[Skiboot] [PATCH v2] phb4: Enable PCI peer-to-peer

Frederic Barrat fbarrat at linux.vnet.ibm.com
Mon Jul 17 06:04:57 AEST 2017

Le 12/07/2017 à 17:38, Benjamin Herrenschmidt a écrit :
>> +	/*
>> +	 * On p9, loads are only supported if initiator and target
>> +	 * devices are on the same PHB.
>> +	 */
>> +	if ((desc & OPAL_PCI_P2P_LOAD) && (phb_init != phb_target))
>> +		return OPAL_UNSUPPORTED;
> If they are under the same PHB you don't need any of the other stuff
> either... ie, the P2P accesses won't ever be visible to the PHB itself.
> You*might*  need however to enable P2P in the switches.
> In fact for the "same PHB" case you don't need to check if they have a
> set_p2p callback.

Thanks, Ben

Intermediate switches... I'm getting more than I bargained for here.

The pressing need we have for p2p doesn't involve a setup with 2 devices 
under the same PHB, so I'm thinking maybe I should skip it for now, but 
I'd like to at least understand what would be required. google tells me 
I need to find a pci spec about ACS, is that right? Do you have it? Am I 
entering a world of pain?


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