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Message-ID: <CAL-B5D0Y30-YYSgAOF_mpaiXp0mv63jQB_311AB4r55m01+vLA@mail.gmail.com>
Date: Tue, 22 Nov 2016 09:01:40 -0700
From: Myron Stowe <myron.stowe@...il.com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Johannes Thumshirn <jthumshirn@...e.de>,
Bjorn Helgaas <bhelgaas@...gle.com>,
linux-pci <linux-pci@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Alexander Graf <agraf@...e.de>, Hannes Reinecke <hare@...e.de>
Subject: Re: [PATCH 2/2] pci: Don't set RCB bit in LNKCTL if the upstream
bridge hasn't
On Mon, Nov 21, 2016 at 9:53 AM, Bjorn Helgaas <helgaas@...nel.org> wrote:
> On Wed, Nov 16, 2016 at 12:11:58PM -0600, Bjorn Helgaas wrote:
>> Hi Johannes,
>>
>> On Wed, Nov 02, 2016 at 04:35:52PM -0600, Johannes Thumshirn wrote:
>> > The Read Completion Boundary (RCB) bit must only be set on a device or
>> > endpoint if it is set on the root complex.
>>
>> I propose the following slightly modified patch. The interesting
>> difference is that your patch only touches the _HPX "OR" mask, so it
>> refrains from *setting* RCB in some cases, but it never actually
>> *clears* it. The only time we clear RCB is when the _HPX "AND" mask
>> has RCB == 0.
>>
>> My intent below is that we completely ignore the _HPX RCB bits, and we
>> set an Endpoint's RCB if and only if the Root Port's RCB is set.
>>
>> I made an ugly ASCII table to think about the cases:
>>
>> Root EP _HPX _HPX Final Endpoint RCB state
>> Port (init) AND OR (curr) (yours) (mine)
>> 0) 0 0 0 0 0 0 0
>> 1) 0 0 0 1 1 0 0
>> 2) 0 0 1 0 0 0 0
>> 3) 0 0 1 1 1 0 0
>> 4) 0 1 0 0 0 0 0
>> 5) 0 1 0 1 1 0 0
>> 6) 0 1 1 0 1 1 0
>> 7) 0 1 1 1 1 1 0
>> 8) 1 0 0 0 0 0 1
>> 9) 1 0 0 1 1 1 1
>> A) 1 0 1 0 0 0 1
>> B) 1 0 1 1 1 1 1
>> C) 1 1 0 0 0 0 1
>> D) 1 1 0 1 1 1 1
>> E) 1 1 1 0 1 1 1
>> F) 1 1 1 1 1 1 1
>>
>> Cases 0-7 should all result in the Endpoint RCB being zero because the
>> Root Port RCB is zero. Case 1 is the bug you're fixing. Cases 3 & 5
>> are similar hypothetical bugs your patch also fixes.
>>
>> Cases 6 & 7, where firmware left the Endpoint RCB set and _HPX didn't
>> tell us to clear it, are hypothetical firmware bugs that your patch
>> wouldn't fix.
>>
>> In cases 8, A, and C, we currently leave the Endpoint RCB cleared,
>> either because firmware left it clear and _HPX didn't tell us to set
>> it (8 and A), or because firmware set it but _HPX told us to clear it
>> (C).
>>
>> One could argue that 8, A, and C should stay as they currently are, as
>> a way for _HPX to work around hardware bugs, e.g., a Root Port that
>> advertises a 128-byte RCB but doesn't actually support it. I didn't
>> bother with that and set the Endpoint's RCB to 128 in all cases when
>> the Root Port claims to support it.
>>
>> It'd be great if you could test this and comment.
>>
>> If you get a chance, collect the /proc/iomem contents, too. That's
>> not for this bug; it's because I'm curious about the
>>
>> ERST: Can not request [mem 0xb928b000-0xb928cbff] for ERST
>>
>> problem in your dmesg log.
>
> Oops, I goofed and forgot to clear RCB by default.
> Here's the fixed one.
>
Testing on our end was successful again with this fix ;)
Tested-by: Frank Danapfel <fdanapfe@...hat.com>
Acked-by: Myron Stowe <myron.stowe@...hat.com>
>
> commit b7bff74c2e6babf12906291ee177f16444de81ad
> Author: Johannes Thumshirn <jthumshirn@...e.de>
> Date: Wed Nov 16 15:47:53 2016 -0600
>
> PCI: Set Read Completion Boundary to 128 iff Root Port supports it
>
> Per PCIe spec r3.0, sec 2.3.1.1, the Read Completion Boundary (RCB)
> determines the naturally aligned address boundaries on which a Read Request
> may be serviced with multiple Completions:
>
> - For a Root Complex, RCB is 64 bytes or 128 bytes
> This value is reported in the Link Control Register
>
> 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.
