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Re: [PATCH 4/8] hw/ppc/ppc440_bamboo: Drop use of ppcuic_init()

From: Mark Cave-Ayland
Subject: Re: [PATCH 4/8] hw/ppc/ppc440_bamboo: Drop use of ppcuic_init()
Date: Mon, 11 Jan 2021 18:22:46 +0000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:78.0) Gecko/20100101 Thunderbird/78.6.0

On 11/01/2021 17:14, Peter Maydell wrote:

On Sat, Dec 12, 2020 at 12:15:33AM +0000, Peter Maydell wrote:
Switch the bamboo board to directly creating and configuring the UIC,
rather than doing it via the old ppcuic_init() helper function.

Hopefully reporting this here is okay, I find Launchpad hard to use but
I can file it there if need be.

Email reports are fine, thanks.

This patch causes a panic while trying to boot a ppc44x_defconfig Linux

Sorry, yes, this is a bug in this commit of mine. I didn't notice
in the conversion that Bamboo has a non-standard DCR base register
value. I'll just send a patch for this in a second.

Thanks for the repro case.

NB: with the fix for the the kernel proceeds on to the PCI
related assert that it hit in 5.2.

FWIW the assert() seems to be the same problem that Guenter reported at https://lists.gnu.org/archive/html/qemu-devel/2020-12/msg05847.html.

According to Linux's bamboo.dts the PCI slots look this:

    /* Bamboo has all 4 IRQ pins tied together per slot */
    interrupt-map-mask = <0xf800 0x0 0x0 0x0>;
    interrupt-map = <
        /* IDSEL 1 */
        0x800 0x0 0x0 0x0 &UIC0 0x1c 0x8

        /* IDSEL 2 */
        0x1000 0x0 0x0 0x0 &UIC0 0x1b 0x8

        /* IDSEL 3 */
        0x1800 0x0 0x0 0x0 &UIC0 0x1a 0x8

        /* IDSEL 4 */
        0x2000 0x0 0x0 0x0 &UIC0 0x19 0x8

But the assert() is suggesting that we are getting an PCI IRQ of -1 which can only come from slot 0 which isn't physically possible:

/* On Bamboo, all pins from each slot are tied to a single board IRQ. This
 * may need further refactoring for other boards. */
static int ppc4xx_pci_map_irq(PCIDevice *pci_dev, int irq_num)
    int slot = PCI_SLOT(pci_dev->devfn);

    trace_ppc4xx_pci_map_irq(pci_dev->devfn, irq_num, slot);

    return slot - 1;

And indeed the backtrace shows that the PCI host bridge itself is generating 
this IRQ:

(gdb) bt
#0  ppc4xx_pci_map_irq (pci_dev=0x555556c0efe0, irq_num=0) at 
#1 0x00005555559420d9 in pci_change_irq_level (pci_dev=0x555556c0efe0, irq_num=0, change=0) at ../hw/pci/pci.c:266 #2 0x0000555555944d56 in pci_update_irq_disabled (d=0x555556c0efe0, was_irq_disabled=0) at ../hw/pci/pci.c:1386 #3 0x0000555555945086 in pci_default_write_config (d=0x555556c0efe0, addr=4, val_in=1030, l=2) at ../hw/pci/pci.c:1426 #4 0x0000555555aa5b7e in pci_host_config_write_common (pci_dev=0x555556c0efe0, addr=4, limit=256, val=1030, len=2) at ../hw/pci/pci_host.c:83 #5 0x0000555555aa5ce2 in pci_data_write (s=0x555556c0e400, addr=2147483652, val=1030, len=2) at ../hw/pci/pci_host.c:120 #6 0x0000555555aa5e08 in pci_host_data_write (opaque=0x555556c0ce70, addr=0, val=1030, len=2) at ../hw/pci/pci_host.c:167 #7 0x0000555555cb4797 in memory_region_write_accessor (mr=0x555556c0d280, addr=0, value=0x7fffe60234a8, size=2, shift=0, mask=65535, attrs=...)
    at ../softmmu/memory.c:491

The assert() is correct since it correctly identifies an underflow of the PCI IRQ array but what is the best solution? I guess the possibilities are to either i) map the PCI host bridge IRQ to PCI IRQ 0 so at least it doesn't fail or ii) add an extra PCI IRQ 0 for the PCI host bridge and leave it unconnected.



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