Re: Physical memory addresses/PCI memory addresses/io_remap

Re: Physical memory addresses/PCI memory addresses/io_remap

[Petr Vandrovec]

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
                                                    
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/

Re: Physical memory addresses/PCI memory addresses/io_remap

[Alan Cox]

> > 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.

It returns a cookie for use with ioremap. Who says that a given device has
a constant bus or physical mapping that is unique ?

> > 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.

No. Ioremap takes a cookie and returns a different cookie suitable for using
with readb/writeb/memcpy_fromio and friends.

Eg on Sparc64 its a physical address and readb uses TLB bypass

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/