>
> - For all other system elements, RCB is 128 bytes
>
> Per sec 7.8.7, if a Root Port only supports a 64-byte RCB, the RCB of all
> downstream devices must be clear, indicating an RCB of 64 bytes. If the
> Root Port supports a 128-byte RCB, we may optionally set the RCB of
> downstream devices so they know they can generate larger Completions.
>
> Some BIOSes supply an _HPX that tells us to set RCB, even though the Root
> Port doesn't have RCB set, which may lead to Malformed TLP errors if the
> Endpoint generates completions larger than the Root Port can handle.
>
> The IBM x3850 X6 with BIOS version -[A8E120CUS-1.30]- 08/22/2016 supplies
> such an _HPX and a Mellanox MT27500 ConnectX-3 device fails to initialize:
>
> mlx4_core 0000:41:00.0: command 0xfff timed out (go bit not cleared)
> mlx4_core 0000:41:00.0: device is going to be reset
> mlx4_core 0000:41:00.0: Failed to obtain HW semaphore, aborting
> mlx4_core 0000:41:00.0: Fail to reset HCA
> ------------[ cut here ]------------
> kernel BUG at drivers/net/ethernet/mellanox/mlx4/catas.c:193!
>
> After 6cd33649fa83 ("PCI: Add pci_configure_device() during enumeration")
> and 7a1562d4f2d0 ("PCI: Apply _HPX Link Control settings to all devices
> with a link"), we apply _HPX settings to *all* devices, not just those
> hot-added after boot.
>
> Before 7a1562d4f2d0, we didn't touch the Mellanox RCB, and the device
> worked. After 7a1562d4f2d0, we set its RCB to 128, and it failed.
>
> Set the RCB to 128 iff the Root Port supports a 128-byte RCB. Otherwise,
> set RCB to 64 bytes. This effectively ignores what _HPX tells us about
> RCB.
>
> [bhelgaas: changelog, clear RCB if not set for Root Port]
> Fixes: 6cd33649fa83 ("PCI: Add pci_configure_device() during enumeration")
> Fixes: 7a1562d4f2d0 ("PCI: Apply _HPX Link Control settings to all devices with a link")
> Link: https://bugzilla.kernel.org/show_bug.cgi?id=187781
> Signed-off-by: Johannes Thumshirn <jthumshirn@...e.de>
> Signed-off-by: Bjorn Helgaas <bhelgaas@...gle.com>
> CC: stable@...r.kernel.org # v3.18+
>
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index ab00267..104c46d 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1439,6 +1439,21 @@ static void program_hpp_type1(struct pci_dev *dev, struct hpp_type1 *hpp)
> dev_warn(&dev->dev, "PCI-X settings not supported\n");
> }
>
> +static bool pcie_root_rcb_set(struct pci_dev *dev)
> +{
> + struct pci_dev *rp = pcie_find_root_port(dev);
> + u16 lnkctl;
> +
> + if (!rp)
> + return false;
> +
> + pcie_capability_read_word(rp, PCI_EXP_LNKCTL, &lnkctl);
> + if (lnkctl & PCI_EXP_LNKCTL_RCB)
> + return true;
> +
> + return false;
> +}
> +
> static void program_hpp_type2(struct pci_dev *dev, struct hpp_type2 *hpp)
> {
> int pos;
> @@ -1468,9 +1483,20 @@ static void program_hpp_type2(struct pci_dev *dev, struct hpp_type2 *hpp)
> ~hpp->pci_exp_devctl_and, hpp->pci_exp_devctl_or);
>
> /* Initialize Link Control Register */
> - if (pcie_cap_has_lnkctl(dev))
> + if (pcie_cap_has_lnkctl(dev)) {
> +
> + /*
> + * If the Root Port supports Read Completion Boundary of
> + * 128, set RCB to 128. Otherwise, clear it.
> + */
> + hpp->pci_exp_lnkctl_and |= PCI_EXP_LNKCTL_RCB;
> + hpp->pci_exp_lnkctl_or &= ~PCI_EXP_LNKCTL_RCB;
> + if (pcie_root_rcb_set(dev))
> + hpp->pci_exp_lnkctl_or |= PCI_EXP_LNKCTL_RCB;
> +
> pcie_capability_clear_and_set_word(dev, PCI_EXP_LNKCTL,
> ~hpp->pci_exp_lnkctl_and, hpp->pci_exp_lnkctl_or);
> + }
>
> /* Find Advanced Error Reporting Enhanced Capability */
> pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ERR);
> --
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