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Re: [Qemu-devel] Linux 2.6.21 doesn't work with qemu-arm SCSI controller

From: andrzej zaborowski
Subject: Re: [Qemu-devel] Linux 2.6.21 doesn't work with qemu-arm SCSI controller anymore.
Date: Tue, 26 Jun 2007 16:41:32 +0200

On 07/06/07, Rob Landley <address@hidden> wrote:
In the 2.6.21 kernel the sym53c8xx_2 SCSI controller changed in a way that
QEMU's virtual SCSI controller doesn't handle this properly:

I spent some time yesterday trying to find out what was happening and
the results are below.

QEMU's virtual SCSI controller does handle it properly and the kernel
sym53c8xx_2 driver changes are not at fault.

The first surprising fact, and one which took me long to figure out,
was that all the SCSI errors are a result of a case of simple
interrupts from the controller not reaching the SCSI driver, hence the
timeouts and whatnot. The sym53c8xx_2 driver gets irq 0 instead of 27,
from the tiwsted PCI irq number assignment logic. This was because the
VersatilePB PCI driver was reading the irq pin number from a wrong
address in the scsi controller's (which is a pci device) config
structure, and the read always returned a 0 which normally means that
the device uses no interrupts (actually all 8-bit accesses were
broken). I corrected the versatile PCI code and sent a patch to linux.
However, the funny part is that this code had not changed since
2.6.18, so how did it break in 2.6.21? Well, it was broken all the
time, but there was a bug in generic PCI code in
drivers/pci/setup-irq.c, which effectively caused the value read from
the device's supplied config, to be discarded, which got fixed in

If you definitely must use 2.6.21, this qemu workaround also works
(need to do the same for any other PCI device you want to use):
diff --git a/hw/lsi53c895a.c b/hw/lsi53c895a.c
index 19bf2a1..eedbc1d 100644
--- a/hw/lsi53c895a.c
+++ b/hw/lsi53c895a.c
@@ -1845,6 +1845,7 @@ void *lsi_scsi_init(PCIBus *bus, int devfn)
    s->pci_dev.config[0x02] = 0x12;
    s->pci_dev.config[0x03] = 0x00;
    s->pci_dev.config[0x0b] = 0x01;
+    s->pci_dev.config[0x3c] = 0x01; /* ugly workaround */
    s->pci_dev.config[0x3d] = 0x01; /* interrupt pin 1 */

    s->mmio_io_addr = cpu_register_io_memory(0, lsi_mmio_readfn,


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