lkml.org 
[lkml]   [2018]   [Aug]   [31]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
From
Date
SubjectRe: [PATCH v5 06/13] PCI/P2PDMA: Add P2P DMA driver writer's documentation


On 31/08/18 02:08 AM, Christian König wrote:
>> +One of the biggest issues is that PCI doesn't require forwarding
>> +transactions between hierarchy domains, and in PCIe, each Root Port
>> +defines a separate hierarchy domain. To make things worse, there is no
>> +simple way to determine if a given Root Complex supports this or not.
>> +(See PCIe r4.0, sec 1.3.1). Therefore, as of this writing, the kernel
>> +only supports doing P2P when the endpoints involved are all behind the
>> +same PCI bridge, as such devices are all in the same PCI hierarchy
>> +domain, and the spec guarantees that all transacations within the
>> +hierarchy will be routable, but it does not require routing
>> +between hierarchies.
>
> Can we add a kernel command line switch and a whitelist to enable P2P
> between separate hierarchies?

In future work, yes. But not for this patchset. This is definitely the
way I see things going, but we've chosen to start with what we've presented.

Logan

\
 
 \ /
  Last update: 2018-08-31 17:52    [W:0.155 / U:0.256 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site