linux-kernel - Re: PCI resource unavailable on mips

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Date:	Mon, 17 Dec 2007 10:16:31 -0500
From:	Jon Dufresne <jon.dufresne@...initevideocorporation.com>
To:	Ralf Baechle <ralf@...ux-mips.org>
Cc:	linux-kernel@...r.kernel.org, linux-mips@...ux-mips.org
Subject: Re: PCI resource unavailable on mips

I did a bit more work and investigation on this and it turns out I could
not read the mmio in kernel space because I had not done a
pci_enable_device_bars() on the device. I had never done this on x86 so
I didn't realize it was necessary.

> The virtual address 0xc0300000 looks sensible and the physical address
> 0x24000000 is consistent with what you found in the BAR registers.  So that
> all looks reasonable but that only means not obviously wrong.  So next I
> wonder what the value of PCI_MMIO_BASE is ...

The PCI_MMIO_BASE is a defined as:

> #define PCI_MMIO_BASE            (0x00040000)

This is define in the technical documentation as the offset to access
pci config space from the mmio. I am using this because I know what the
values should be so it provides a nice sanity check.

> A bus error is an exception which is signalled by agent external (often
> called system controller) to the CPU core to signal a fatal error during a
> read or write bus transaction, for example after a bus timeout or if the
> address of the read/write isn't assigned to any device.  PCI master abort
> also is often mapped to a bus error exception.

So after doing pci_enable_bars() I can now access this mmio region in
kernel space. However, if I try to mmap this into user space I still
receive the bus error. I am mapping this into user space using the
example for LDD which says to use the remap_pfn_range() function. I've
tested this on the x86 and it works as expected, however every time I
access the mmio from user space using the mips, I continue to get the
bus error I previously received in kernel space.

Any idea what I might be doing wrong? How can I access this from user
space?

Thanks,
Jon

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