Accessing 64-bit BARs

Accessing 64-bit BARs

[yogeshwar sonawane]

Hello all,

For accessing memory-mapped 64bit-BAR regions of a PCI card, the
respective BAR regions has to be made accessible to the kernel using
ioremap() function. Then readl()/writel() can be used on the address
returned by ioremap().

I am doing the similar steps to access the BARs of a card.
I observed some change in the behaviour in two different kernels.

Start physical addr of BAR is allocated by BIOS.
In linux-2.6.9, whether BAR start phys addr is below OR above 4GB,
i.e. whether 32-bit BAR phys addr(all higher bits 0) OR 64-bit phys
addr(some higher bits non-zero), I am able to access the BAR region
using ioremap() & then readl()/writel().

For linux-2.6.22-8, if BAR start phys addr is below 4GB, things are
working fine here also.

But, for linux-2.6.22-8, when BAR start phys addr is above 4GB, I am
not able to read/write on the BAR region. ioremap() is not failing.
But read data is all 1's instead of actual data.

Any ideas on where to look for?
Is there any change in the way of accessing 64-bit BAR?
OR
i am missing any step ?

For info - I am using 64-bit OS on x86_64 arch.

-Yogeshwar

Re: Accessing 64-bit BARs

[Rolf Eike Beer]

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Am Donnerstag, 4. Oktober 2007 schrieb yogeshwar sonawane:
> Hello all,
>
> For accessing memory-mapped 64bit-BAR regions of a PCI card, the
> respective BAR regions has to be made accessible to the kernel using
> ioremap() function. Then readl()/writel() can be used on the address
> returned by ioremap().

You should use pci_iomap() to get an access pointer to the BAR. After this you 
can access the memory with ioread*() and iowrite*(). See "man pci_iomap(9)" 
if you build kernel manpages.

Greetings,

Eike

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Re: Accessing 64-bit BARs

[Roland Dreier]

 > You should use pci_iomap() to get an access pointer to the BAR. After this you 
 > can access the memory with ioread*() and iowrite*(). See "man pci_iomap(9)" 
 > if you build kernel manpages.

That works fine, but ioremap() and readl()/writel() is also perfectly
fine for regions that you know are always MMIO.

 - R.

Re: Accessing 64-bit BARs

[yogeshwar sonawane]

hello,
Thanks rolf & roland.

pci_iomap() is not doing something extra. only it is some kind of
abstraction for IO-mapped OR memory mapped.
I know that my BARs are MMIO, so using ioremap() & readl()/writel()
combination should be fine.

But for the problem as explained in my first mail, any
help/suggestions will be helpful.

-Yogeshwar

On 10/4/07, Roland Dreier <rdreier@cisco.com> wrote:
>  > You should use pci_iomap() to get an access pointer to the BAR. After this you
>  > can access the memory with ioread*() and iowrite*(). See "man pci_iomap(9)"
>  > if you build kernel manpages.
>
> That works fine, but ioremap() and readl()/writel() is also perfectly
> fine for regions that you know are always MMIO.
>
>  - R.
>