting in many overlapped maps if you constantly use
ioremap() in all of these cases.  For this processor, a common area
is ioremap()'ed by the memory management early in the kernel initialization
for all of these uses.  The side effect of mapping this early is you
get a 1:1 virtual to physical mapping because the kernel VM is not
yet fully initialized.


	-- Dan

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