Re: [Qemu-ppc] [PATCH 3/3] spapr: introduce a fixed IRQ number space

[Cédric Le Goater]

On 06/18/2018 02:46 PM, Greg Kurz wrote:
> On Mon, 18 Jun 2018 13:31:26 +0200
> Cédric Le Goater <address@hidden> wrote:
> 
>> On 06/18/2018 11:54 AM, Greg Kurz wrote:
>>> On Mon, 18 Jun 2018 10:56:55 +0200
>>> Cédric Le Goater <address@hidden> wrote:
>>>   
>>>> [ ... ]
>>>>  
>>>>>>> This is 4 irqs per PHB, hence up to 32 PHBs. Cool, we're currently
>>>>>>> limited to 31 PHBs.
>>>>>>>       
>>>>>>>> +#define SPAPR_IRQ_MSI        0x1100  /* Offset of the dynamic range 
>>>>>>>> covered      
>>>>>>>
>>>>>>> We only support dynamic MSIs with PCI, maybe rename to 
>>>>>>> SPAPR_IRQ_PCI_MSI ?      
>>>>>>
>>>>>> hmm, no. We could have CAPI devices there. remember ? ;)
>>>>>>    
>>>>>
>>>>> Well... OpenCAPI devices are exposed to the OS as PCI devices, so I'm not
>>>>> sure we need a CAPI specific range.    
>>>>
>>>> yes. so this range is common to all devices doing dynamic allocation
>>>> of IRQs. How should we call it ? 
>>>>  
>>>>>>>> +                                      * by the bitmap allocator */    
>>>>>>>>   
>>>>>>>
>>>>>>> The range size is hence 1k (XICS_IRQS_SPAPR) for the time being.      
>>>>>>
>>>>>> in fact we could this bogus limit and use spapr->irq_map_nr now.
>>>>>>    
>>>>>
>>>>> "we could *missing verb* this bogus limit"... so I'm not sure to
>>>>> understand...    
>>>>
>>>> oups. We could use spapr->irq_map_nr instead of XICS_IRQS_SPAPR when
>>>> defining : 
>>>>
>>>>     _FDT(fdt_setprop_cell(fdt, bus_off, "ibm,pe-total-#msi", 
>>>> XICS_IRQS_SPAPR));
>>>>
>>>> in spapr_pci.c
>>>>  
>>>
>>> Ah... yeah, I've always found weird that all PHBs advertise the same number
>>> of available MSIs as the total number of irqs for the whole machine. And
>>> putting spapr->irq_map_nr looks weird all the same if all PHBs rely on the
>>> same bitmap actually.
>>>
>>> I'm thinking of doing the other way around: keep XICS_IRQS_SPAPR in
>>> "ibm,pe-total-#msi" and have one XICS_IRQS_SPAPR sized bitmap per PHB.  
>>
>> That could be the place where to put the msi allocator.
>>
> 
> Are you suggesting to move @irq_map and @irq_map_nr to sPAPRPHBState and
> to have these setup during PHB realize ? I guess we could do that.

Hmm, I think it's better to keep it under the machine. We only need 
to define an IRQ number "quantity" per phb and not a specific IRQ 
number range. The claimed numbers can be machine wide numbers.  

C.