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Re: [Qemu-devel] qemu-system-ppc -m g3beige -hda is setting /dev/hdc on
From: |
Aurelien Jarno |
Subject: |
Re: [Qemu-devel] qemu-system-ppc -m g3beige -hda is setting /dev/hdc on Linux. |
Date: |
Sat, 13 Feb 2010 13:32:58 +0100 |
User-agent: |
Mutt/1.5.18 (2008-05-17) |
On Sat, Feb 13, 2010 at 01:04:03PM +0100, Alexander Graf wrote:
>
> 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.
>
Same on PPC32, except that when DMA is not used, the VM freeze after a
few accesses to the drive.
--
Aurelien Jarno GPG: 1024D/F1BCDB73
address@hidden http://www.aurel32.net