On 7/13/07, Gregory Haskins <[EMAIL PROTECTED]> wrote: > On Fri, 2007-07-13 at 16:46 +0200, Luca wrote: > > On 7/13/07, Gregory Haskins <[EMAIL PROTECTED]> wrote: > > > Just to clarify: you are suggesting that the "old" IDE driver used to > > see that the controller was disabled and reprogrammed it by itself > > (fast mode); now it sees it's enabled and leaves whatever mode is > > currently set. > > I can't look at the sources right now but it's at least plausible ;-) > > > > Yeah. As Im sure you are aware, those bits that your patch modifies are > (IIUC) for enabling/disabling access to the legacy IDE. On real > hardware, they can be used by the bios to enable/disable the legacy IDE > function. It doesnt actually disable the chip IIUC..
Hum, are you *really* sure? Intel doc says: "IDE Decode Enable (IDE). 1=Enable; 0=Disable. When enabled, I/O transactions on PCI targeting the IDE ATA register blocks (command block and control block) are positively decoded on PCI and driven on the IDE interface. When disabled, these accesses are subtractively decoded to ISA." Now, "subtractively decoded to ISA" means that if nobody wants them then those accesses are left to ISA devices (the PCI-to-ISA bridge forwards them). So IIRC setting the decode enable to 0 really means "disable the controller". > its just a flag to let higher layer software detect if the legacy IDE is > usable. In our > emulated environment, those bits were left undefined prior to your patch > (neither qemu nor bochs was configuring them). Bochs *is* enabling the ports; it's just that it does that in the emulated device (i.e. the equivalent of out hw/ide.c) and not in the BIOS. Btw, the original thread is there: http://thread.gmane.org/gmane.comp.emulators.kvm.devel/3619 > So what I am thinking is that the drivers included with the FC7 kernel > are defaulting to some kind of slower legacy mode when they see it is > available and enabled. Otherwise, they probably load some direct > non-legacy PCI driver and use that instead. Nope, FC7 with libata doesn't find anything at all. It doesn't even try to touch the controller if the ports are not enabled. This makes a lot of sense since with ports disabled all the access to the command and control blocks are forwarded to the ISA worlds (since the IDE controller is not claiming the transactions). I guess that the old driver has some logic like "BIOS is stupid, we really want to enable this port". Still, I fail to see why enabling the ports should reduce the speed. Dave, can you confirm that backing out my patch fixes your speed issue? Luca ------------------------------------------------------------------------- This SF.net email is sponsored by DB2 Express Download DB2 Express C - the FREE version of DB2 express and take control of your XML. No limits. Just data. Click to get it now. http://sourceforge.net/powerbar/db2/ _______________________________________________ kvm-devel mailing list kvm-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/kvm-devel
