Writing device drivers: How to access a specific memory area?

[Rui Paulo]

On 25 Dec 2008, at 09:53, Andre Albsmeier wrote:

> Hello all,
>
> I am writing a driver which needs to access memory at a
> specific location. The location depends on what the BIOS
> has configured into the host bridge. For example, my
> current machine uses an Intel 975X chipset and the memory
> location I am interested in has been set to 0xFED14000 and
> is 16KB in size (this is MCHBAR of the 975X memory hub).

You probably just need to do something like:

rid = PCI_BAR(number);
res = bus_alloc_resource_any(dev, SYS_RES_MEMORY, &rid, RF_ACTIVE);

And then,
bus_read_4(res, offset from specified PCI BAR);

>
>
> I have no idea how to access this space from my driver.
> I have played around with bus_alloc_resource() but this
> only gives me back NULL.
>
> However, a devinfo -r gives me:
>
> nexus0
>  npx0
>  acpi0
>      Interrupt request lines:
>          9
>      I/O ports:
>          0x10-0x1f
> ...
>          0x800-0x87f
>      I/O memory addresses:
>          0x0-0x9ffff
>          0xc0000-0xdffff
>          0xe0000-0xfffff
>          0x100000-0x7fffffff
>          0xf0000000-0xf3ffffff
>          0xfec00000-0xfec00fff
>          0xfed13000-0xfed19fff		<---
>          0xfed1c000-0xfed1ffff
>          0xfed20000-0xfed3ffff
>          0xfed50000-0xfed8ffff
>          0xfee00000-0xfee00fff
>          0xffb00000-0xffbfffff
>          0xfff00000-0xffffffff
>    cpu0
> ...
>
> The line marked with <--- shows the range which includes
> the location I am interested in. It is probably assigned
> to the acpi0 device.
>
> How do I proceed from this? Do I have to hack around in
> the ACPI-Code? I don't hope so ;-)

You'll probably need to create a fake ACPI child driver to access it.


Create your identify routine with something like:

static void mydriver_identify(driver_t *driver, device_t parent)
{
	if (device_find_child(parent, "mydriver", -1) == NULL &&
	    mydriver_match(parent))
		device_add_child(parent, "mydriver", -1);
}

mydriver_match() should check if you were given the acpi0 device.


>
>
> I only need access to this memory location during the
> probe of my driver to read some configuration data.

Is this pci configuration space ? If so, pci_read_config (man 9 pci)  
should be just what you need.

Regards,
--
Rui Paulo