From: ashish anand <ashisha@india.infogain.com>
To: Goddeeris Frederic <Frederic.Goddeeris@siemens.atea.be>,
linuxppc-embedded@lists.linuxppc.org
Subject: Re: "Kernel logical address" vs "Physical"
Date: Fri, 14 Sep 2001 10:20:04 +0530 [thread overview]
Message-ID: <3BA18C7C.F2D4B343@india.infogain.com> (raw)
In-Reply-To: 6B546A602AD2D211BFF00008C7A42889041D6BDE@hrtades2.atea.be
> 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/
next prev parent reply other threads:[~2001-09-14 4:50 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2001-09-14 8:44 "Kernel logical address" vs "Physical" Goddeeris Frederic
2001-09-14 4:50 ` ashish anand [this message]
-- strict thread matches above, loose matches on Subject: below --
2001-09-14 10:52 Goddeeris Frederic
2001-09-14 6:06 ` ashish anand
2001-09-14 11:47 Goddeeris Frederic
2001-09-14 6:49 ` ashish anand
2001-09-14 18:26 ` Dan Malek
2001-09-14 12:13 Goddeeris Frederic
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