[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Qemu-devel] [PATCH 1/2] pci: Add pci_device_get_host_irq

From: Jan Kiszka
Subject: Re: [Qemu-devel] [PATCH 1/2] pci: Add pci_device_get_host_irq
Date: Fri, 01 Jun 2012 14:52:56 +0200
User-agent: Mozilla/5.0 (X11; U; Linux i686 (x86_64); de; rv: Gecko/20080226 SUSE/ Thunderbird/ Mnenhy/

On 2012-05-30 22:31, Michael S. Tsirkin wrote:
>>> So we'll just have PIIX_NUM_PIC_IRQS entries there and use
>>> irq_count instead of the pic_levels bitmap.
>> Just that this affects generic PCI code, not only PIIX-specific things.
> Yes but it's not a problem - pci_bus_irqs sets the map function and nirqs.
>> And that we need to save/restore some irq_count field according to the
>> old semantics.
> Well, it's a bug: this is redundant info we should not have exposed it.
> Anyway, let's make the rest work properly and cleanly first, add a FIXME
> for now, then we'll find a hack making it work for migration.

It remains non-trivial: I got your patch working (a minor init issue),
but yet without changing the number of IRQs for PIIX3, so keeping the
irq_count semantics for this host bridge.

Now I'm facing three possibilities of how to proceed:

1. Give up on the (currently broken) feature to write a vmstate for
   older QEMU versions.

   This will allow to declare the irq_count field in vmstate_pcibus
   unused, and we would have to restore it on vmload step-wise via the
   PCI devices. It would also allow to change its semantics for PIIX3,
   mapping directly to PIC IRQs.

2. Keep writing a legacy irq_count field.

   This will require quite a few new APIs so that host bridges that
   want to change their nirq can still generate a compatible irq_count
   vmstate field. Namely:
    - A function to set up vmstate_irq_count and define a callback that
      the core will invoke to prepare the vmstate_irq_count before
    - A function to obtain the IRQ mapping /without/ the final host
      bridge step. This is required so that the callback above can
      calculate the old state like in the PIIX3 case.

3. Keep irq_count and nirq as is, introduce additional map_host_irq.

   This is simpler than 2 and more compatible than 1. It would also
   allow to introduce the polarity and masking information more
   smoothly as we won't have to add it to existing map_irq callbacks

Any other suggestions?


Siemens AG, Corporate Technology, CT T DE IT 1
Corporate Competence Center Embedded Linux

reply via email to

[Prev in Thread] Current Thread [Next in Thread]