AGPGART driver for ArticiaS - ioremap() problem

Gerhard Pircher gerhard_pircher at
Mon Jan 16 10:10:15 EST 2006

> --- Ursprüngliche Nachricht ---
> Von: Benjamin Herrenschmidt <benh at>
> An: Gerhard Pircher <gerhard_pircher at>
> Kopie: linuxppc-dev at, debian-powerpc at
> Betreff: Re: AGPGART driver for ArticiaS - ioremap() problem
> Datum: Mon, 16 Jan 2006 08:48:28 +1100
> I don't understand. I would need to now more about what
> the bridge actually does to get any sense out of that.

Thanks for answering! It's hard to explain for me what the code does, but I
will try.

I included a cleaned-up version of the AGPGART driver code for the ArticiaS
(AmigaOne/Pegasos1). As mentioned, the driver is based on the VIA AGPGART
driver and uses the agp_generic_create_gatt_table() and
agp_generic_free_gatt_table() functions (well, I copied and renamed this
functions to insert debug code).

Actually at least the bridge does everthing right until now (IMHO :-). The
bridge is detected and also the aperture size is read out correctly from the
registers. After that, the agp_backend_initialize() function in
drivers/cahr/agp/backend.c calls the create_gatt_table() function of the
driver (articias_create_gatt_table). Based on the detected aperture size and
its definitions, this function allocates pages for the GATT table
(alloc_gatt_pages). The function then tries to map this pages with
ioremap_nocache(virt_to_gatt(table, (PAGE_SIZE * (1 << page_order))). But
ioremap_nocache() cannot remap the pages, because the following code snipped
in __ioremap (arch/ppc/mm/pgtable.c) is trigged:

 * Don't allow anybody to remap normal RAM that we're using.
 * mem_init() sets high_memory so only do the check after that.
if ( mem_init_done && (p < virt_to_phys(high_memory)) )
	printk("__ioremap(): phys addr "PHYS_FMT" is RAM lr %p\n", p,
	return NULL;

As it can be seen in the following log, the table address (0xde200000 ->
virt_to_gart(table) = 0x1e200000) is lower than the maximum amount of memory
0x20000000 (512MB) and therefore __ioremap() does not remap the pages.


agpgart: [ARTICIAS] articias_fetch_size()
agpgart: [ARTICIAS] * non masked temp = 0x6
agpgart: [ARTICIAS] * aperature size loop index #0
agpgart: [ARTICIAS] * values[0].size_value = 1
agpgart: [ARTICIAS] * aperature size loop index #1
agpgart: [ARTICIAS] * values[1].size_value = 2
agpgart: [ARTICIAS] * aperature size loop index #2
agpgart: [ARTICIAS] * values[2].size_value = 3
agpgart: [ARTICIAS] * aperature size loop index #3
agpgart: [ARTICIAS] * values[3].size_value = 4
agpgart: [ARTICIAS] * aperature size loop index #4
agpgart: [ARTICIAS] * values[4].size_value = 5
agpgart: [ARTICIAS] * aperature size loop index #5
agpgart: [ARTICIAS] * values[5].size_value = 6
agpgart: [ARTICIAS] * masked temp = 0x6
agpgart: [ARTICIAS] * values[5].size = 128  (128MB aperture size)
agpgart: [ARTICIAS] * current_size->size = 128
agpgart: [ARTICIAS] * current_size->page_order = 5
agpgart: [ARTICIAS] * current_size->num_entries = 32768
agpgart: [ARTICIAS] * current_size->size_value = 6
agpgart: [ARTICIAS] articias_create_gatt_table()
agpgart: [ARTICIAS] * table address = 0xde200000
agpgart: [ARTICIAS] * table end address = 0xde21ffff
agpgart: [ARTICIAS] * page = 0xc09c4400
agpgart: [ARTICIAS] * gatt_table_real = 0xde200000
agpgart: [ARTICIAS] * agp_gatt_table = 0xde200000
agpgart: [ARTICIAS] * virt_to_gart(table) = 0x1e200000
__ioremap() debug: addr = 0x1e200000
__ioremap() debug: phys addr = 0x1e200000
__ioremap() debug: size = 0x20000
__ioremap() debug: Highmem check
__ioremap() debug: high_memory = 0xe0000000
__ioremap() debug: virt_to_phys(high_memory) = 0x20000000
__ioremap(): phys addr 1e200000 is RAM lr c000f210
agpgart: [ARTICIAS] * gatt_table_real = 0x0
agpgart: unable to get memory for graphics translation table.
agpgart: agp_backend_initialize() failed.
agpgart-articias: probe of 0000:00:00.0 failed with error -12

How can I achieve it that ioremap_nocache() can map the pages or that
alloc_gatt_pages() returns valid pages for the GATT table?

Thanks again!



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