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

On Fri, Nov 13, 2015 at 09:59:27AM +1100, Daniel Axtens wrote:

Gavin Shan [off-list ref] writes:

quoted

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 <redacted>

Thanks,
Gavin

Regards,
Daniel Axtens

quoted

Signed-off-by: Gavin Shan <redacted>
---
 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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