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SubjectRe: RFC: Devices, buses and hotplug
Hello,

> Allocating the entire device strikes me as extremely limiting.

I didn't say it's the only possibility :-)) Anyway, it's fine for
most cases.

> parport already needs to share the same parallel port,

Think of parport as of a bus with virtual devices corresponding to
the devices daisy-chained on the parport.

> and the stuff I
> am interested in -- VGA and video drivers -- often wind up needing to
> share the VGA ports. In order to support multiple VGA cards in a single
> machine, I do this
>
> pci_disable_other_vga_card_io_regions()
> pci_enable_my_vga_card_io_regions()
>
> { the fb driver does some VGA port I/O }
>
> pci_disable_my_vga_card_io_regions()
> pci_enable_other_vga_card_io_regions()

VGA ports certainly cannot be handled as ordinary PCI I/O ports since they
don't obey any sane rules. Support of multiple VGA cards is a nightmare
and basically it's going to contain a lot of card-dependent code and be
handled by an extra kernel module. No need to encumber the generic resource
management stuff with this.

> This is definitely important, as one particular S3 card will report its
> MMIO region as 32 MB instead of the correct 64 MB.

Yes, this is exactly the case where we need to relocate a PCI card
even in a non-hotplug environment. Anyway, except for such cases we should
avoid PCI relocation as otherwise we'd have to know about all non-standard
host bridges.

> Slightly off topic: What about AGP? Is any work or planning going on
> in that direction? I know it's compatible with PCI, but there don't
> seem to be any constants in the kernel yet for accessing the new
> configuration commands and such.

From the configuration point of view, AGP is identical to PCI. Maybe
generic AGP access routines will appear one day, but for now I know of
no driver needing it.

Have a nice fortnight
--
Martin `MJ' Mares <mj@ucw.cz> http://atrey.karlin.mff.cuni.cz/~mj/
Faculty of Math and Physics, Charles University, Prague, Czech Rep., Earth
"MIPS: Meaningless Indicator of Processor Speed."

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