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Message-ID: <9741d204-1dd6-2cc2-c133-2ef49c8a404b@codeaurora.org>
Date: Tue, 19 Sep 2017 19:36:27 -0400
From: Sinan Kaya <okaya@...eaurora.org>
To: James Puthukattukaran <james.puthukattukaran@...cle.com>,
Bjorn Helgaas <bhelgaas@...gle.com>
Cc: "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v7] PCI: Workaround wrong flags completions for IDT switch
On 9/18/2017 4:05 PM, James Puthukattukaran wrote:
> Subject: [PATCH v7] PCI: Workaround wrong flags completions for IDT switch
> From: James Puthukattukaran <james.puthukattukaran@...cle.com>
>
> The IDT switch incorrectly flags an ACS source violation on a read config
> request to an end point device on the completion (IDT 89H32H8G3-YC,
> errata #36) even though the PCI Express spec states that completions are
> never affected by ACS source violation (PCI Spec 3.1, Section 6.12.1.1). Here's
> the specific copy of the errata text
>
> "Item #36 - Downstream port applies ACS Source Validation to Completions
> Section 6.12.1.1 of the PCI Express Base Specification 3.1 states
> that completions are never affected
> by ACS Source Validation. However, completions received by a
> downstream port of the PCIe switch from a device that has not yet
> captured a PCIe bus number are incorrectly dropped by ACS source
> validation by the switch downstream port.
>
> Workaround: Issue a CfgWr1 to the downstream device before issuing
> the first CfgRd1 to the device.
> This allows the downstream device to capture its bus number; ACS
> source validation no longer stops
> completions from being forwarded by the downstream port. It has been
> observed that Microsoft Windows implements this workaround already;
> however, some versions of Linux and other operating systems may not. "
>
> The suggested workaround by IDT is to issue a configuration write to the
> downstream device before issuing the first config read. This allows the
> downstream device to capture its bus number, thus avoiding the ACS
> violation on the completion. In order to make sure that the device is ready
> for config accesses, we do what is currently done in making config reads
> till it succeeds and then do the config write as specified by the errata.
> However, to avoid hitting the errata issue when doing config reads, we
> disable ACS SV around this process.
>
> The patch does the following -
>
> 1. Disable ACS source violation if enabled.
> 2. Wait for config space access to become available by reading vendor id
> 3. Do a config write to the end point (errata workaround)
> 4. Enable ACS source validation (if it was enabled to begin with)
>
> Signed-off-by: James Puthukattukaran <james.puthukattukaran@...cle.com>
> Signed-off-by: Yinghai Lu <yinghai@...nel.org>
>
> --
>
> -v2: move workaround to pci_bus_read_dev_vendor_id() from pci_bus_check_dev()
> and move enable_acs_sv to drivers/pci/pci.c -- by Yinghai
> -v3: add bus->self check for root bus and virtual bus for sriov vfs.
> -v4: only do workaround for IDT switches
> -v5: tweak pci_std_enable_acs_sv to deal with unimplemented SV
> -v6: Added errata verbiage verbatim and resolved patch format issues
> -v7: changed int to bool for found and idt_workaround declarations. Also
> added bugzilla https://bugzilla.kernel.org/show_bug.cgi?id=196979
>
>
> drivers/pci/pci.c | 40 ++++++++++++++++++++++++++++++++++++++++
> drivers/pci/pci.h | 1 +
> drivers/pci/probe.c | 42 ++++++++++++++++++++++++++++++++++++++++--
> 3 files changed, 81 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/pci/pci.c b/drivers/pci/pci.c
> index 6078dfc..4bca302 100644
> --- a/drivers/pci/pci.c
> +++ b/drivers/pci/pci.c
> @@ -2857,6 +2857,46 @@ static bool pci_acs_flags_enabled(struct pci_dev *pdev, u
> 16 acs_flags)
> }
>
> /**
