Re: map iomem in linux_2_4_dev

[David Gibson <david@gibson.dropbear.id.au>]

On Wed, May 29, 2002 at 01:57:34PM +0900, Sangmoon Kim wrote:
>
> Hi,
> >
> > You don't need io_block_mapping.  Follow one of the many examples to
> > use early_serial_init with an ioremap call for your UART.
> >
> > The only reason your method works is that the io_block_mapping is
> > actually using a BAT on our classic PPC platform.  ioremap will
> > look for an existent BAT mapping and just return the translated
> > virtual address in this case.  Relying on this is bad practice
> > since it will not work on other PPC systems.
> >
> Right, I exactly wanted to do that.
> I called io_block_mapping() on initialization code.
> More precisly on <board name>_map_io(),
> which is in arch/ppc/platforms/<board_name>_setup().
> It has nothing to do with competibility.
> And... Is there any ppc without BAT?
> I didn't know that.

Yes there are PPCs without BATs.  e.g. 4xx.

> > As David correctly pointed out, only use io_block_mapping when
> > you absolutely must control the placement of the virtual address.
> Than, if the system initialization code is changed,
> the driver code should be changed too.

That's exactly why ioremap() is preferred - then the initialization
code doesn't need to touch it at all.

> > There are cases when this is necessary since the hardware engineers
> > always send us garbage to support.  Mapping a UART at init time is
> > not one of these.
> >
> Actually, I'm a hardware guy.
> In most cases, mapping UART is not needed,
> but on the hardware I designed, it is needed.
> Because its physical addres is 0x78000000.
> Don't blame us too much.
> It takes much money to change hardware.

Rubbish.  Having a *physical* address of 0x78000000 is no problem at
all, ioremap() will map that (like any other physical address) into a
sensible virtual address.

--
David Gibson			| For every complex problem there is a
david@gibson.dropbear.id.au	| solution which is simple, neat and
				| wrong.  -- H.L. Mencken
http://www.ozlabs.org/people/dgibson

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