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Re: [Qemu-devel] qemu-system-ppc -m g3beige -hda is setting /dev/hdc on
Re: [Qemu-devel] qemu-system-ppc -m g3beige -hda is setting /dev/hdc on Linux.
Sat, 13 Feb 2010 13:04:03 +0100
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
>>> driver never attaches to anything and only the pmac controller shows up,
>>> -hda and -hdb set /dev/hda and /dev/hdb. But if you specify a -hdc it
>>> 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
>>> devices handled by the same driver, and this is a static driver
>>> order issue. When you statically link in both drivers, cmd64x always
>>> 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
>>> to change it.
>>> Here's a patch to the Linux kernel that changes the device probe order so
>>> 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
>>> 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
>>> 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
>>> "-hda" is the one the Linux kernel makes /dev/hda (or /dev/sda), and the
>>> it intializes in response to "-hdc" is the one Linux makes /dev/hdc. But
>>> 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
>>> 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.