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Re: [Qemu-ppc] [Qemu-devel] [PATCH] spapr-pci: rework MSI/MSIX

From: Alexey Kardashevskiy
Subject: Re: [Qemu-ppc] [Qemu-devel] [PATCH] spapr-pci: rework MSI/MSIX
Date: Fri, 23 Aug 2013 13:10:30 +1000
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130625 Thunderbird/17.0.7

On 08/01/2013 09:22 AM, Anthony Liguori wrote:
> Alexey Kardashevskiy <address@hidden> writes:
>> On 08/01/2013 04:02 AM, Anthony Liguori wrote:
>>> Alexey Kardashevskiy <address@hidden> writes:
>>>> On the sPAPR platform a guest allocates MSI/MSIX vectors via RTAS
>>>> hypercalls which return global IRQ numbers to a guest so it only
>>>> operates with those and never touches MSIMessage.
>>>> Therefore MSIMessage handling is completely hidden in QEMU.
>>>> Previously every sPAPR PCI host bridge implemented its own MSI window
>>>> to catch msi_notify()/msix_notify() calls from QEMU devices (virtio-pci
>>>> or vfio) and route them to the guest via qemu_pulse_irq().
>>>> MSIMessage used to be encoded as:
>>>>    .addr - address within the PHB MSI window;
>>>>    .data - the device index on PHB plus vector number.
>>>> The MSI MR write function translated this MSIMessage to a global IRQ
>>>> number and called qemu_pulse_irq().
>>>> However the total number of IRQs is not really big (at the moment it is
>>>> 1024 IRQs starting from 4096) and even 16bit data field of MSIMessage
>>>> seems to be enough to store an IRQ number there.
>>>> This simplifies MSI handling in sPAPR PHB. Specifically, this does:
>>>> 1. remove a MSI window from a PHB;
>>>> 2. add a single memory region for all MSIs to sPAPREnvironment
>>>> and spapr_pci_msi_init() to initialize it;
>>>> 3. encode MSIMessage as:
>>>>     * .addr - a fixed address of SPAPR_PCI_MSI_WINDOW==0x40000000000ULL;
>>>>     * .data as an IRQ number.
>>>> 4. change IRQ allocator to align first IRQ number in a block for MSI.
>>>> MSI uses lower bits to specify the vector number so the first IRQ has to
>>>> be aligned. MSIX does not need any special allocator though.
>>>> Signed-off-by: Alexey Kardashevskiy <address@hidden>
>>> Reviewed-by: Anthony Liguori <address@hidden>
>>> Does this actually fix any bug or is this just refactoring?  If it's the
>>> later, it'll have to wait until after the 1.7 window opens up.
>> This is refactoring which should make IRQFD enablement on spapr
>> easier.
> Okay, I'll apply it after hard freeze then.

Anyone, ping?


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