linux-kernel - Re: [PATCH v9 00/14] pci: Work around ASMedia ASM2824 PCIe link training failures

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Message-ID: <20230616202900.GA1540115@bhelgaas>
Date:   Fri, 16 Jun 2023 15:29:00 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "Maciej W. Rozycki" <macro@...am.me.uk>
Cc:     linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
        Eric Dumazet <edumazet@...gle.com>,
        Oliver O'Halloran <oohall@...il.com>,
        Stefan Roese <sr@...x.de>, Leon Romanovsky <leon@...nel.org>,
        linux-rdma@...r.kernel.org, Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        Jim Wilson <wilson@...iptree.org>,
        Nicholas Piggin <npiggin@...il.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        David Abdurachmanov <david.abdurachmanov@...il.com>,
        linuxppc-dev@...ts.ozlabs.org,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        "David S. Miller" <davem@...emloft.net>,
        Lukas Wunner <lukas@...ner.de>, netdev@...r.kernel.org,
        Pali Rohár <pali@...nel.org>,
        Saeed Mahameed <saeedm@...dia.com>
Subject: Re: [PATCH v9 00/14] pci: Work around ASMedia ASM2824 PCIe link
 training failures

On Fri, Jun 16, 2023 at 01:27:52PM +0100, Maciej W. Rozycki wrote:
> On Thu, 15 Jun 2023, Bjorn Helgaas wrote:

>  As per my earlier remark:
> 
> > I think making a system halfway-fixed would make little sense, but with
> > the actual fix actually made last as you suggested I think this can be
> > split off, because it'll make no functional change by itself.
> 
> I am not perfectly happy with your rearrangement to fold the !PCI_QUIRKS 
> stub into the change carrying the actual workaround and then have the 
> reset path update with a follow-up change only, but I won't fight over it.  
> It's only one tree revision that will be in this halfway-fixed state and 
> I'll trust your judgement here.

Thanks for raising this.  Here's my thought process:

  12 PCI: Provide stub failed link recovery for device probing and hot plug
  13 PCI: Add failed link recovery for device reset events
  14 PCI: Work around PCIe link training failures

Patch 12 [1] adds calls to pcie_failed_link_retrain(), which does
nothing and returns false.  Functionally, it's a no-op, but the
structure is important later.

Patch 13 [2] claims to request failed link recovery after resets, but
actually doesn't do anything yet because pcie_failed_link_retrain() is
still a no-op, so this was a bit confusing.

Patch 14 [3] implements pcie_failed_link_retrain(), so the recovery
mentioned in 12 and 13 actually happens.  But this patch doesn't add
the call to pcie_failed_link_retrain(), so it's a little bit hard to
connect the dots.

I agree that as I rearranged it, the workaround doesn't apply in all
cases simultaneously.  Maybe not ideal, but maybe not terrible either.
Looking at it again, maybe it would have made more sense to move the
pcie_wait_for_link_delay() change to the last patch along with the
pci_dev_wait() change.  I dunno.

Bjorn

[1] 12 https://lore.kernel.org/r/alpine.DEB.2.21.2306111619570.64925@angie.orcam.me.uk
[2] 13 https://lore.kernel.org/r/alpine.DEB.2.21.2306111631050.64925@angie.orcam.me.uk
[3] 14 https://lore.kernel.org/r/alpine.DEB.2.21.2305310038540.59226@angie.orcam.me.uk