From: "Petr Vandrovec" <VANDROVE@vc.cvut.cz>
Organization: CC CTU Prague
To: Russell King <rmk@arm.linux.org.uk>
Date: Thu, 14 Dec 2000 17:56:54 MET-1
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Subject: Re: Physical memory addresses/PCI memory addresses/io_remap
CC: linux-kernel@vger.kernel.org
Message-ID: <FA894952830@vcnet.vc.cvut.cz>
Sender: linux-kernel-owner@vger.kernel.org

On 14 Dec 00 at 15:16, Russell King wrote:
>   virtual space    - address space that the kernel runs in
>   physical space   - address space that the CPU sits in
>   PCI memory space - memory address space that the PCI peripherals sit in
    == bus address...
> 
> Many, if not all ARM architectures have physical address 0 different from
> PCI memory address 0.
> 
> According to include/linux/fb.h, fb drivers should place a physical address
> into "fix.smem_start" and "fix.mmio_start", which can then be passed to
> io_remap_page_range.
> 
> 1. Should pci_resource_start be returning the PCI memory space address or
>    a physical memory space address?

I believe that pci_resource_start() should return physical address, not
bus one. It already happens on PReP.
 
> 3. Do we need a macro to convert PCI memory space addresses to physical
>    memory space addresses?

No. You need PCI memory space address only for busmastering transfers.
And for PCI DMA there is specialized API... Currently all bus -> physical
mapping should be hidden in platform specific PCI code.
 
> 4. What does this mean for ioremap?  (currently, on ARM, ioremap takes
>    PCI memory space addresses, not a physical memory address, which makes
>    the physmap MTD driver technically broken).

And ioremap() should take physical address, returning virtual one.
                                            Best regards,
                                                    Petr Vandrovec
                                                    vandrove@vc.cvut.cz
                                                    
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