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

[Andre Albsmeier]

On Thu, 25-Dec-2008 at 13:57:00 +0000, Rui Paulo wrote:
> 
> 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);

The problem was, that this memory belongs to acpi0
so I couldn't read it from my driver which has no
resources assigned to it. But, I found a way, see below...

> 
> 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.

Found something easier: I just do a bus_set_resource() followed
by bus_alloc_resource_any(), access my host bridge registers,
and free things with bus_release_resource() followed by
bus_delete_resource().

> 
> 
> >
> >
> > 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)  

Unfortunately not. As I wrote, it is a 16k memory window
where the 975x maps a part of its config registers. The
address of this window can be read by pci_read_config( dev, 0x44, 4 ).
Then you can access the bridge's cXdrcY registers through
this memory window which I needed to determine the
machines RAM layout.

Thanks anyway for your help,

	-Andre