> + * pci_std_enable_acs_sv - enable/disable ACS source validation if supported
> + * by the switch
> + * @dev - pcie switch/RP
> + * @enable - enable (1) or disable (0) source validation
> + *
> + * Returns : < 0 on failure (if SV capability is not implemented)
> + * previous acs_sv state (0 or 1)
> + */
> +int pci_std_enable_acs_sv(struct pci_dev *dev, bool enable)
> +{
> + int pos;
> + u16 cap;
> + u16 ctrl;
> + int retval;
> +
> + pos = pci_find_ext_capability(dev, PCI_EXT_CAP_ID_ACS);
> + if (!pos)
> + return -ENODEV;
> +
> + pci_read_config_word(dev, pos + PCI_ACS_CAP, &cap);
> +
> + if (!(cap & PCI_ACS_SV))
> + return -ENODEV;
> +
> + pci_read_config_word(dev, pos + PCI_ACS_CTRL, &ctrl);
> +
> + retval = !!(ctrl & cap & PCI_ACS_SV);
> + if (enable)
> + ctrl |= (cap & PCI_ACS_SV);
> + else
> + ctrl &= ~(cap & PCI_ACS_SV);
> +
> + pci_write_config_word(dev, pos + PCI_ACS_CTRL, ctrl);
> +
> + return retval;
> +}
> +
> +
> +
> +/**
> * pci_acs_enabled - test ACS against required flags for a given device
> * @pdev: device to test
> * @acs_flags: required PCI ACS flags
> diff --git a/drivers/pci/pci.h b/drivers/pci/pci.h
> index a6560c9..9d9a365 100644
> --- a/drivers/pci/pci.h
> +++ b/drivers/pci/pci.h
> @@ -339,6 +339,7 @@ static inline resource_size_t pci_resource_alignment(struct
> pci_dev *dev,
> }
>
> void pci_enable_acs(struct pci_dev *dev);
> +int pci_std_enable_acs_sv(struct pci_dev *dev, bool enable);
>
> #ifdef CONFIG_PCIE_PTM
> void pci_ptm_init(struct pci_dev *dev);
> diff --git a/drivers/pci/probe.c b/drivers/pci/probe.c
> index ff94b69..0aa6e02 100644
> --- a/drivers/pci/probe.c
> +++ b/drivers/pci/probe.c
> @@ -1945,8 +1945,8 @@ static bool pci_bus_wait_crs(struct pci_bus *bus, int devf
> n, u32 *l,
> return true;
> }
>
> -bool pci_bus_read_dev_vendor_id(struct pci_bus *bus, int devfn, u32 *l,
> - int timeout)
> +static bool __pci_bus_read_dev_vendor_id(struct pci_bus *bus, int devfn,
> + u32 *l, int timeout)
> {
> if (pci_bus_read_config_dword(bus, devfn, PCI_VENDOR_ID, l))
> return false;
> @@ -1961,6 +1961,44 @@ bool pci_bus_read_dev_vendor_id(struct pci_bus *bus, int
> devfn, u32 *l,
>
> return true;
> }
> +
> +
> +bool pci_bus_read_dev_vendor_id(struct pci_bus *bus, int devfn, u32 *l,
> + int crs_timeout)
> +{
> + bool found;
> + int enable = -1;
> + bool idt_workaround = (bus->self && (bus->self->vendor == PCI_VENDOR_ID_
> IDT));
> + /*
> + * Some IDT switches flag an ACS violation for config reads
> + * even though the PCI spec allows for it (PCIe 3.1, 6.1.12.1)
> + * It flags it because the bus number is not properly set in the
> + * completion. The workaround is to do a dummy write to properly
> + * latch number once the device is ready for config operations
> + */
> +
> + if (idt_workaround)
> + enable = pci_std_enable_acs_sv(bus->self, false);
> +
I think you want to do the part above as part of a quirk that runs before
the probe.
> + found = __pci_bus_read_dev_vendor_id(bus, devfn, l, crs_timeout);
> +
> + /*
> + * The fact that we can read the vendor id indicates that the device
> + * is ready for config operations. Do the write as part of the errata
> + * workaround.
> + */
Can you also run the code below as part of another quirk that runs after
enumeration?
You can very well enable ACS after that as well there.
> + if (idt_workaround) {
> + if (found)
> + pci_bus_write_config_word(bus, devfn, PCI_VENDOR_ID, 0);
> + if (enable > 0)
> + pci_std_enable_acs_sv(bus->self, enable);
> + }
> +
> + return found;
> +}
> +
> +
> +
> EXPORT_SYMBOL(pci_bus_read_dev_vendor_id);
>
> /*
>
>
--
Sinan Kaya
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm Technologies, Inc.
Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux Foundation Collaborative Project.
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