Re: [PATCH v7 38/50] powerpc/powernv: Exclude root bus in pnv_pci_reset_secondary_bus()

Gavin Shan
2015-11-12T23:26:54Z

On Fri, Nov 13, 2015 at 09:59:27AM +1100, Daniel Axtens wrote:
>Gavin Shan <gwshan@linux.vnet.ibm.com> writes:
>
>> When pnv_pci_reset_secondary_bus() is called to issue reset on
>> the indicated secondary bus, the bus can't be root bus. So we
>> needn't consider root bus in the function.
>
>It took me a while to convince myself that this is correct. For the
>record, this is why it's correct:
>
>pnv_pci_reset_secondary_bus fills the reset_secondary_bus callback in
>the pci_controller_ops structure, and isn't used elsewhere.
>
>In arch/powerpc/kernel/pci.c, that callback is called (if it exists) in
>pcibios_reset_secondary_bus(). It's not called anywhere else.
>
>The PPC pcibios_reset_secondary_bus overrides the weak version in
>drivers/pci/pci.c. It's called from the same file by
>pci_reset_bridge_secondary_device() (and nowhere else).
>
>pci_reset_bridge_secondary_device() is nicely documented:
>
>/**
> * pci_reset_bridge_secondary_bus - Reset the secondary bus on a PCI bridge.
> * @dev: Bridge device
> *
> * Use the bridge control register to assert reset on the secondary bus.
> * Devices on the secondary bus are left in power-on state.
> */
>
>Therefore, by the definiton of pci_reset_bridge_secondary_bus,
>pnv_pci_reset_secondary_bus() can only be called with a bridge
>device. As such, a bridge reset only is appropriate. If this breaks
>anything, the caller is broken.
>
>It might be worth including a condensed version of this in the commit
>message.
>

Right. I'll add more description to the changelog in next revision.

>Reviewed-by: Daniel Axtens <dja@axtens.net>
>

Thanks,
Gavin

>Regards,
>Daniel Axtens
>
>>
>> Signed-off-by: Gavin Shan <gwshan@linux.vnet.ibm.com>
>> ---
>> arch/powerpc/platforms/powernv/eeh-powernv.c | 12 ++----------
>> 1 file changed, 2 insertions(+), 10 deletions(-)
>>
>> diff --git a/arch/powerpc/platforms/powernv/eeh-powernv.c b/arch/powerpc/platforms/powernv/eeh-powernv.c
>> index a7d84a4..c69b6a1 100644
>> --- a/arch/powerpc/platforms/powernv/eeh-powernv.c
>> +++ b/arch/powerpc/platforms/powernv/eeh-powernv.c
>> @@ -880,16 +880,8 @@ static int pnv_eeh_bridge_reset(struct pci_dev *dev, int option)
>>
>> void pnv_pci_reset_secondary_bus(struct pci_dev *dev)
>> {
>> - struct pci_controller *hose;
>> -
>> - if (pci_is_root_bus(dev->bus)) {
>> - hose = pci_bus_to_host(dev->bus);
>> - pnv_eeh_root_reset(hose, EEH_RESET_HOT);
>> - pnv_eeh_root_reset(hose, EEH_RESET_DEACTIVATE);
>> - } else {
>> - pnv_eeh_bridge_reset(dev, EEH_RESET_HOT);
>> - pnv_eeh_bridge_reset(dev, EEH_RESET_DEACTIVATE);
>> - }
>> + pnv_eeh_bridge_reset(dev, EEH_RESET_HOT);
>> + pnv_eeh_bridge_reset(dev, EEH_RESET_DEACTIVATE);
>> }
>>
>> /**
>> --
>> 2.1.0
>>
>> --
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