Hi,
On 11/28/19 5:43 PM, Andre Przywara wrote:
> On Mon, 25 Nov 2019 10:30:22 +0000
> Alexandru Elisei <alexandru.elisei@xxxxxxx> wrote:
>
>> The "bus-range" property encodes the first and last bus number. kvmtool
>> uses bus 0 for PCI and bus 1 for MMIO.
> Mmmh, but this DT setting is about (guest visible) PCI busses, not kvmtool busses, isn't it?
You are correct, this setting is about guest visible PCI busses, not kvmtool
buses, I got the two confused.
> So for the PCI devices we *emulate* that's probably correct, since we don't have any PCI bridge functionality among them, but wouldn't forwarding a PCI device with a bridge require more than one bus? And the guest OS' enumeration code would try to create a new bus, but fails, because there is only one?
>
> So I agree that the [0, 1] looks somewhat arbitrary, but shouldn't we set it to [0, 255] instead, to not limit things?
> I think this setting should correspond to the PCIe config space size we provide, which should be: 4096 bytes * 8 fns * 32 devs * nr_busses (for PCIe).
kvmtool emulates a single bus, bus 0. Whenever the PCI code searches for a device,
it searches using the device number, not a tuple (bus_number, device_number) (take
a look at pci__config_{rd,wr}). Also, in pci_device_exists, it compares the bus
number and function number against 0, the default values from
pci_config_address_bits. On the other hand, kvmtool doesn't emulate any bridges,
so after probing bus 0, Linux won't try to probe any other buses. So regardless of
the bus-range property, Linux will only probe bus 0.
>From a correctness point of view, I think <0,0> is the right value here as it
matches what kvmtool emulates. What do you think?
Thanks,
Alex
>
> At least that's my understanding of these things, please correct me if I am wrong.
>
> Cheers,
> Andre.
>
>> Advertise only the PCI bus in
>> the PCI DT node by setting "bus-range" to <0, 0>.
>>
>> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
>> ---
>> arm/pci.c | 2 +-
>> 1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/arm/pci.c b/arm/pci.c
>> index 557cfa98938d..ed325fa4a811 100644
>> --- a/arm/pci.c
>> +++ b/arm/pci.c
>> @@ -30,7 +30,7 @@ void pci__generate_fdt_nodes(void *fdt)
>> struct of_interrupt_map_entry irq_map[OF_PCI_IRQ_MAP_MAX];
>> unsigned nentries = 0;
>> /* Bus range */
>> - u32 bus_range[] = { cpu_to_fdt32(0), cpu_to_fdt32(1), };
>> + u32 bus_range[] = { cpu_to_fdt32(0), cpu_to_fdt32(0), };
>> /* Configuration Space */
>> u64 cfg_reg_prop[] = { cpu_to_fdt64(KVM_PCI_CFG_AREA),
>> cpu_to_fdt64(ARM_PCI_CFG_SIZE), };
