Re: [Qemu-devel] [PATCH 11/15] apb: split pci_pbm_map_irq() into separate functions for bus A and bus B

[Artyom Tarasenko <atar4qemu@gmail.com>]

On Sun, Dec 17, 2017 at 12:09 PM, Mark Cave-Ayland
<mark.cave-ayland@ilande.co.uk> wrote:
> On 19/11/17 11:06, Mark Cave-Ayland wrote:
>
>> On 17/11/17 14:33, Artyom Tarasenko wrote:
>>
>>> On Fri, Nov 17, 2017 at 2:42 PM, Mark Cave-Ayland
>>> <mark.cave-ayland@ilande.co.uk> wrote:
>>>>
>>>> After the previous refactoring it is now possible to use separate
>>>> functions
>>>> to improve clarity of the interrupt paths. Similarly by checking the PCI
>>>> devnfn to identify busA during apb_pci_bridge_realize() it becomes
>>>> possible
>>>> to completely remove the busA property from the PBMPCIBridge state.
>>>>
>>>> Signed-off-by: Mark Cave-Ayland <mark.cave-ayland@ilande.co.uk>
>>>> ---
>>>>   hw/pci-host/apb.c         |   54
>>>> ++++++++++++++++++---------------------------
>>>>   include/hw/pci-host/apb.h |    3 ---
>>>>   2 files changed, 21 insertions(+), 36 deletions(-)
>>>>
>>>> diff --git a/hw/pci-host/apb.c b/hw/pci-host/apb.c
>>>> index 6c20285..268100e 100644
>>>> --- a/hw/pci-host/apb.c
>>>> +++ b/hw/pci-host/apb.c
>>>> @@ -517,32 +517,27 @@ static int pci_apb_map_irq(PCIDevice *pci_dev, int
>>>> irq_num)
>>>>       return irq_num;
>>>>   }
>>>>
>>>> -static int pci_pbm_map_irq(PCIDevice *pci_dev, int irq_num)
>>>> +static int pci_pbmA_map_irq(PCIDevice *pci_dev, int irq_num)
>>>>   {
>>>> -    PBMPCIBridge *br = PBM_PCI_BRIDGE(pci_bridge_get_device(
>>>> -
>>>> PCI_BUS(qdev_get_parent_bus(DEVICE(pci_dev)))));
>>>> -
>>>> -    int bus_offset;
>>>> -    if (br->busA) {
>>>> -        bus_offset = 0x0;
>>>> +    /* The on-board devices have fixed (legacy) OBIO intnos */
>>>> +    switch (PCI_SLOT(pci_dev->devfn)) {
>>>> +    case 1:
>>>> +        /* Onboard NIC */
>>>> +        return 0x21;
>>>> +    case 3:
>>>> +        /* Onboard IDE */
>>>> +        return 0x20;
>>>> +    default:
>>>> +        /* Normal intno, fall through */
>>>> +        break;
>>>> +    }
>>>>
>>>> -        /* The on-board devices have fixed (legacy) OBIO intnos */
>>>> -        switch (PCI_SLOT(pci_dev->devfn)) {
>>>> -        case 1:
>>>> -            /* Onboard NIC */
>>>> -            return 0x21;
>>>> -        case 3:
>>>> -            /* Onboard IDE */
>>>> -            return 0x20;
>>>> +    return ((PCI_SLOT(pci_dev->devfn) << 2) + irq_num) & 0x1f;
>>>> +}
>>>>
>>>> -        default:
>>>> -            /* Normal intno, fall through */
>>>> -            break;
>>>> -        }
>>>> -    } else {
>>>> -        bus_offset = 0x10;
>>>> -    }
>>>> -    return (bus_offset + (PCI_SLOT(pci_dev->devfn) << 2) + irq_num) &
>>>> 0x1f;
>>>> +static int pci_pbmB_map_irq(PCIDevice *pci_dev, int irq_num)
>>>> +{
>>>> +    return (0x10 + (PCI_SLOT(pci_dev->devfn) << 2) + irq_num) & 0x1f;
>>>>   }
>>>>
>>>>   static void pci_apb_set_irq(void *opaque, int irq_num, int level)
>>>> @@ -593,7 +588,7 @@ static void apb_pci_bridge_realize(PCIDevice *dev,
>>>> Error **errp)
>>>>
>>>>       /* If initialising busA, ensure that we allow IO transactions so
>>>> that
>>>>          we get the early serial console until OpenBIOS configures the
>>>> bridge */
>>>> -    if (br->busA) {
>>>> +    if (dev->devfn == PCI_DEVFN(1, 1)) {
>>>
>>>
>>> I think the previous syntax was more explicit here. A comment would be
>>> nice.
>>
>>
>> Yes it's definitely something that isn't immediately obvious, which is
>> why I left the above comment in place explaining what the if() branch is
>> doing. Is there something in the comment that isn't particularly clear?
>>
>> Note one of the reasons for wanting to remove the busA property is that
>> where possible I'd like to reduce the code in the IRQ path, and while
>> the existing code works I am still unsure of the additional overhead of
>> the 2 levels of QOM type checking that the current approach requires for
>> each IRQ.
>
>
> Hi Artyom,
>
> Thinking about this a bit more during freeze, this is actually doing the
> opposite of what we want, as it requires the device realise function to
> behave differently depending upon how it is related to the PCI bus.
>
> How about swapping this out for a qdev bool property for APB named
> "enable-early-pci-io-access", setting it just for the PCI_DEVFN(1, 1) device
> containing the ebus and then alter the if() statement above to enable PCI IO
> access if the qdev property is set?

This does sound reasonable. I wonder if this has to be a qdev property though.
Doesn't the physical bridge have a software visible bit/register for it?


-- 
Regards,
Artyom Tarasenko

SPARC and PPC PReP under qemu blog: http://tyom.blogspot.com/search/label/qemu