Re: Screen regen buffer at 0x00b8000

["Richard B. Johnson" <linux-os@analogic.com>]

On Fri, 20 May 2005 Valdis.Kletnieks@vt.edu wrote:

> On Fri, 20 May 2005 21:26:59 +0200, Geert Uytterhoeven said:
> > On Fri, 20 May 2005, Richard B. Johnson wrote:
>
> > > I think that I've discovered a bug. I know that what I have written gets
> > > to the screen buffer because I can read in back! This doesn't make
> > > any sense.
> >
> > Even if it's only in the CPU cache, of course you can read it back (using the
> > CPU, not DMA ;-).
>
> No, the bug is in Richard's assuming that because he can read it back in means
> that it's in the screen buffer.  In fact, it only means he wrote it into some
> memory location that he can read back in. ;)
>
> Now if he added a description that verified that a read *from the screen
> buffer*
> (rather than "from where he wrote") shows his changes, *then* he'd have
> something...

Well MAP_FIXED must either mmap the physical location I provided or
it must fail. Since it didn't fail, I figure that it did what I
told it to do. Now, that "FIXED" refers to a fixed offset. Geert is
correct when he says that it's probably just in cache. Now begs
the question... Why would a hardware buffer ever be cached? That's
why I think I found a bug. It certainly shouldn't be cached.

Cheers,
Dick Johnson
Penguin : Linux version 2.6.11.9 on an i686 machine (5554.17 BogoMips).
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