On 13.02.2010, at 12:58, Aurelien Jarno wrote: > 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.
Speaking of which - in my PPC64 enabling series I use MacIO for all 4 IDE devices. At least with recent kernels, Linux just detects DMA being broken on the CD-ROM and doesn't use it. Alex
