linux-kernel - Re: [PATCH v8 11/14] PCI/RCEC: Add RCiEP's linked RCEC to AER/ERR

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Message-ID: <d023cc5153bf855e27d7ee098e1afa0fd5ba9761.camel@intel.com>
Date:   Tue, 13 Oct 2020 09:55:34 -0700
From:   Sean V Kelley <sean.v.kelley@...el.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     "Zhuo, Qiuxu" <qiuxu.zhuo@...el.com>,
        "Jonathan.Cameron@...wei.com" <Jonathan.Cameron@...wei.com>,
        "Kuppuswamy, Sathyanarayanan" <sathyanarayanan.kuppuswamy@...el.com>,
        "Raj, Ashok" <ashok.raj@...el.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "seanvk.dev@...gontracks.org" <seanvk.dev@...gontracks.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>
Subject: Re: [PATCH v8 11/14] PCI/RCEC: Add RCiEP's linked RCEC to AER/ERR

On Mon, 2020-10-12 at 17:58 -0500, Bjorn Helgaas wrote:
> On Fri, Oct 09, 2020 at 11:51:39PM +0000, Kelley, Sean V wrote:
> > On Fri, 2020-10-09 at 15:07 -0700, Sean V Kelley wrote:
> > So I tested the following out, including your moving flr to aer.c:
> > 
> > - Renamed flr_on_rciep() to flr_on_rc() for RC devices (RC_END and
> > RC_EC)
> > 
> > - Moved check on dev->rcec into aer_root_reset() including the FLR.
> > 
> > - Reworked pci_walk_bridge() to drop extra dev argument and check
> > locally for the bridge->rcec. Maybe should also check on type when
> > checking on bridge->rcec.
> > 
> > Note I didn't use the check on aer_cap existence because I think
> > you
> > had added that for simply being able to skip over for the non-
> > native
> > case and I handle that with the single goto at the beginning which
> > takes you to the FLR.
> 
> Right.  Well, my thinking was that "root" would be a device with the
> AER Root Error Command and Root Error Status registers, i.e., a Root
> Port or RCEC.  IIUC that basically means the APEI case where firmware
> gives us an error record.

Got it.

> 
> Isn't the existing v5.9 code buggy in that it unconditionally pokes
> these registers?  I think the APEI path can end up here, and firmware
> probably has not granted us control over AER.

Yes, APEI path can end up here even in the absence of AER control.

> 
> Somewhat related question: I'm a little skeptical about the fact that
> aer_root_reset() currently does:
> 
>   - clear ROOT_PORT_INTR_ON_MESG_MASK
>   - do reset
>   - clear PCI_ERR_ROOT_STATUS
>   - enable ROOT_PORT_INTR_ON_MESG_MASK

It's a bit of a mix and growing with RC_END handling.

> 
> In the APEI path all this AER register manipulation must be done by
> firmware before passing the error record to the OS.  So in the native
> case where the OS does own the AER registers, why can't the OS do
> that
> manipulation in the same order, i.e., all before doing the reset?

And you're right, the mix here imposes additional complexity for native
versus non-native. If you're not actively engaged with the code, it's
not obvious. So, yes moving it out would make more sense.


> 
> > So this is rough, compiled, tested with AER injections but that's
> > it...
> 
> I couldn't actually apply the patch below because it seems to be
> whitespace-damaged, but I think I like it.

Yes, it was a quick copy-paste to an existing email. Will work with
your branch.

> 
>   - It would be nice to be able to just call pcie_flr() and not have
>     to add flr_on_rc().  I can't remember why we need the
>     pcie_has_flr() / pcie_flr() dance.  It seems racy and ugly, but I
>     have a vague recollection that there actually is some reason for
>     it.

I'll have a look.

> 
>   - I would *rather* consolidate the AER register updates and test
> for
>     the non-native case once instead of treating it like a completely
>     separate path with a "goto".  But maybe not possible.  Not a big
>     deal either way.

Following your line of reasoning above, I think we can better
consolidate the AER register updates.

> 
>   - Getting rid of the extra "dev" argument to pci_walk_bridge() is a
>     great side-effect.  I didn't even notice that.
> 
>   - If we can simplify that "state == pci_channel_io_frozen" case as
>     this does, that is a *big* deal because there are other patches
>     just waiting to touch that reset and it will be much simpler if
>     there's only one reset_subordinate_devices() call there.

Agreed.

> 
> If you do work this up, I'd really appreciate it if you can start
> with
> my pci/err branch so I don't have to re-do all the tweaks I've
> already
> done:
> 
>   
> https://git.kernel.org/pub/scm/linux/kernel/git/helgaas/pci.git/commit/?h=pci/err
> 

Will do.

Thanks,

Sean



> Bjorn