Re: [bugzilla-daemon@bugzilla.kernel.org: [Bug 208507] New: BISECTED: i2c timeout loading module ddbridge with commit d2345d1231d80ecbea5fb764eb43123440861462]

[Bjorn Helgaas <helgaas@kernel.org>]

[+cc Salvatore, Mauro, Daniel, linux-media]

On Thu, Jul 09, 2020 at 02:17:22PM -0500, Bjorn Helgaas wrote:
> Bisected to Debian commit d2345d1231d8, which is a backport of the
> upstream commit b88bf6c3b6ff ("PCI: Add boot interrupt quirk mechanism
> for Xeon chipsets").
> 
> Reporter confirmed that reverting the Debian backport from 4.19.132
> fixes the problem.
>
> ----- Forwarded message from bugzilla-daemon@bugzilla.kernel.org -----
> 
> Date: Thu, 09 Jul 2020 15:01:11 +0000
> From: bugzilla-daemon@bugzilla.kernel.org
> To: bjorn@helgaas.com
> Subject: [Bug 208507] New: BISECTED: i2c timeout loading module ddbridge with
> 	commit d2345d1231d80ecbea5fb764eb43123440861462
> Message-ID: <bug-208507-41252@https.bugzilla.kernel.org/>
> 
> https://bugzilla.kernel.org/show_bug.cgi?id=208507
> 
>             Bug ID: 208507
>            Summary: BISECTED: i2c timeout loading module ddbridge with
>                     commit d2345d1231d80ecbea5fb764eb43123440861462
>            Product: Drivers
>            Version: 2.5
>     Kernel Version: 4.19.132
>           Hardware: x86-64
>                 OS: Linux
>               Tree: Mainline
>             Status: NEW
>           Severity: normal
>           Priority: P1
>          Component: PCI
>           Assignee: drivers_pci@kernel-bugs.osdl.org
>           Reporter: bernhard@turmann.eu
>         Regression: Yes
> 
> Created attachment 290179
>   --> https://bugzilla.kernel.org/attachment.cgi?id=290179&action=edit
> dmesg on 4.19.132
> 
> OS: Debian 10.4 Buster
> CPU: Intel(R) Xeon(R) CPU D-1541 @ 2.10GHz
> Hardware: Supermicro  Super Server
> Mainboard: Supermicro X10SDV
> DVB card: Digital Devices Cine S2 V7 Advanced DVB adapter
> 
> Issue:
> =====
> Loading kernel module ddbridge fails with i2c timeouts, see attached dmesg. The
> dvb media adapter is unusable.
> This happened after Linux kernel upgrade from 4.19.98-1+deb10u1 to
> 4.19.118-2+deb10u1.
> 
> A git bisect based on the Debian kernel repo on branch buster identified as
> first bad commit: [1fb0eb795661ab9e697c3a053b35aa4dc3b81165] Update to
> 4.19.116.
> 
> Another git bisect based on upstream Linux kernel repo on branch v4.19.y
> identified as first bad commit: [d2345d1231d80ecbea5fb764eb43123440861462] PCI:
> Add boot interrupt quirk mechanism for Xeon chipsets.
> 
> Other affected Debian kernel version: 5.6.14+2~bpo10+1
> I tested this version via buster-backports, because so far I was unable to
> build my own kernel from 5.6.y or even 5.7.y.
> 
> Workaround:
> ==========
> Reverting the mentioned commit d2345d1231d80ecbea5fb764eb43123440861462 on top
> of 4.19.132 is fixing the problem. Reverting the same commit on 4.19.118 or
> 4.19.116 is also fixing the problem.

Sorry, I dropped the ball on this.

Berni has verified that this problem still exists in v6.1.4, and has
attached current dmesg logs and lspci output.  

Sean's comment (https://bugzilla.kernel.org/show_bug.cgi?id=208507#c18)
suggests this is actually a ddbridge driver issue related to INTx
emulation or MSI support.

Berni confirmed that the i2c timeouts happen when
CONFIG_DVB_DDBRIDGE_MSIENABLE is not enabled, and that enabling MSI
via the "ddbridge.msi=1" module parameter avoids the i2c timeouts.

The Kconfig help for DVB_DDBRIDGE_MSIENABLE:

  Use PCI MSI (Message Signaled Interrupts) per default. Enabling this
  might lead to I2C errors originating from the bridge in conjunction
  with certain SATA controllers, requiring a reload of the ddbridge
  module. MSI can still be disabled by passing msi=0 as option, as
  this will just change the msi option default value.

suggests that there may be an i2c or SATA issue that could be fixed so
ddbridge MSI could be always enabled.  But I don't know about that
underlying issue.

Per MAINTAINERS, the ddbridge driver looks orphaned, so I cc'd the
media folks and Daniel, who might know something about the MSI issues,
based on adaf4df70521 ("media: ddbridge: Kconfig option to control the
MSI modparam default").

Bjorn