Messages in this thread |  | | From | Russell King <> | Subject | Re: VGA PCI IO port reservations | Date | Fri, 17 Nov 2000 16:56:47 +0000 (GMT) |
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Brian Gerst writes: > This is an artifact from the ISA 10-bit IO bus. Many ISA cards do not > decode all 16 address bits so you get aliases of the 0x100-0x3ff region > throughout IO space. PCI cards should only use the first 256 ports of > any 1k block to avoid aliases unless they claim the base alias. For > example, all the xxe8 addresses for the S3 are aliases of 0x02e8 to an > ISA card. Video cards are an exception to the general rule because they > have to support all the legacy VGA crap.
No. All xxe8 addresses access specific registers. For example:
0x9ea8 is the drawing command 0xa2e8 is the background colour register 0xa6e8 is the foreground colour register
So, as you see they aren't aliases.
> /* > * We need to avoid collisions with `mirrored' VGA ports > * and other strange ISA hardware, so we always want the > * addresses to be allocated in the 0x000-0x0ff region > * modulo 0x400. > * > * Why? Because some silly external IO cards only decode > * the low 10 bits of the IO address. The 0x00-0xff region > * is reserved for motherboard devices that decode all 16 > * bits, so it's ok to allocate at, say, 0x2800-0x28ff, > * but we want to try to avoid allocating at 0x2900-0x2bff > * which might have be mirrored at 0x0100-0x03ff.. > */
Ah ha, I'll nick that for the ARM stuff then. Thanks for pointing it out. _____ |_____| ------------------------------------------------- ---+---+- | | Russell King rmk@arm.linux.org.uk --- --- | | | | http://www.arm.linux.org.uk/personal/aboutme.html / / | | +-+-+ --- -+- / | THE developer of ARM Linux |+| /|\ / | | | --- | +-+-+ ------------------------------------------------- /\\\ | - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org Please read the FAQ at http://www.tux.org/lkml/
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