linux-kernel - Re: [PATCH] pci: Don't set RCB bit in LNKCTL if the upstream bridge hasn't

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Date:   Thu, 27 Oct 2016 14:06:39 +0200
From:   Hannes Reinecke <hare@...e.de>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Johannes Thumshirn <jthumshirn@...e.de>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Yinghai Lu <yinghai@...nel.org>, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pci: Don't set RCB bit in LNKCTL if the upstream bridge
 hasn't

On 10/27/2016 01:51 PM, Bjorn Helgaas wrote:
> 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.
> 
We do have a bugzilla report, but as this is a) on the SUSE internal
bugzilla and b) a customer issue I didn't include a reference here.

However, the symptoms are:

[    8.648872] mlx4_core: Mellanox ConnectX core driver v2.2-1 (Feb, 2014)
[    8.648889] mlx4_core: Initializing 0000:41:00.0
[   10.068642] mlx4_core 0000:41:00.0: command 0xfff failed: fw status = 0x1
[   10.068645] mlx4_core 0000:41:00.0: MAP_FA command failed, aborting
[   10.068659] mlx4_core 0000:41:00.0: Failed to start FW, aborting
[   10.068661] mlx4_core 0000:41:00.0: Failed to init fw, aborting.
[   11.071536] mlx4_core: probe of 0000:41:00.0 failed with error -5

> And I suppose that since 7a1562d4f2d0 appeared in v3.18, we maybe
> should consider marking the fix for stable?
> 
Yes, please.

Cheers,

Hannes
-- 
Dr. Hannes Reinecke		   Teamlead Storage & Networking
hare@...e.de			               +49 911 74053 688
SUSE LINUX GmbH, Maxfeldstr. 5, 90409 Nürnberg
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