On 10/26/2016 09:43 PM, Bjorn Helgaas wrote:
> Hi Johannes,
>
> On Wed, Oct 26, 2016 at 03:53:34PM +0200, Johannes Thumshirn wrote:
>> The Read Completion Boundary bit must only be set on a device or endpoint if
>> it is set on the upstream bridge.
>>
>> Fixes: 7a1562d4f ("PCI: Apply _HPX Link Control settings to all devices with a link")
>
> Can you please include a spec citation and a pointer to the bug report?
>
PCI Express Base Specification 1.1,
section 2.3.1.1. Data Return for Read Requests:
The Read Completion Boundary (RCB) parameter determines the naturally
aligned address boundaries on which a Read Request may be serviced with
multiple Completions
o For a Root Complex, RCB is 64 bytes or 128 bytes
o This value is reported through a configuration register
(see Section 7.8)
Note: Bridges and Endpoints may implement a corresponding command
bit which may be set by system software to indicate the RCB value
for the Root Complex, allowing the Bridge/Endpoint to optimize its
behavior when the Root Complex’s RCB is 128 bytes.
o For all other system elements, RCB is 128 bytes
In this particular case the _HPX method was causing the RCB for all PCI
devices to be set to 128 bytes, while the root bridge remained at 64 bytes.
While this is arguably a BIOS bug, earlier linux version (ie without the
mentioned patch) were running fine, so this is actually a regression.
Cheers,
Hannes
--
Dr. Hannes Reinecke Teamlead Storage & Networking
hare@xxxxxxx +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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HRB 21284 (AG Nürnberg)
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