[linuxppc-release][PATCH] powerpc/pci-hotplug: fix init issue of rescanned pci device

[Bjorn Helgaas]

On Wed, Dec 5, 2012 at 2:29 AM, Chen Yuanquan-B41889
<B41889 at freescale.com> wrote:
> On 12/05/2012 04:26 PM, Benjamin Herrenschmidt wrote:
>>
>> On Wed, 2012-12-05 at 16:20 +0800, Chen Yuanquan-B41889 wrote:
>>>
>>> On 12/05/2012 03:17 PM, Benjamin Herrenschmidt wrote:
>>>>
>>>> On Wed, 2012-12-05 at 10:31 +0800, Yuanquan Chen wrote:
>>>>>
>>>>> On powerpc arch, some fixup work of PCI/PCI-e device is just done
>>>>> during the
>>>>> first scan at booting time. For the PCI/PCI-e device rescanned after
>>>>> linux OS
>>>>> booting up, the fixup work won't be done, which leads to dma_set_mask
>>>>> error or
>>>>> irq related issue in rescanned PCI/PCI-e device's driver. So, it does
>>>>> the same
>>>>> fixup work for the rescanned device to avoid this issue.
>>>>
>>>> Hrm, the patch is a bit gross. First the code shouldn't be copy/pasted
>>>> that way but factored out.
>>
>> Please, at least format your email properly so I can try to undertand
>> without needing aspirin.
>>
>>> There's a judgement "if (!bus->is_added)" before calling of
>>> pcibios_fixup_bus in pci_scan_child_bus, so for the rescanned device,
>>> the fixup won't execute, which leads to fatal error in driver of
>>> rescanned
>>> device on freescale  powerpc, no this issues on x86 arch.
>>
>> First, none of that invalidates my statement that you shouldn't
>> duplicate a whole block of code like this. Even if your approach is
>> correct (which is debated separately), at the very least you should
>> factor the code out into a common function between the two copies.
>>
>>> Remove the judgement, let it to do the pcibios_fixup_bus
>>> directly, the error won't occur for the rescanned device. But it's
>>> general code, not proper to change here, so copy the pcibios_fixup_bus
>>> work to  pcibios_enable_device.
>>>
>>>> I'm surprised also that is_added is false when pcibios_enable_device()
>>>> gets called ... that looks strange to me. At what point is that enable
>>>> happening in the hotplug sequence ?
>>>
>>> All devices are rescanned and then call the pci_enable_devices and
>>> pci_bus_add_devices.
>>
>> Where ? How ? What is the sequence happening ? In any case, I think if
>> we need a proper fixup done per-device like that after scan we ought to
>> create a new hook at the generic level rather than that sort of hack.
>>
>
> echo 1 > rescan to trigger dev_rescan_store:
>
> dev_rescan_store->pci_rescan_bus->pci_scan_child_bus,
> pci_assign_unassigned_bus_resources,
> pci_enable_bridges, pci_bus_add_devices
>
> pci_enable_bridges->pci_enable_device->__pci_enable_device_flags->do_pci_enable_device->
> pcibios_enable_device
>
> pci_bus_add_devices->pci_bus_add_device->"dev->is_added = 1"
>
> Yeah, it's general fixup code for every rescanned PCI/PCI-e device on
> powerpc at runtime. So if
> we want to call it in a ppc_md member, we need to wrap it as a function and
> assign it in every ppc_md,
> it isn't proper for the general code.
>
> Regards,
> yuanquan
>
>
>>> The patch code will be called by pci_enable_devices. The "dev->is_added"
>>> is set in pci_bus_add_device
>>> which is called by pci_bus_add_devices. So "dev->is_added" is false when
>>> checking it in pcibios_enable_device
>>> for the rescanned device.
>>
>> Who calls pci_enable_device() in the rescan case ? Why isn't it left to
>> the driver ? I don't think we can rely on that behaviour not to change.
>>
>>>> How do you trigger the rescan anyway ?
>>>
>>> Use the interface under /sys :
>>> echo 1 > /sys/bus/pci/devices/xxx/remove
>>>
>>> then echo 1 to the pci device which is the bus of the removed device
>>> echo 1 > /sys/bus/pci/devices/xxxx/rescan
>>> the removed device will be scanned and it's driver module will be loaded
>>> automatically.
>>
>> Yeah this code path are known to be fishy. I think the problem is at the
>> generic abstraction level and that's where it needs to be fixed.
>>
>> Cheers,
>> Ben.
>>
>>> Regards,
>>> yuanquan
>>>>
>>>> I think the problem needs to be solve at a higher level, I'm adding
>>>> linux-pci & Bjorn to the CC list.
>>>>
>>>> Cheers,
>>>> Ben.
>>>>
>>>>> Signed-off-by: Yuanquan Chen <B41889 at freescale.com>
>>>>> ---
>>>>>    arch/powerpc/kernel/pci-common.c |   20 ++++++++++++++++++++
>>>>>    1 file changed, 20 insertions(+)
>>>>>
>>>>> diff --git a/arch/powerpc/kernel/pci-common.c
>>>>> b/arch/powerpc/kernel/pci-common.c
>>>>> index 7f94f76..f0fb070 100644
>>>>> --- a/arch/powerpc/kernel/pci-common.c
>>>>> +++ b/arch/powerpc/kernel/pci-common.c
>>>>> @@ -1496,6 +1496,26 @@ int pcibios_enable_device(struct pci_dev *dev,
>>>>> int mask)
>>>>>                 if (ppc_md.pcibios_enable_device_hook(dev))
>>>>>                         return -EINVAL;
>>>>>    +    if (!dev->is_added) {
>>>>> +               /*
>>>>> +                * Fixup NUMA node as it may not be setup yet by the
>>>>> generic
>>>>> +                * code and is needed by the DMA init
>>>>> +                */
>>>>> +               set_dev_node(&dev->dev, pcibus_to_node(dev->bus));
>>>>> +
>>>>> +               /* Hook up default DMA ops */
>>>>> +               set_dma_ops(&dev->dev, pci_dma_ops);
>>>>> +               set_dma_offset(&dev->dev, PCI_DRAM_OFFSET);
>>>>> +
>>>>> +               /* Additional platform DMA/iommu setup */
>>>>> +               if (ppc_md.pci_dma_dev_setup)
>>>>> +                       ppc_md.pci_dma_dev_setup(dev);
>>>>> +
>>>>> +               /* Read default IRQs and fixup if necessary */
>>>>> +               pci_read_irq_line(dev);
>>>>> +               if (ppc_md.pci_irq_fixup)
>>>>> +                       ppc_md.pci_irq_fixup(dev);
>>>>> +       }
>>>>>         return pci_enable_resources(dev, mask);
>>>>>    }

Is this the same issue Hiroo MATSUMOTO was working on earlier?
(http://comments.gmane.org/gmane.linux.ports.ppc.embedded/50080)

We went round and round on those patches (partly my fault for
excessive bike-shedding), and then we stalled out because of an
ordering issue with CardBus init and an IRQ quirk.

Here's the last status I remember:
http://marc.info/?l=linux-pci&m=135006501620378&w=2

Bjorn