Cc: Ondrej Zary <linux@...>, H. Peter Anvin <hpa@...>, Rene Herman <rene.herman@...>, Bodo Eggert <7eggert@...>, Ingo Molnar <mingo@...>, Alan Cox <alan@...>, Paul Rolland <rol@...>, Pavel Machek <pavel@...>, Thomas Gleixner <tglx@...>, <linux-kernel@...>, Ingo Molnar <mingo@...>, <rol@...>
On Tue, 08 Jan 2008 13:44:54 -0500
"David P. Reed" <dpreed@reed.com> wrote:
Now you're totally confusing things. You're talking about looking at
bits in a register to see if a transmit register is empty.
That's easy.
The delays needed for the Intel M8259 and M8253 say that you're not
even allowed to access the registers _at_ _all_ for some time after a
register access. If you do a write to a register immediately followed
by any access, including a read of the status register, you can corrupt
the state of the chip.
And the Intel chips are not the only ones with that kind of brain
damage. But what makes the 8259 and 8253 a big problem is that every
modern PC has a descendant of those chips in them. The discrete Intel
chips or clones got aggregated into Super I/O chips, and the Super I/O
chips were put on a LPC bus (an ISA bus with another name) or
integrated into the southbrige. And the "if it ain't broken, don't fix
it" mantra probably means that some modern chipsets are still using
exactly the same internal design as the 25 year old chips and will
still be subject to some of those ancient limitations.
/Christer
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