From: David Gibson <david@gibson.dropbear.id.au>
To: linuxppc-embedded@lists.linuxppc.org
Subject: Re: map iomem in linux_2_4_dev
Date: Wed, 29 May 2002 15:47:37 +1000 [thread overview]
Message-ID: <20020529054737.GE16537@zax> (raw)
In-Reply-To: <002b01c206cd$59f7a760$1a11efcb@industrialDiv.hanasys.co.kr>
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
** Sent via the linuxppc-embedded mail list. See http://lists.linuxppc.org/
next prev parent reply other threads:[~2002-05-29 5:47 UTC|newest]
Thread overview: 15+ messages / expand[flat|nested] mbox.gz Atom feed top
2002-05-28 10:38 map iomem in linux_2_4_dev Sangmoon Kim
2002-05-28 13:23 ` Matt Porter
2002-05-29 4:57 ` Sangmoon Kim
2002-05-29 5:47 ` Roland Dreier
2002-05-29 6:01 ` Sangmoon Kim
2002-05-29 5:47 ` David Gibson [this message]
2002-05-29 6:14 ` Sangmoon Kim
2002-05-29 12:48 ` shaowei dai
-- strict thread matches above, loose matches on Subject: below --
2002-05-27 5:59 shaowei dai
2002-05-27 6:34 ` David Gibson
2002-05-27 6:51 ` shaowei dai
2002-05-27 8:13 ` Sangmoon Kim
2002-05-27 8:13 ` shaowei dai
2002-05-28 0:36 ` David Gibson
2002-05-28 4:42 ` Sangmoon Kim
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