Re: [Qemu-devel] qemu-system-ppc -m g3beige -hda is setting /dev/hdc on Linux.

[Aurelien Jarno <aurelien@aurel32.net>]

On Sat, Feb 13, 2010 at 11:28:44AM +0100, Alexander Graf wrote:
> 
> On 13.02.2010, at 09:02, Rob Landley wrote:
> 
> > The -hda, -hdb, -hdc, and -hdd command line options for g3beige don't match 
> > the order the kernel assigns the drives.
> > 
> > The reason is that the  Linux kernel always initializes the cmd646 driver 
> > before the pmac driver, thus if there's a cmd646 it gets /dev/hda and 
> > /dev/hdb, and the pmac gets /dev/hdc and /dev/hdb.
> > 
> > If you only supply an -hda (and/or -hdb) with no -hdc or -hdd, then the cmd646 
> > driver never attaches to anything and only the pmac controller shows up, thus 
> > -hda and -hdb set /dev/hda and /dev/hdb.  But if you specify a -hdc it shows 
> > up as /dev/hda every time, and kicks the -hda entry to /dev/hdc.
> > 
> > Note that neither the kernel's CONFIG_BLK_DEV_IDE_PMAC_ATA100FIRST nor 
> > CONFIG_IDEPCI_PCIBUS_ORDER made any difference, because those affect multiple 
> > devices handled by the same driver, and this is a static driver initialization 
> > order issue.  When you statically link in both drivers, cmd64x always probes 
> > before pmac due to the above hardwired device order in the kernel, 100% 
> > reliable and deterministic.  It's hardwired, and you have to patch the kernel 
> > to change it. 
> > 
> > Here's a patch to the Linux kernel that changes the device probe order so the 
> > kernel behaves like g3beige is expecting it to:
> > 
> > --- a/drivers/ide/Makefile
> > +++ b/drivers/ide/Makefile
> > @@ -39,6 +39,7 @@
> > obj-$(CONFIG_BLK_DEV_AMD74XX)          += amd74xx.o
> > obj-$(CONFIG_BLK_DEV_ATIIXP)           += atiixp.o
> > obj-$(CONFIG_BLK_DEV_CELLEB)           += scc_pata.o
> > +obj-$(CONFIG_BLK_DEV_IDE_PMAC)         += pmac.o
> > obj-$(CONFIG_BLK_DEV_CMD64X)           += cmd64x.o
> > obj-$(CONFIG_BLK_DEV_CS5520)           += cs5520.o
> > obj-$(CONFIG_BLK_DEV_CS5530)           += cs5530.o
> > @@ -76,8 +77,6 @@
> > 
> > obj-$(CONFIG_BLK_DEV_CMD640)           += cmd640.o
> > 
> > -obj-$(CONFIG_BLK_DEV_IDE_PMAC)         += pmac.o
> > -
> > obj-$(CONFIG_IDE_H8300)                        += ide-h8300.o
> > 
> > obj-$(CONFIG_IDE_GENERIC)              += ide-generic.o
> > 
> > 
> > The problem is, the kernel guys will never take that patch upstream because 
> > what they're currently doing isn't actually wrong.  Their behavior is 
> > consistent, the kernel's been probing the same devices in the same order since 
> > the 90's, and they don't really care what order things go in.
> > 
> > The problem is that the association between qemu's command line arguments and 
> > the devices they refer to is somewhat arbitrary.  On the other targets I've 
> > used (arm, mips, x86, and so on), the device QEMU initializes in response to 
> > "-hda" is the one the Linux kernel makes /dev/hda (or /dev/sda), and the one 
> > it intializes in response to "-hdc" is the one Linux makes /dev/hdc.  But in 
> > this case, they don't match up, and that's screwing up my same init/build 
> > script that works fine on all the other tarets.
> > 
> > Here's a patch to QEMU that makes those arguments intialize the devices the 
> > kernel expects them to.  This doesn't change where any of the hardware is on 
> > the board, just which command line arguments associate with which drives:
> 
> This is wrong. On my OpenSUSE 11.1 guest the devices come up in correct order. They also do so on Aurelien's Debian images (IIRC). I guess it mostly works fine when using modules instead of compiled in drivers.
> 
> Please find a real G3 beige and see what's different on it. I'd bet the real difference is that all 4 devices are attached to MacIO. But from what I remember DBDMA with cd-roms wasn't considered stable, hence the use of cmd64x on the second channel.
> 

Exactly, that's the issue to fix here, make DBDMA work with CD-ROM so we
can get rid of the cmd64x controller.

-- 
Aurelien Jarno	                        GPG: 1024D/F1BCDB73
aurelien@aurel32.net                 http://www.aurel32.net