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From: "Kuppuswamy, Sathyanarayanan"  <sathyanarayanan.kuppuswamy@linux.intel.com>
To: Bjorn Helgaas <helgaas@kernel.org>
Cc: linux-pci@vger.kernel.org, linux-kernel@vger.kernel.org,
	ashok.raj@intel.com
Subject: Re: [PATCH v18 03/11] PCI/DPC: Fix DPC recovery issue in non hotplug case
Date: Tue, 24 Mar 2020 18:17:44 -0700
Message-ID: <e5af8e6e-ce37-eba4-330e-94b43bd0adb7@linux.intel.com> (raw)
In-Reply-To: <20200324234944.GA73526@google.com>

Hi Bjorn,

On 3/24/20 4:49 PM, Bjorn Helgaas wrote:
> I don't understand why hotplug is relevant here.  This path
> (dpc_reset_link()) is only used for downstream ports that support DPC.
> DPC has already disabled the link, which resets everything below the
> port, regardless of whether the port supports hotplug.
> 
> I do see that PCI_ERS_RESULT_NEED_RESET seems to promise a lot more
> than it actually*does*.  The doc (pci-error-recovery.rst) says
> .error_detected() can return PCI_ERS_RESULT_NEED_RESET to*request*  a
> slot reset.  But if that happens, pcie_do_recovery() doesn't do a
> reset at all.  It calls the driver's .slot_reset() method, which tells
> the driver "we've reset your device; please re-initialize the
> hardware."
> 
> I guess this abuses PCI_ERS_RESULT_NEED_RESET by taking advantage of
> that implementation deficiency in pcie_do_recovery(): we know the
> downstream devices have already been reset via DPC, and returning
> PCI_ERS_RESULT_NEED_RESET means we'll call .slot_reset() to tell the
> driver about that reset.
> 
> I can see how this achieves the desired result, but if/when we fix
> pcie_do_recovery() to actually*do*  the reset promised by
> PCI_ERS_RESULT_NEED_RESET, we will be doing*two*  resets: the first
> via DPC and a second via whatever slot reset mechanism
> pcie_do_recovery() would use.
When we fix this issue, if we make sure the reset logic is
implemented before we call .reset_link callback we should be
able to avoid resetting the device twice. Before we call DPC
.reset_link callback, the device link will not up and hence we
should not able to reset it.
> 
> So I guess the real issue (as you allude to in the commit log) is that
> we rely on hotplug to unbind/rebind the driver, and without hotplug we
> need to at least tell the driver the device was reset.
Agree
> 
> I'll try to expand the comment here so it reminds me what's going on
> when we have to look at this again:)   Let me know if I'm on the right
> track.
Yes, your understanding is correct.

  reply index

Thread overview: 27+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2020-03-24  0:25 [PATCH v18 00/11] Add Error Disconnect Recover (EDR) support sathyanarayanan.kuppuswamy
2020-03-24  0:25 ` [PATCH v18 01/11] PCI/ERR: Update error status after reset_link() sathyanarayanan.kuppuswamy
2020-03-24  0:25 ` [PATCH v18 02/11] PCI: move {pciehp,shpchp}_is_native() definitions to pci.c sathyanarayanan.kuppuswamy
2020-03-24  0:26 ` [PATCH v18 03/11] PCI/DPC: Fix DPC recovery issue in non hotplug case sathyanarayanan.kuppuswamy
2020-03-24 23:49   ` Bjorn Helgaas
2020-03-25  1:17     ` Kuppuswamy, Sathyanarayanan [this message]
2020-03-28 17:10       ` Bjorn Helgaas
2020-03-28 22:04         ` Kuppuswamy, Sathyanarayanan
2020-03-28 22:21           ` Bjorn Helgaas
2020-03-28 22:40             ` Kuppuswamy, Sathyanarayanan
2020-03-24  0:26 ` [PATCH v18 04/11] PCI/DPC: Move DPC data into struct pci_dev sathyanarayanan.kuppuswamy
2020-03-24  0:26 ` [PATCH v18 05/11] PCI/ERR: Remove service dependency in pcie_do_recovery() sathyanarayanan.kuppuswamy
2020-03-28 21:12   ` Kuppuswamy, Sathyanarayanan
2020-03-28 21:32     ` Bjorn Helgaas
2020-03-28 21:55       ` Kuppuswamy, Sathyanarayanan
2020-03-28 22:16         ` Bjorn Helgaas
2020-03-24  0:26 ` [PATCH v18 06/11] PCI/ERR: Return status of pcie_do_recovery() sathyanarayanan.kuppuswamy
2020-03-24  0:26 ` [PATCH v18 07/11] PCI/DPC: Cache DPC capabilities in pci_init_capabilities() sathyanarayanan.kuppuswamy
2020-03-24  0:26 ` [PATCH v18 08/11] PCI/AER: Add pci_aer_raw_clear_status() to unconditionally clear Error Status sathyanarayanan.kuppuswamy
2020-03-24  0:26 ` [PATCH v18 09/11] PCI/DPC: Expose dpc_process_error(), dpc_reset_link() for use by EDR sathyanarayanan.kuppuswamy
2020-03-24  0:26 ` [PATCH v18 10/11] PCI/DPC: Add Error Disconnect Recover (EDR) support sathyanarayanan.kuppuswamy
2020-03-24 21:37   ` Bjorn Helgaas
2020-03-25  1:00     ` Kuppuswamy, Sathyanarayanan
2020-03-26 22:36       ` Bjorn Helgaas
2020-03-24  0:26 ` [PATCH v18 11/11] PCI/AER: Rationalize error status register clearing sathyanarayanan.kuppuswamy
2020-03-31 15:28 ` [PATCH v18 00/11] Add Error Disconnect Recover (EDR) support Bjorn Helgaas
2020-03-31 16:28   ` Kuppuswamy, Sathyanarayanan

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