Re: i8042 access timings

[Linus Torvalds]

On Thu, 27 Jan 2005, Jaco Kroon wrote:
>
> Hmm, just an idea, shouldn't the i8042_write_command be waiting until 
> the device has asserted the pin to indicate that the buffer is busy? 

No. Because then you might end up waiting forever for the _opposite_ 
reason, namely that the hardware was so fast that you never saw it busy.

> > The IO delay should be _before_ the read of the status, not after it.
> > 
> > So how about adding an extra "udelay(50)" to either the top of 
> > i8042_wait_write(), or to the bottom of "i8042_write_command()"? Does that 
> > make any difference?
>
> No.  No difference, still the same result.

Oh, well. It was such a good theory, especially as it works fine with ACPI 
off (if I understood your report correctly), so some other state is what 
seems to bring it on.

> > (50 usec is probably overkill, and an alternative is to just make the
> > write_data/write_command inline functions in i8042-io.h use the
> > "inb_p/outb_p" versions that put a serializing IO instruction in between,
> > which should give you a nice 1us delay even on modern hardware.)
>
> ok, how would I try this?  Where can I find an example to code it from? 
>   Sorry, I should probably be grepping ...

If the udelay() didn't work, then this one isn't worth worryign about 
either. Back to the drawing board.

		Linus
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