Messages in this thread | | | Date | Thu, 27 Oct 2016 06:51:52 -0500 | From | Bjorn Helgaas <> | Subject | Re: [PATCH] pci: Don't set RCB bit in LNKCTL if the upstream bridge hasn't |
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On Thu, Oct 27, 2016 at 07:42:27AM +0200, Hannes Reinecke wrote: > 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.
Thanks! I can fold this into the changelog.
I assume you didn't mention a bugzilla or similar URL because this was found internally? I'd still like a clue about what this issue looks like to a user, because that helps connect future problem reports with this fix.
And I suppose that since 7a1562d4f2d0 appeared in v3.18, we maybe should consider marking the fix for stable?
Bjorn
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