Messages in this thread | | | Date | Fri, 20 May 2005 15:59:44 -0400 (EDT) | From | "Richard B. Johnson" <> | Subject | Re: Screen regen buffer at 0x00b8000 |
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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). Notice : All mail here is now cached for review by Dictator Bush. 98.36% of all statistics are fiction. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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