Messages in this thread | | | From | Benjamin Herrenschmidt <> | Subject | Re: IO issues vs. multiple busses | Date | Sun, 4 Mar 2001 20:55:33 +0100 |
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>So once again I vote for the introduction of >isa_{request,release}_mem_region(), just like we already have isa_readb() and >friends.
Well, it's the same problem as the IO, there may be more than one ISA mem region, especially when you put 2 video cards on 2 different PCI hosts (even without a PCI-ISA bridge).
In fact, with a PCI-ISA bridge, I can imagine a config where you need 2 ISA IO regions and 2 ISA mem regions on the same PCI bus if that bridge does address translation.
My concern for now is mostly to get video cards fixed, I don't care much about legacy ISA hardware as in those case, I guess we can limit ourselves to a single ISA bus and inb/oub beeing happy to cope with it.
The problem is that we use the same macros (inb/outb) to access that ISA bus, and to access any PCI IO bus. Well, I would suggest the following:
- inb/outb without offset -> the ISA bus if any, or the IO space of the first PCI host - inb/outb with offset (or encoded HBA number) -> IO space of an other bus - pci_get_bus_io_base() returns the IO offset for accessing the Nth PCI bus IO space so that the fb devs can do VGA IOs on the bus that holds their card. - pci_get_bus_isa_mem_base() returns the base address at which isa mem is available for a given PCI bus (that is the address that generates mem cycles in the range 0->64k). This is a physical address, the driver still have to ioremap it. Some PCI cards can have a BAR mapping the VGA memory elsewhere, drivers for those cards should prefer the BAR mapping of course.
All IO ranges can be mapped via kernel VM tricks into a single contiguous space with the offset beeing something like a 64k increment, or we can have the inb/outb do a lookup of the host bus like on parisc. That's an arch implementation detail.
Is that ok ? I know it's not perfect, but it would allow to solve the most important problem for now. The PCI cards in need of IOs (like PCI IDE cards) can have their resources fixed up by the arch code in order to tap the correct bus. Only the real legacy ISA drivers will be limited to the fixed (default) ISA bus.
Ben.
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