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

Daniel Axtens
2015-11-12T22:59:49Z

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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.

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

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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