Re: [PATCH 09/13] hw/ide/piix: Disuse isa_get_irq()

[Bernhard Beschow]

Am 27. April 2023 12:31:10 UTC schrieb Mark Cave-Ayland 
<mark.cave-ayland@ilande.co.uk>:
>On 26/04/2023 19:25, Bernhard Beschow wrote:
>
>> Am 26. April 2023 11:33:40 UTC schrieb Mark Cave-Ayland 
>> <mark.cave-ayland@ilande.co.uk>:
>>> On 22/04/2023 16:07, Bernhard Beschow wrote:
>>> 
>>>> isa_get_irq() asks for an ISADevice which piix-ide doesn't provide.
>>>> Passing a NULL pointer works but causes the isabus global to be used
>>>> then. By fishing out TYPE_ISA_BUS from the QOM tree it is possible to
>>>> achieve the same as using isa_get_irq().
>>>> 
>>>> This is an alternative solution to commit 9405d87be25d 'hw/ide: Fix
>>>> crash when plugging a piix3-ide device into the x-remote machine' which
>>>> allows for cleaning up the ISA API while keeping PIIX IDE functions
>>>> user-createable.
>>>> 
>>>> Signed-off-by: Bernhard Beschow <shentey@gmail.com>
>>>> ---
>>>>    hw/ide/piix.c | 23 ++++++++++++++++++++---
>>>>    1 file changed, 20 insertions(+), 3 deletions(-)
>>>> 
>>>> diff --git a/hw/ide/piix.c b/hw/ide/piix.c
>>>> index 6942b484f9..a3a15dc7db 100644
>>>> --- a/hw/ide/piix.c
>>>> +++ b/hw/ide/piix.c
>>>> @@ -104,7 +104,8 @@ static void piix_ide_reset(DeviceState *dev)
>>>>        pci_set_byte(pci_conf + 0x20, 0x01);  /* BMIBA: 20-23h */
>>>>    }
>>>>    -static bool pci_piix_init_bus(PCIIDEState *d, unsigned i, Error **errp)
>>>> +static bool pci_piix_init_bus(PCIIDEState *d, unsigned i, ISABus *isa_bus,
>>>> +                              Error **errp)
>>>>    {
>>>>        static const struct {
>>>>            int iobase;
>>>> @@ -124,7 +125,8 @@ static bool pci_piix_init_bus(PCIIDEState *d, unsigned 
>>>> i, Error **errp)
>>>>                             object_get_typename(OBJECT(d)), i);
>>>>            return false;
>>>>        }
>>>> -    ide_bus_init_output_irq(&d->bus[i], isa_get_irq(NULL, 
>>>> port_info[i].isairq));
>>>> +    ide_bus_init_output_irq(&d->bus[i],
>>>> +                            isa_bus_get_irq(isa_bus, 
>>>> port_info[i].isairq));
>>> 
>>> I don't think is the right solution here, since ultimately we want to move 
>>> the IRQ routing out of the device itself and into the PCI-ISA bridge. I'd 
>>> go for the same solution as you've done for VIA IDE in patch 2, i.e. update 
>>> the PIIX interrupt handler to set the legacy_irqs in PCIIDEState, and then 
>>> wire them up to the ISA IRQs 14 and 15 similar to as Phil as done in his 
>>> patches:
>> 
>> The problem is user-creatable PIIX-IDE. IMO we should stick to our 
>> deprecation process before going this step because this will break it.
>
>Thomas posted some links from previous discussions where it seems that this 
>hack is still in use:
>
>https://lists.nongnu.org/archive/html/qemu-block/2019-07/msg00780.html
>https://lists.gnu.org/archive/html/qemu-block/2021-04/msg00746.html
>
>So it seems we can't even deprecate this, as it's working around missing 
>functionality in q35 :(
>
>Certainly it seems that we should add a check that will fail the machine if 
>there is more than one -device piix3-ide on the command line, since I can't 
>see that could ever work properly.
>
>I'm leaning towards adding a device property that must be set to enabled in 
>order for PIIX IDE realize() to succeed, leave it disabled by default and only 
>enable it for the q35 machine. Does that seem like a reasonable solution?

I'd rather declare this to be out of scope of this series. First, this series 
contains a lot of material already. Second, this patch attempts to preserve 
current behavior.

This patch is actually a preparation for the next one. In the next patch the 
(non-obvious) check for presence of the ISABus get removed so we need this 
patch to preserve behavior. Otherwise machines without an ISA bus will crash if 
piix3-ide gets user-created. One machine that would crash is the "remote" 
machine IIRC.

Best regards,
Bernhard

>
>>> https://patchew.org/QEMU/20230302224058.43315-1-philmd@linaro.org/20230302224058.43315-4-philmd@linaro.org/
>>> 
>>> https://patchew.org/QEMU/20230302224058.43315-1-philmd@linaro.org/20230302224058.43315-5-philmd@linaro.org/
>>> 
>>> This also reminds me, given that the first patch above is doing wiring in 
>>> pc_init1() then we are still missing part of your tidy-up series :/
>>> 
>>>>        bmdma_init(&d->bus[i], &d->bmdma[i], d);
>>>>        ide_bus_register_restart_cb(&d->bus[i]);
>>>> @@ -136,14 +138,29 @@ static void pci_piix_ide_realize(PCIDevice *dev, 
>>>> Error **errp)
>>>>    {
>>>>        PCIIDEState *d = PCI_IDE(dev);
>>>>        uint8_t *pci_conf = dev->config;
>>>> +    ISABus *isa_bus;
>>>> +    bool ambiguous;
>>>>          pci_conf[PCI_CLASS_PROG] = 0x80; // legacy ATA mode
>>>>          bmdma_init_ops(d, &piix_bmdma_ops);
>>>>        pci_register_bar(dev, 4, PCI_BASE_ADDRESS_SPACE_IO, &d->bmdma_ops);
>>>>    +    isa_bus = ISA_BUS(object_resolve_path_type("", TYPE_ISA_BUS, 
>>>> &ambiguous));
>>>> +    if (ambiguous) {
>>>> +        error_setg(errp,
>>>> +                   "More than one ISA bus found while %s supports only 
>>>> one",
>>>> +                   object_get_typename(OBJECT(d)));
>>>> +        return;
>>>> +    }
>>>> +    if (!isa_bus) {
>>>> +        error_setg(errp, "No ISA bus found while %s requires one",
>>>> +                   object_get_typename(OBJECT(d)));
>>>> +        return;
>>>> +    }
>>> 
>>> Again I think this should go away with using PCIIDEState's legacy_irqs, 
>>> since you simply let the board wire them up to the ISABus (or not) as 
>>> required.
>> 
>> Same here: This breaks user-creatable PIIX-IDE.
>> 
>>> 
>>>>        for (unsigned i = 0; i < 2; i++) {
>>>> -        if (!pci_piix_init_bus(d, i, errp)) {
>>>> +        if (!pci_piix_init_bus(d, i, isa_bus, errp)) {
>>>>                return;
>>>>            }
>>>>        }
>
>
>ATB,
>
>Mark.