[Skiboot] [PATCH v2 1/9] core/pci: Return error on invalid power state transition

[Gavin Shan]

On Thu, Oct 13, 2016 at 03:18:10PM +1100, Andrew Donnellan wrote:
>On 13/10/16 12:16, Gavin Shan wrote:
>>This returns error (OPAL_PARAMETER) when having invalid power state
>>transition requests. The invalid requests include: ON to ON, OFF to
>>OFF.
>>
>>Signed-off-by: Gavin Shan <gwshan at linux.vnet.ibm.com>
>
>What's the advantage of doing this rather than immediately returning
>OPAL_SUCCESS?
>

There are two purposes: (1) To notify the caller the invalid power state
switching; (2) After this patchset is applied, OPAL_SUCCESS will causes
an PCI topology update, which is totally unecessary if we don't have
power (hotplug) state change. This is required by surprise hotplug that
relies on interrupts caused by link up/down events, meaning we cannot
put the slot into power-off state under the situation.

Thanks,
Gavin

>>---
>> core/pcie-slot.c | 6 +++---
>> 1 file changed, 3 insertions(+), 3 deletions(-)
>>
>>diff --git a/core/pcie-slot.c b/core/pcie-slot.c
>>index 6854ef1..7fe3785 100644
>>--- a/core/pcie-slot.c
>>+++ b/core/pcie-slot.c
>>@@ -199,13 +199,13 @@ static int64_t pcie_slot_set_power_state(struct pci_slot *slot, uint8_t val)
>> 	uint32_t ecap;
>> 	uint16_t state;
>>
>>+	if (slot->power_state == val)
>>+		return OPAL_PARAMETER;
>>+
>> 	/* Drop the request if functionality doesn't exist */
>> 	if (!(slot->slot_cap & PCICAP_EXP_SLOTCAP_PWCTRL))
>> 		return OPAL_SUCCESS;
>>
>>-	if (slot->power_state == val)
>>-		return OPAL_SUCCESS;
>>-
>> 	pci_slot_set_state(slot, PCI_SLOT_STATE_SPOWER_START);
>> 	slot->power_state = val;
>> 	ecap = pci_cap(pd, PCI_CFG_CAP_ID_EXP, false);
>>
>
>-- 
>Andrew Donnellan              OzLabs, ADL Canberra
>andrew.donnellan at au1.ibm.com  IBM Australia Limited